Growing dwarf citrus as houseplants offers tantalizing rewards: glossy foliage, fragrant flowers and colorful, edible fruit. But truth be told, growing any fruiting plant indoors can be a challenge. The best way to raise these beautiful trees outside their normal range is to grow them indoors during winter and outdoors for summer.
If citrus isn't sold locally, search out online mail-order suppliers. Select dwarf plants, ideally grafted on Flying Dragon rootstock. Dwarf trees usually grow 3-5 feet tall when planted in pots. Most dwarf trees aren't on Flying Dragon.
Container: Choose a lightweight pot to make moving it easier (or set it on a wheeled platform). Grab a 10-12-inch container for a 1-year-old tree; a 14-16-inch pot for a 2-3-year-old tree. Avoid planting a small tree in an overly large pot. Make sure the pot has drainage holes.
Soil: Use a packaged commercial, lightweight growing mix without water-absorbing crystals.
Light: For healthiest growth and fruiting, citrus trees need 8-12 hours of sun daily (a cool greenhouse is ideal). In northern climates, place a tree in a south- or southwest-facing window to provide light in winter. Supplement with grow lights as needed.
Water: Citrus don't like the soil too wet or too dry. Water thoroughly, and then allow the soil to partially dry, but don't let trees wilt. Never let pots sit in standing water.
Humidity: Lack of humidity in winter is one of the biggest challenges to growing citrus indoors. Mist plants, use a humidifier or set pots above water-filled trays. Keep plants away from heaters or cold drafts.
Fertilizer: If possible, use a citrus fertilizer that contains micronutrients iron, zinc and manganese. Most organic citrus fertilizers lack micronutrients; seaweed fertilizer can supply missing micronutrients. With all fertilizers, follow label instructions. During the indoor season, fertilize trees at half-strength.
Flowers and fruit: Citrus normally flower most heavily in spring, but it's not uncommon for plants to have at least some open blooms at any given time throughout the year. Citrus trees often carry flowers and ripening fruit at the same time. Blossoms rely on wind for pollination. Indoors, give trees a good shake to shift pollen. Some people even go as far as to transfer pollen from one flower to another with a small artist's brush.
Don't allow fruit to ripen during the first year of growth so that plants direct energy to establishing healthy branch and root systems. Fruits require 6-12 months to mature, depending on type. When is fruit ripe? Heaviness and deep color are good indicators of ripeness, but taste-testing is the best gauge.
Pruning: Prune branches at any point in the year to shape the tree and help limit overall size. Another way to limit size and prevent the tree from becoming rootbound is to slip the plant from its pot and prune a few inches from the rootball every 3-5 years. At the same time, add fresh soil to the pot.
Annual Moves: When spring temperatures stay reliably above 40ºF, move citrus outside. Acclimate plants to outdoor conditions by setting them in a shady, sheltered spot for a few hours a day. Gradually work up to leaving plants outside overnight. Follow the same principles used to harden off seedlings. Similarly, about two weeks before the autumn transition indoors, set the tree in a shady spot to prepare it for lower interior light levels.
Types of Citrus
Acidic citrus produce on normally smaller trees adapt best to container culture in interior conditions. Good choices to try include:
- Meyer Lemon: bears large, sweet-tart lemons year-round
- Calamondin Orange: sour fruit with sweet skin; makes wonderful marmalade
- Dwarf Bearss Lime: seedless, large fruits ripen in winter and early spring
- Kaffir Lime: fragrant leaves and fruit zest used in Thai cooking
- Kumquat: bears 1.5-inch-long sweet, orange fruits in fall