Q. When it started getting cold at night, I brought my two-year-old Meyer lemon tree inside and placed it about a foot away from a full spectrum floodlight, which is on for 12 hours a day. (The light burns the leaves if I put it any closer than a foot away!) It's potted in good, composted soil; I keep the soil moist; and use no chemicals on the tree. My neighbor has a similar tree (same age, same variety, purchased at the same time) that produced LOTS of lemons this summer, while mine produced none. It did produce lots of flowers last winter, but the little lemons all dropped off and the tree has hardly grown any since. I'm pretty disappointed and would love any advice you have to give!
- ---Christina; near Traverse City, Michigan
- ---Daniel in Montgomery County, PA
- ---Nancy in Texas
And I'm not exaggerating one bit. A Texas A & M map I found online reveals that the 'smokestack' at the top of the state is a chilly zone 6a (that means winter temps can get as low as minus 10 degrees F, which is 40 degrees below the freezing point of water and colder than my Pennsylvania garden ever gets), while the bottom of the tail is a downright tropical Zone 9b, where even a light frost is rare. So saying you're "in Texas" is about as helpful as "Hi! I live in North America!"
Anyway, most citrus should survive winter outdoors and unprotected down in the lower end of that Texas tail, as it does in places like Southern Florida, Arizona and California. But in most parts of the country, citrus is a potted plant that goes outdoors in the summer (afternoon shade for small plants; full sun for big ones) and indoors in the winter.
And whether it's a dwarf orange or that perfect-for-the-indoors Meyer lemon, all containerized citrus wants essentially the same thing: A naturally rich soil that drains well, a good amount of water, a surprising amount of food and warm temperatures.
I have no idea what "composted organic soil" might be, but the ideal medium for indoor citrus would be something like half compost and half soil-free mix. Specifically, the compost should be rich, black, screened, completely finished yard waste; and the soil-free mix should be a professionally blended potting mix containing ingredients like peat, perlite, and vermiculite; no actual 'soil' from the ground.
And yes, you need both parts of that equation. The soil must be naturally rich. And these plants absolutely require the excellent drainage provided by something like sand or a soil-free mix. Because, unlike most house plants, citrus does not like to dry out; so it needs its roots to be in a medium that can handle a lot of water. 'Always moist but never water-logged' is the ideal to strive for, and you need a light, loose soil component to try and achieve it.
Unlike most house plants, citrus is also a big eater; small, unproductive plants are probably hungry. The ideal food for the outdoor season would be a monthly shot of a liquid fish and seaweed fertilizer. But the fish component of these things is often a bit stinky, so use compost tea, worm castings, a bagged organic plant food designed for house plants or citrus, or a straight seaweed fertilizer during the indoor months. (Feed indoor plants sparsely over the winter if they don't get a lot of light; heavier if they get enough light to bear fruit.)
And keep it warm! Bring the plants back inside before night time temps drop into the 40s; don't take them out in the Spring until night time temps stay reliably in the 50s; and keep indoor temps up in the 60s—no chilly basements!
Under decent conditions, most indoor citrus will produce its wonderfully scented flowers, but the plants need BRIGHT light to induce fruit. The world's finest sunny South-facing window might provide the minimum amount (make sure it's well-insulated against night time cold!); but a solarium, heated greenhouse or well-insulated bay window is vastly superior.
Artificial light is also fine; just stay away from hot incandescent bulbs. Keep the tops of the plants about an inch away from a fixture containing four-foot-long 40-watt florescent tubes (two is good; four tubes is better), or try one of those new LED plant lights. Hanging any kind of bright light over a plant that's also in a bright well-insulated window should almost guarantee fruit.
And finally, although these kinds of plants can be grown from seed, virtually all store bought and/or nursery raised citrus is grafted onto a root stock. Only time will tell if that seed-started plant in Texas produces good fruit, bad fruit, or no fruit at all.