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).
