References + Links

An ongoing and informal list of the links in each post, this will be updated as needed.

Tips to grow a lemon tree in a pot?, r/gardening: https://www.reddit.com/r/gardening/comments/17g9r4i/soooo_tips_to_grow_a_lemon_tree_in_a_pot/

Reddit Citrus page, r/citrus: https://www.reddit.com/r/Citrus/

Citrus Varieties to Try at Home, Robin Sweetser, May 30, 2024, Almanac: https://www.almanac.com/growing-citrus-containers

How To Grow Citrus Trees Indoors, By Arricca Elin SanSone, Updated on September 29, 2022 (Fact checked by Jillian Dara), Southern Living Magazine: https://www.southernliving.com/garden/how-to-grow-citrus-trees-indoors

How to Grow and Care for Citrus Trees Indoors: Add fresh lemons, limes, and oranges you grow at home to your fruit bowl with these expert guidelines, By Blythe Copeland, Published on July 26, 2023, Martha Stewart: https://www.marthastewart.com/how-to-grow-citrus-trees-indoors-7565868

USDA Plant Hardiness Zones Map: https://planthardiness.ars.usda.gov/

NPR, The USDA’s gardening zones shifted. This map shows you what’s changed in vivid detail, By Daniel Wood, Connie Hanzhang Jin, Brent Jones and Jeff Brady: https://apps.npr.org/plant-hardiness-garden-map/

4 CITRUS TREES Northern Gardeners Can Actually Grow!, The Millenial Gardener, YouTube: https://www.youtube.com/live/MpF9lWJKCuA

National Gardening Association Forum, Potted Citrus Tree INDOORS - How far should I hang my grow light?: https://garden.org/thread/view/143078/Potted-Citrus-Tree-INDOORS---How-far-should-I-hang-my-grow-light/

University of Minnesota Extension, Growing citrus indoors, Author: Deborah L. Brown (Reviewed in 2024): https://extension.umn.edu/houseplants/growing-citrus-indoors

Effect of Aluminium on Root Growth, Cell-division Rate and Mineral Element Contents in Roots of Vigna unguiculata Genotypes, W.J. Horst, A. Wagner, H. Marschner, Institut für Pflanzenernährung, Universität Hohenheim: https://www.sciencedirect.com/science/article/abs/pii/S0044328X83801998

What is the Difference Between Deep Watering and Overwatering?, Four Winds Growers, September 2023: https://www.fourwindsgrowers.com/a/blog/what-is-the-difference-between-deep-watering-and-overwatering

Four Winds Growers Citrus Tree Instagram: https://www.instagram.com/fourwindsgrowers/

California Department of Food and Agriculture, Transport of Privately-Owned House Plants Into California From Other States, Frequently Asked Questions: https://www.cdfa.ca.gov/plant/pe/InteriorExclusion/houseplant_FAQ.html

LA Times, Can I bring plants into California? Yes, but know the rules, By Catharine Hamm, Feb. 26, 2020: https://www.latimes.com/travel/story/2020-02-26/plants-allowed-into-california-regulations

California Department of Food and Agriculture, Bringing Plants Into California, Questions and Answers: https://www.cdfa.ca.gov/plant/factsheets/TransportingPlantsCA.pdf

Should I Repot My Calamondin And If So, How?, Citrus x microcarpa, By Kiersten Rankel, Jun 18, 2024: https://greg.app/how-to-repot-a-calamondin/

Insecticidal Soap vs. Neem Oil: Which Works Better?, Humboldt Secret Supply: https://humboldtssecretsupplies.com/blogs/articles/insecticidal-soap-vs-neem-oil-which-works-better

Insecticidal Soaps for Garden Pest Control, Factsheet | HGIC 2771 | Updated: Jul 30, 2021, Clemson University Extension: https://hgic.clemson.edu/factsheet/insecticidal-soaps-for-garden-pest-control/

Treatment for Spider Mites on Citrus, Discussion in 'Citrus' started by KevyWestside, Nov 8, 2019: https://forums.botanicalgarden.ubc.ca/threads/treatment-for-spider-mites-on-citrus.96747/

How to identify and treat spider mites, Written ByJen Greene, Posted: March 10, 2021, updated: 4/14/2024: https://trexplants.com/blog/how-to-identify-and-treat-spider-mites

Does Diatomaceous Earth Control Fungus Gnats?, Mosquito Company: https://themosquitocompany.co.uk/blogs/news/does-diatomaceous-earth-control-fungus-gnats

How to control pesky fungus gnats in my potted Calamondin, Lime, Lemon and Orange plants? Cheri Abraham, PhD, Entomologist & Operations Manager, US Citrus, LLC: https://uscitrusnursery.com/blogs/citrus-simplified/how-to-control-pesky-fungus-gnats-in-potted-calamondin-lime-lemon-and-orange-plants

Hobbiest Gardening: Growing Fruit Tree Plants from Seed, Many people mistakenly believe that fruit trees come true to name from seeds, but the seeds from a fruit actually produce a new variety that is a hybrid of two plants., Rob Crassweller, Ph.D., Former Professor of Horticulture, Pennsylvania State University, June 21, 2023: https://extension.psu.edu/hobbiest-gardening-growing-fruit-tree-plants-from-seed

From Root to Fruit: The Intricate Process of Growing Fruit Trees, Moana Nursery: https://www.moananursery.com/2023/04/07/from-root-to-fruit-the-intricate-process-of-growing-fruit-trees/

Nuceller Embrony, Wikipedia: https://en.wikipedia.org/wiki/Nucellar_embryony

Polyembrony, Wikipedia: https://en.wikipedia.org/wiki/Polyembryony

Citrus Polyembryony, Written By Angel Villegas-Monter, Elisa Del Carmen Matínez-Ochoa, María Andrade-Rodriguez and Itzel Villegas-Velázquez, Submitted: 21 April 2022 Reviewed: 21 June 2022 Published: 16 July 2022, From the Edited Volume: “Citrus Research - Horticultural and Human Health Aspects” Edited by Mateus Pereira Gonzatto and Júlia Scherer Santos: https://www.intechopen.com/chapters/82707

Please help me understand “true to seed”, r/gardening, Reddit: https://www.reddit.com/r/gardening/comments/qcxyfn/comment/hhiyswl/

HARDY CITRUS FOR THE SOUTHEAST, by Tom McClendon: http://citruspages.free.fr/Hardy%20Citrus.pdf

Redwood Barn Nursery, http://redwoodbarn.com/pdfindex.html

Redwood Barn Nursery, Which citrus fruits will come true to type from seed?: http://redwoodbarn.com/PDF/Whichcitrusfromseed.pdf

Citrus, Wikipedia: https://en.wikipedia.org/wiki/Citrus

We Finally Know Where Oranges and Lemons Come From, In addition to finding where citrus come from, researchers have pinpointed the genetic origins of the fruits’ tart taste, By Jack Tamisiea, October 11, 2023: https://www.scientificamerican.com/article/we-finally-know-where-oranges-and-lemons-come-from/

DNA story of when life first gave us lemons, 8 February 2018 Helen Briggs, BBC News: https://www.bbc.com/news/science-environment-42960445

Botanical classification of citrus fruits, Citrus Pages: http://citruspages.free.fr/classification.php#classification

“Apples & Most Fruit Are Not True to Seed” Paul C Hay, Extension Educator, University of Nebraska-Lincoln Extension: https://extension.unl.edu/statewide/gage/Apples%20&%20Most%20Fruit%20Are%20Not%20True%20to%20Seed.pdf

7 Citrus Tree Mistakes to Avoid, Epic Gardener, YouTube: https://www.youtube.com/watch?v=nd1ws1fwpqc&t=46s

Citrus Pruning | Cut, Pull & Bend Branches For MAX Fruit Yields! IV Gardening, YouTube: https://www.youtube.com/watch?v=jVbr5noPAQo&t=1111s

How to prune a lemon tree – expert tips to keep it in shape, By Melanie Griffiths, last updated 30 March 2023, Homes & Gardens Magazine: https://www.homesandgardens.com/advice/how-to-prune-a-lemon-tree

When and Where Should I Trim My Calamondin?, Citrus x microcarpa, By Kiersten Rankel, Jun 18, 2024: https://greg.app/how-to-prune-calamondin/

Indoor lemon tree. Should I prune or leave it as it is? r/Citrus, Reddit: https://www.reddit.com/r/Citrus/comments/y45nuf/indoor_lemon_tree_should_i_prune_or_leave_it_as/

Is it ok to cut off citrus tree thorns? Ask an expert, Published: Aug. 06, 2022, By Kym Pokorny | For The Oregonian/OregonLive: https://www.oregonlive.com/hg/2022/08/is-it-ok-to-cut-off-citrus-tree-thorns-ask-an-expert.html

Thorns On Citrus Trees: Why Does My Citrus Plant Have Thorns?, By Amy Grant, last updated 22 April 2021: https://www.gardeningknowhow.com/edible/fruits/citrus/thorns-on-citrus-trees.htm#

The Orchard People, The Simple Art of Grafting Fruit Trees: A Complete Guide: https://orchardpeople.com/grafting-fruit-trees/

What Is A Graft Collar And Where Is The Tree Graft Union Located, By Bonnie L. Grant, last updated 6 January 2023: https://www.gardeningknowhow.com/ornamental/trees/tgen/what-is-a-graft-collar.htm

University of Florida, Citrus Propagation, Publication #HS1309, Release Date: April 9, 2021: https://edis.ifas.ufl.edu/publication/HS1309

Natural Human History of Grafting and Budding, Cornell University: https://courses.cit.cornell.edu/hort494/mg/history/HistGB.html

How (&Why) To GRAFT FRUIT TREES | Figs, Apples, Citrus, Stone Fruit+, IV Gardening, YouTube: https://www.youtube.com/watch?v=98YjOBegVdU&t=1663s

Grafting Citrus Trees with the Patch Bud - Making a Fruit Cocktail Tree, Fruit Mentor, YouTube: https://www.youtube.com/watch?v=_w051zyackM

Grafting and Budding Nursery Crop Plants, Ted Bilderback, Director, JC Raulston Arboretum and Cooperative Extension Nursery Specialist Horticultural Science, R. E. Bir, T. G. Ranney, North Carolina State Extension, Publication date: June 30, 2014: https://content.ces.ncsu.edu/grafting-and-budding-nursery-crop-plants

What I’ve learned about fruit tree grafting 🌱🌳🍋🍊🍏🍎🥑🍑🍒🥭🍐🍇

Something I was surprised to learn was that none of the citrus fruit we buy at the supermarket is grown from seeds in the ground, they’re all grown from grafted trees. Even the lemon and orange trees growing seemingly “wild” in people’s yards in places like Los Angeles, San Diego, or Florida are very likely to be a grafted tree that got planted outdoors. 


Grafting involves cutting a scion from a proven fruit-bearing tree and attaching it to part of a separate rootstock it will grow off of, essentially as a clone. If you’re ever close enough to a citrus tree in a yard or in a grove, see if you can spot the graft collar close to the base of the trunk, it might be visible on a large enough tree.

Since most fruit trees don’t grow true to seed, there’s nothing wrong with the practice of grafting. This is not an especially modern method, grafting has been practiced for at least 4,000-2,000 years in various parts of the world.

As we are about to see for ourselves with this citrus adventure, it takes a long time and a lot of care to raise a fruit tree from seed, plus it takes years to start producing fruit, if it does at all. Based on what we’ve learned about the nature of citrus genetics, grafting is the only real way to grow fruit trees at any scale that are guaranteed to consistently produce desirable fruits. 

I also enjoyed various videos of professional arborists using all kinds of techniques to graft and grow different kinds of trees. 


Of course, you can let this tree grow as-is and let it live its natural lifecycle. Or, if you’re into this sort of thing, this tree could become a rootstock you can graft onto. Or, if it produces desirable fruit, then parts could be used as a scion.

I emphasize the distinction between grafted citrus trees and ones grown from seeds; the growing process is quite different, so keep this in mind when you’re troubleshooting and researching for your tree in the future as it grows.

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Calamansi shoots in the sun (August 2024)

Misc. notes on long term development, and all about pruning 🪚✂️🍃🐝🌱🪴🌳

So, if things go according to plan, in about a year you should have at least 1-foot of growth, and it might start to look like an actual tree.

Outdoors, these trees can grow to be 8-25 feet tall, when grown in containers indoors, these might reach 2-4 feet tall. 


Between now and Autumn 2025 it will look a bit scraggly here and there as it grows; especially when young, and some leaves may drop in partial dormancy. Expect there to be a noticeable and possibly long awkward phase. But, don’t lose hope: see this phase through and don’t give up on that tree! Yes, I’m telling myself this as much as I’m telling you! 


Pruning won’t be necessary or even advisable until well after two years, likely even longer. Pruning directs energy towards producing flowers and fruits by eliminating dead branches and unhealthy growth. Years from now, hopefully it’ll be growing strong enough where you’ll have to occasionally prune it to encourage growth.

As over-pruning can quickly kill a healthy tree, generally the consensus seems to err on the side of restraint with pruning. There are many, many resources available about pruning citrus trees. You should absolutely look these up, especially if you (like me) have never pruned anything before. Please feel free to get in touch to share your updates and progress! 

The best time to prune branches is very late winter or early spring, just ahead of new growth, so the best and most productive branches experience peak season. Late season pruning is not recommended as you might mistakenly cut off forthcoming growth. 

These trees will almost certainly produce thorns as they mature. These are natural defenses to protect the tree and fruit from predators. It’s likely to produce thorns regardless of whether it produces fruit. It’s most likely to develop thorns early in maturity, when the tree is most vulnerable, and it may or may not stop growing them as it ages. 

The good news is: it usually takes over year for thorns to develop, and properly pruning the thorns won’t damage or harm the tree. In fact, because they are sharp, this might be necessary if you have pets or young children. 


It will take at least 1-2 years or likely much longer, if it happens at all, but if your indoor specimen(s) produce flowers and you keep it indoors without access to pollinators like bees, it’s still possible to method-act as a bee by using a paintbrush or a q-tip to spread the pollen around to the flowers by hand. 


If you are successful in your pollination methods, the flower parts might eventually (hopefully) mature into fruit! And yes, it will probably grow some form of thorns the whole way. Ain’t that damn near poetic? 

A kumquat sprout in the sunlight, August 2024

The question of fruit, and a word on citrus tree genetics 🍋🧬🍊🔬🍋🧬🍊

“Life, uh, finds a way.” 

(Jurassic Park, dir. Stephen Spielberg, Universal Pictures, 1993) 


It’s not guaranteed these shoots will grow into trees that flower and produce fruit, you’ll just have to wait and see. However, even if they never flower or produce fruit, you will still have a lush, evergreen miniature shrub tree, probably with sweet-scented leaves. 


The reason citrus trees do not always bear desirable fruit is because of the mixed parental genetics within the seed itself. Citrus seeds are frequently nucellar polyembryonic seeds, meaning there’s more than one embryo per seed. 

In short, plants do this to create genetic variation to increase its chances of survival. Seeds with varying copies of its genetic material with different potential traits to express are more likely to survive and adapt than identical single copies. In fact, with a few exceptions, most fruit trees are not “true to seed,” or, will not produce fruit identical to the tree it came from. 

The calamansi almost always sprouted multiple shoots. The kumquats almost always sprouted single shoots. If you have a polyembryonic shoot, you might have to select the strongest shoots for long term growth at your discretion. Re-pot and grow them separately; as one will inevitably take energy from the other. 

With polyembryonic seeds like most of the calamansi, it’s likely that shoots of multiple parentage within one seed have sprouted, and one of these will grow true to seed. The monoembryonic seeds that only grew one shoot, like almost all of the kumquats, are not likely to grow true to seed and won’t produce fruit like the parent tree. 

The seeds I planted contain genetic material from multiple generations of everything those fruits were a hybrid of. This is not unlike how we humans are the product of two parents but don’t have identical traits or genes of solely one or the other. As offspring, we may resemble one another and both parents, but we’re not always exactly alike, and certain traits are not always guaranteed to be expressed. 

In the case of fruit trees, the resulting fruit you grow might be the same as, or better than, or (more likely) worse than the fruit the seed came from. The odds are high that it will be different somehow.

🍋🧬🍊🔬🍋🧬🍊

All citrus fruits are hybrids of two or more original species: the citron, the pomelo, and the mandarin orange. These ancestral species originated in various tropical and sub-tropical regions of the Asian continent (India, Southeast Asia, and China). The drastic periods of climate change during the Miocene and Pliocene epochs (between 23M and 5M years ago) enabled these ancestor species to grow wild, with specimens and pollen samples dating back to these periods; eventually leading to human cultivation starting around 6,000-3,000 years ago.

Today, we know the descendants of these ancestral fruits as oranges (mandarin + pomelo), lemons (bitter orange + citron), grapefruits (sweet orange + pomelo), tangerines (mandarin orange varieties + pomelo), Meyer lemons (mandarin + citron + pomelo), Clementines (sweet orange + mandarin), and more.

Kumquats are classified as citrus japonica, and contain different cultivars (Meiwa, Nagami, etc.). The seeds I germinated and planted almost always grew one shoot, or, are monoembryonic. 

Calamansi are a hybrid of mandarin orange + kumquat. I noticed that the Calamansi seeds were almost always polyembryonic, and grew multiple shoots, all of which show slightly variable traits and leaf shapes. I didn’t label Group 1 so my labels are educated guesses, based on leaf shape. 

Obnoxious Beasts (And How To Kill Them) 🦟🐜🐞🪰🔫

An ongoing list of common citrus tree pests and how to eliminate them. As this is my first time growing citrus trees, I have no first hand experience dealing with these (except for fungus gnats), so I’m keeping this here for the inevitable need and will be updating as I go.

Fungus gnats: harmless swarms will come and go and they aren’t necessarily a sign of anything bad, they’re inevitable when there’s excessive moisture in the soil. While they’re not strong fliers and don’t bite, they’re still a nuisance. You can control or eliminate them by using both sticky traps and diatomaceous earth together, along with letting soil dry out completely between waterings. I strongly suggest eliminating them when possible. Although, I have never found hydrogen peroxide solution to be effective, only a combination of sticky traps to catch adults and a significant amount of diatomaceous earth to kill the larvae. 


Spider mites: these are more likely to be a problem on more mature plants, and harder to get rid of than gnats. They are extremely small, smaller than a pinhead, so you’ll have to look at the leaves very closely to see them. These are best treated by gently cleaning off leaves with insecticidal soap, as well as spraying Neem oil on the leaves and soil. Diluting the Neem oil with water will help prevent any leaf burning, along with washing off the leaves with a damp towel, especially for young shoots too delicate to be exposed to natural rainfall.

Thrips:

https://www2.ipm.ucanr.edu/agriculture/citrus/Citrus-Thrips/

https://www.thegreenpinky.com/best-insecticides-thrips/

Scale:

https://www.fruitsaladtrees.com/pages/citrus-scale

https://www.reddit.com/r/Citrus/comments/14y33o4/scale_treatment/

https://www.gardeningknowhow.com/edible/fruits/citrus/controlling-citrus-scale.htm

https://www.finegardening.com/article/controlling-scales-a-common-pest-of-fruit-trees

Citrus Leafminer:

https://extension.uga.edu/publications/detail.html?number=C1145&title=how-to-control-citrus-leafminers

https://www.yamagamis.com/blog/how-to-treat-citrus-leafminers

https://www.agric.wa.gov.au/pest-insects/citrus-pests?nopaging=1

https://www.engalls.com.au/advice/citrus-pests-and-diseases/

Re-potting, soil health, root development, and room to grow 🪴⏳📏🗓️📈

“No! Try, not. Do or do not; there is no try.” 

(Yoda, The Empire Strikes Back, dir. Irvin Kershner, 20th Century Fox, 1980)

Citrus trees are best put in a container where roots aren’t touching the ground. Having the potting container with drainage holes suspended inside a larger container, preferably terracotta or plastic, is ideal. 


Do not let the roots soak in standing water, do not let the container sit in standing water. When in doubt, monitor the roots and make them work a little harder to find water; especially since they are prone to rotting from overwatering. 


Monitor root growth and condition: if roots are growing far out past the current container and are looking dry, then they need somewhere to grow, so re-pot it in a bigger container soon to allow for expansion. When in doubt, leave it be, because re-potting will cause shock, and the younger a shoot is, the more vulnerable it is. 


In Zones 6-7, re-pot these specimens when emerging from seasonal dormancy: late winter/early spring. In Zones 5 and above, you may experience slower growth and your mileage may vary. But generally, it’s not recommended to re-pot when it’s resting dormant in the late autumn and winter, and peak season growth could be interrupted by re-potting too late in the summer or early autumn. 

Choose a container one size bigger, but avoid an overly large one. Think of it like buying shoes for growing children; prioritize for short term growth within reason, knowing that jumping straight into adult size shoes would be both impractical and counterproductive. 


In my first experiment with the lemon shoots (RIP), I used both tall and deep containers and a shallow and wide one. I noticed the shoots seemed to do better in the tall/deep style. 

🪴⏳📏🗓️📈

Only clean, fresh potting soil should be used. Never reuse soil from other plants, no moldy parts, no organic bits of matter that could rot. If you have access to good quality compost, use that, too, but only use compost that you trust. Well-cured, healthy compost will provide excellent nutrients and root support to the tree, but improperly cured compost will cause rot, odor, and attract pests. 


For indoor growing, I do not recommend adding in coffee grounds, used tea bags, or anything that might cause fungus. I think that caused a particularly bad infestation of fungus gnats in that first batch of shoots. By completely drying the soil to kill the gnats, I inadvertently dehydrated the shoots and weakened them, breaking in the breeze. With these shoots, I added enough soil acidifier when planting these so you should never need to add un-composted organic material.

Adding a small amount of sand aids drainage, although too much sand can prohibit root development. The sand I used in this mixture was taken home from Jacob Riis beach in an 8 oz. takeout container. Hand-gathered beach sand should be sanitized by spreading it on a rimmed baking sheet in a 400 degree oven for 20-25 minutes, and thoroughly cooled before mixing into the soil. Anakin Skywalker, who hates sand for Tatooine related reasons, could never (it gets everywhere).


Cleanliness is important because citrus trees are especially vulnerable to diseases and fungal infections** that are very difficult (and costly) to control. If you use soil or tools that were exposed to diseased plants, or if you use containers that haven’t been thoroughly cleaned, the tree will have issues from the start. 



** Because citrus trees are so vulnerable to disease and pests, and because almost all the citrus trees growing in California are grafted clones with little natural built in protection against hitherto unknown diseases, the state of California highly regulates all citrus plants, fruits, and leaves entering the state via flight and freight. One can easily drive into the state with plants in a personal vehicle, nobody checks that anywhere, but you are running the risk of introducing pests and diseases to native trees. So, if you care about the health of tree species on a larger scale: Please do not transport these trees into the state of California, it’s technically illegal.

This is about water requirements 💦💧🌧️🚿🚰🌱🪴🌿🍊🍋

“…next to you, we ALL have a drinking problem!” 

(Burn After Reading, dir. The Cohen Brothers, Focus Features, 2008) 

Citrus trees are heavy drinkers, but they’re a bit particular: they don’t tolerate sitting in dampness, and they can’t drink too much or too little. They prefer infrequent, deep waters over regular, surface waters. They like a good binge and then dry out thoroughly between sessions. When in doubt, let the soil dry out. 

Expect to water the shoot every 7-10 days, or more frequently in hot conditions. Citrus trees will go partially dormant in cold enough temperatures and during significant seasonal fluctuations; reduce the watering schedule accordingly. When dormant and during the winter season, you will water considerably less, maybe once or twice a month (your mileage may vary). 

But don’t let it stay completely dry for too long, either, the roots will eventually dehydrate. An indication to water is if the top layer of soil is visibly dry, check by testing soil dampness by hand, or with a bamboo skewer. 

If it’s showing signs of wilt or heat stress in hot, direct sun without enough water, give it a good watering and move it to indirect sunlight for a day or more. Leaf-curl or blackening leaves can indicate over-watering and/or lack of sunlight; monitor and correct accordingly. 

Citrus roots are especially prone to root rot, so you must cut whatever soil mix to be well-draining. Use a combination of perlite, orchid mix, peat, sand, etc. Mix it thoroughly without letting the soil get too compacted, keep it fluffy when possible. Using overly compacted soil that doesn’t drain well will kill it very quickly. 

I wouldn’t worry about using a special filter for the water. Unless your tap water is especially undrinkable, it seems like most people use whatever they drink at home. Mineral buildup from hard water would only be an issue in very extreme conditions. If you collect rainwater, use that! But overall, it seems like there’s no need to complicate what type of water to use.


💦💧🌧️🚿🚰

Not only can they be thirsty girlies, citrus trees are also heavy feeders, and will require occasional fertilizer and a nutrient rich soil. They thrive in very acidic soil or medium, and you must add a soil acidifier component. With my shoots, I already added acidifier, and can provide you with extra (let me know).

If you want, I can provide you with enough extra Espoma for two re-pottings, maybe three. Generally, for every 1 lb (16 oz.) of soil, I mixed in a generous 8 oz. of acidifier, which is actually quite a lot. But, I did this knowing citrus trees need very acidic soil, knowing I can taper off including it over time. I do not have a soil ph tester, but if you have one, this is a great excuse to use it in order to check pH levels and maintain a consistent formula. 

If you’re not familiar with this brand of acidifier, the way Espoma works is the sulfur chips are dissolved by organisms in the soil which convert it to sulphuric acid. The gypsum counteracts the development of toxic soluble aluminum that results from acidifying the soil. The Espoma brand is a slow release formula that takes about 6 months to reach potency, so do NOT add any more to the current cup. You may need some the first or second time you re-pot the tree. Other types of acidifiers are available, your mileage may vary. 

Espoma Soil Acidifer

You’ll probably need a bit of fertilizer every season, and if you want I can provide you with some extra. The Osmocote plant fertilizer is high in nitrogen, potassium, and phosphate; it’s delivered via little resin balls which slowly release nutrients. It normally takes about 4 months before you need to replenish it, but in growth seasons you may need to add more. When in doubt, hold off and avoid over-fertilizing. 

Osmocote plant fertilizer

These measurements are not definitive, this is just what’s worked for me so far. Your mileage may vary and your research may lead you to other conclusions. Again, you’re welcome to share your progress in the comments!

Say more about light requirements and hardiness zones ☀️🌤️🌞🪴🌱

Citrus trees need 6-10 hours of sunlight for the entirety of their lifetimes. Direct light must be available; ideally with an option for bright indirect light in case you need to move it to a cooler spot. South facing windows with access to consistent daylight from east and west are ideal. 

In peak conditions during spring, summer, and early fall, assume 8-10 hours of direct sunlight. In the late fall and winter months, strive for 6-8 hours of direct sunlight. I plan to both move mine to an enclosed area and use an artificial grow light during the wintertime to make up for the change in direct sunlight and temperature. 

Citrus trees thrive between 60-90F. Mild to moderate humidity is ideal, and you can substitute with misting or use a humidifier in a dry climate (or, a nyc apartment microclimate). Within reason, the warmer the better as far as temperature goes. Choose the least-drafty, most consistently warm and sunny spot you have available. 

Important to note: be very mindful about keeping it in an excessively damp environment (like inside a shower), as citrus trees are so prone to root rot. Constant, excessive heat (especially for very young shoots) isn’t ideal either, as the shoots will experience heat stress and wither away at temps above 110F. 


Citrus trees thrive between US Zones 9, 10, and 11. In the US, these are the only Zones where they can be planted and grown outdoors year round. Below are USDA hardiness zone resources, but the NY tristate area is in Zone 7. Here, growing citrus trees will be a largely indoor endeavor.

Here’s a cheat sheet of the USDA growing zones in the northeast: 

  • The NYC area and the tristate area (including NJ and the Philadelphia, PA region) is in Zone 7b. 

  • Just north, the area from Hudson Valley up towards Albany, as well as the neighboring region of southwestern New England (western Connecticut and Massachusetts), is in Zone 6a. 

  • Farther north, towards upstate NY (i.e. the longitude between Saratoga to Syracuse and Rochester) is designated as Zone 5b.

  • Eastern Massachusetts in the Boston metro area and back bay, Suffolk County, Plymouth County, and Cape Cod are between Zones 7a to 7b. 

Look up your growing zone on the USDA website: https://planthardiness.ars.usda.gov/ 

This article from NPR also has useful information about the recent updates to the zone map: https://apps.npr.org/plant-hardiness-garden-map/ 

Calamansis and kumquats are both somewhat more cold tolerant than other citrus varieties, especially when grown indoors. However, being what they are, during winter months in Zones 5-7, these trees must be kept indoors and away from any direct drafts during the winter. 

In short, do not plant this tree outdoors in Zones 5-7 and expect it to survive. The winters here are too cold, too dark, and last too long. There are ways to attempt this in cooler zones (e.g. Zone 8), but it takes a lot of work, expertise, and investment to protect the trees from frost.  

Do not let the young shoots sit outside in any conditions, for any reason. Even light breezes will blow over and break immature shoots, which I learned the hard way with my very first lemon tree shoots (RIP). When they’re very young and delicate, I don’t even recommend keeping them near an open window; the breeze might be too strong. 

My very first group of lemon shoots, which I started in late March, died a sudden, painful death in late May. One day, I put them outside on my fire escape for a few hours for the daylight, and the summer breeze broke the delicate shoots and killed them all. 

So, as tempting as it is to let them photosynthesize outdoors, keep young specimens indoors away from the elements for as long as possible. Later in its maturity, you might be able to move the container outdoors part-time (e.g. to a sunny porch on nice days in the summer), and you can stake it so it’s more secure in the elements. But only do this for mature trees that are strong enough, at least 1 year or older. 

Between July 2 and August 4, I planted the germinated seeds in basic 3.5 oz. plastic cups that I hand-cut drainage holes into, and sprouted them in makeshift mini greenhouses with plastic dollar store bins. By late winter/early spring 2025, it will be time to transplant to a slightly larger cup. 

You will have far fewer to care for than I did, but here are photos of my setup for Group 1 shoots in my bathroom (there are about 56x).

All about these shoots

“Come play with us…”

(The Shining, dir. Stanley Kubrick, Warner Bros., 1980)

Calamansi, Kumquat, and Lemon Seedlings Overview:

The first date is when I started germinating them, the second date is when I planted the sprouts. 

  • Group 1: Germinated (start): 6/26/24, Planted (seedlings): 7/2/24 (calamansi, kumquat, and 1x lemon)

  • Group 2: Germinated (start): 7/2/24 and 7/7/24, Planted (seedlings): 7/16/24 (calamansi and kumquat)

  • Group 3: Germinated (start): 7/17/24, Planted (seedlings): 8/4/24 (all lemon)

  • Group 4: Germinated (start): 8/12/24, Planted (seedlings): 8/25/24 (all lemon)


The origin of these seeds are as follows: 

  • Calamansi: seeds were saved from fruits that were available through work. 

  • Kumquat: purchased packaged kumquat fruits from two sources, the supermarket in northwest Connecticut, and from packaged fruits from a street seller in NYC Chinatown. 

  • Lemons: most info points to the lemons probably being either Eureka or Lisbon lemons, which are most commonly found in supermarkets (where I found these) but I am not certain. 

  • I’m not sure exactly what variety of kumquats and calamansis these are, I don’t know who the father is. 

I unintentionally acquired these seeds during mid to late June, and Group 1 was germinated and started in late June. I peeled off the outermost, beige colored, protective hull of each seed and germinated the hulled seeds in damp paper towels in a plastic bag. 

What would have been better is to have started the seeds in the springtime, so the shoots experience this year’s full growth season. This was a hot and sunny summer in NYC, and I happen to have abundant south-facing daylight for a full 8-10 hours most days in the summer; so despite a late start, they are still growing. 

So, keep in mind as you monitor growth, and plan for transplanting, that these shoots are about a quarter to a half season behind.

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Between July 2 and August 4, I planted the germinated seeds in basic 3.5 oz. plastic cups that I hand-cut drainage holes into, and sprouted them in makeshift mini greenhouses of plastic dollar store bins. On August 25, I transplanted those seedlings to larger 7 oz. cups. Sometime around late February to March, it will likely be outgrowing this cup and will need to be transplanted to the next size up to accommodate peak growth throughout April-July. By next July, the specimen will be 1 year old. 

Most of the advice and information I’ve found is that citrus trees require varying levels of care year round. Even in partial dormancy, they still require a minimum of 6 hours of daylight, occasional water, and monitoring and treating any pests (which they are prone to, even when grown indoors).

Citrus trees largely seem like the opposite of a passive-care plant like a snake plant or a ZZ plant; you can’t completely ignore them for full seasons at a time. Especially in Zones 6-7, and especially as immature specimens, they require active attention year round.

Each seedling is planted with the following mixture: 

  • Miracle Grow Cactus, Palm & Citrus Potting Mix (fast draining formula) 

  • Espoma Organic Soil Acidifier 

  • Beach sand 

  • Osmocote flower & vegetable plant fertilizer 

  • Diatomaceous earth (fungus gnat prevention) 

Project Pomona: Introduction 🍊⚜️🍊

Welcome!

If you are reading this, then you are someone I know who is interested in learning more about the kumquat, calamansi, and lemon tree shoots I’ve been growing from seed.

Maybe you identify as an intermediate (or above) plant person, and are interested in acquiring a couple of these citrus tree seedlings for yourself (I would love to give you some, please inquire!). 

CONTENT LINKS:

  1. All About These Shoots

  2. Say more about light requirements and hardiness zones ☀️🌤️🪴🌱

  3. This is about water requirements 💦💧🌧️🚿🚰

  4. Re-potting, soil health, root development, and room to grow 🪴⏳📏🗓️📈

  5. Pests 🦟🐜🪰🔫

  6. The question of fruit, and a word on citrus tree genetics 🍊🍋🧬🔬🧬 

  7. Misc. notes on long term development, also get excited about pruning 🪚✂️🍃🐝🌱🪴🌳

  8. What I’ve learned about fruit tree grafting 🌱🌳🍋🍊🍎🥑🍑🍒🥭🍐

  9. References + Links

To be clear: this is my first time growing any kind of tree indoors, I’ve been learning as I go. I’m sharing what I’ve learned so far as a series of ongoing notes for myself, and if it helps anyone else searching for the exact same information I did.

Citrus tree care is not always intuitive for first time growers like me, I’ve discovered there is a learning curve. Since this spring, I’ve done a lot of online research on how to grow citrus trees indoors. And it’s fascinating! 

For anyone interested in staying connected on our shared citrus adventure, I have turned comments on so you can share updates on your progress, anything that I haven’t covered that is working, and any new information they’ve learned.

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  • A minor Roman deity, with no Hellenic equivalent, Pomona is a wood nymph who watches over and protects fruit bearing trees and cares for their cultivation. Her sacred attribute is a pruning knife. The Roman poet Ovid described her pure, radiant beauty and her passion for gardening in Book 14 of his narrative poem, Metamorphoses. 

    Her name originates from “pomum,” the Latin word for orchard fruit, the French word for apple (“pomme”) is subsequently derived from this; and she is often associated with apples and apple trees. Only two types of citrus fruits were known to Ancient Romans, the citron and the lemon, and they would have been either status symbols to the elite, or used in ceremonial or medicinal purposes. Cultivated fruits such as apples, pears, quinces, plums, figs, and pomegranates were more commonly consumed.

    Although Pomona is also frequently depicted in a orchard or garden, often with a cornucopia of fruits, she is not associated with the act of harvesting, but with the flourishing, abundance, and divinity of the trees themselves. 

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