You don't have to live in the tropics to grow subtropical fruits such as lemons, oranges, grapefruits, passion fruits, and figs. By growing fruits in containers, you have the opportunity to move plants to a sheltered spot for the winter -- and work around problems such as poor soil.
There's a different set of guidelines to growing fruits indoors, such as in a greenhouse, cool basement, or sunny windowsill. Many of these plants need pampering and more effort than the average houseplant. Follow these tips and you'll be on your way to having fresh fruit grown in your home.
Before selecting a container, consider your needs. Think about size, durability, and weight. Smaller plants can grow for a couple of years in a traditional 8-inch-wide container; larger varieties may need to be moved to increasingly larger containers until they're in 36- or 48-inch-wide pots. Keep in mind that the bigger the container, the harder it is to move.
There are many options for containers, and advantages and disadvantages to every choice. Terra-cotta, stone, and ceramic containers are durable but heavy. Wood containers are attractive and generally lightweight but can rot over time. Containers are also available in synthetic materials such as plastic, polystyrene, and other modern composites. These are lightweight, long-lasting, and fabricated to resemble many kinds of materials. Whichever container you choose, make sure it has drainage holes.
Containers allow you to provide the perfect soil -- a combination of optimal aeration and drainage with good moisture retention and the ability to hold nutrients. Garden soils won't cut it in a container. They rarely drain properly, are usually too heavy, and often contain disease organisms. But there are many potting mixes specifically formulated for growing plants in containers. Many of these contain no real soil at all. Consider using a mix that has moisture-control amendments and controlled-release fertilizer already mixed in to cut down on watering frequency and feeding.
You can also whip up your own potting mix. For 1 cubic yard, take equal parts peat moss or composted fir or pine bark and mix in perlite, dampening the mix as you go. If you wish, add in a slow-release fertilizer to the mix. Combine by scooping the ingredients into a cone-shape pile, letting each shovelful slide down the cone. To get a thoroughly mixed product, repeat the cone-building three to five times.
Subtropical fruits grown in containers require more frequent watering than those grown in the ground. Make sure to use enough water to soak the entire root ball. Pay careful attention when you water to the moisture that comes out of the pot. If it all seems to rush out of the drainage holes immediately, your plant has probably gone too long without water and the potting mix is shedding moisture instead of absorbing it. Add small amounts of water slowly to help the potting mix take in the moisture.
To compensate for nutrients lost from watering, feed plants at least once a month with a complete liquid fertilizer containing micronutrients. Many gardeners feed as often as weekly in hot-summer areas where watering is a constant chore. Start feeding in early spring and stop in late summer or early fall to avoid encouraging late growth in frost-prone seasons.
Granular fertilizers can also be used on container plants, but they need time to dissolve before nutrients become available to the roots. A slow-release fertilizer provides nutrients over time, from weeks to months, depending on the product. It can be useful in maintaining a steady supply, but you may need to supplement with liquid fertilizer during peak growth.
As your plants grow, they'll sooner or later run out of root space -- even those well adapted to containers. Without root space, the dense root ball becomes harder to water, causing stunted growth and delayed fruit production. Although it may seem drastic, pruning the roots isn't as hard as it sounds.
Start by pruning the top of the plant by at least one-third to compensate for the roots you are about to prune. Next, remove the plant from the container and cut off one-fourth to one-third (no more than 2 to 3 inches, depending on the size of the pot) of the outside of the root ball with a sharp knife. Then place the plant back in the pot with fresh soil and water thoroughly. If done properly, it can be the easiest way to help out a root-bound plant.
If you keep your subtropical fruit plant outside during the warm months and inside during the winter, you'll need to acclimate your plants to the change in growing environment. If you're putting plants outside after a long winter indoors, do it gradually. Place them in a shady spot first, then slowly expose the plants to increasing amounts of sun over several weeks to help prevent sunburned foliage.
Move plants from outdoors to indoors at an equally slow pace. Give them less and less sun until they're ready to come inside. Before bringing a plant indoors, hose it down to wash off dust or dirt on the leaves. If necessary, spray to control pests, which will multiply when brought indoors.
Once the plants are indoors, they won't need as much water -- but don't allow them to dry out completely. They won't need much light, either, if you are trying to keep plants cool and dormant until spring. But if you are trying to ripen fruit, the more light the better. Consider supplemental illumination with artificial lights. Adjust the feeding according to how you want the plant to grow, but in general feed lightly if at all.
The dry heat that circulates through most homes during the cold months severely shocks plants that have been outside all summer and may cause them to lose their leaves. Do everything possible to increase the humidity around the plants: place the containers on a tray of rocks partially submerged in water; group the plants away from heat vents.