Kumquats is a strange fruit; they're like oranges but smaller and sour. It is possible, and perhaps even preferable, to grow kumquat in a large container as a patio plant, and you can even successfully grow them inside under the right conditions. They can also be grown as delightful little bonsai, with tiny fruit no larger than a pinkie nail. To grow them successfully, follow the same general rules you would for growing oranges and other citrus: good drainage, plenty of water and sunshine, and a quality fertilizer.
- Light: Kumquat thrive in bright light, even direct sunlight if possible. During the summer, consider moving the plant outdoors to a sunny patio or balcony, where they can get full sun all day. Full sun encourages healthy growth, discourages leaf mold and fungus, and encourages flowering.
- Water: No citrus likes "wet feet," and kumquat is no exception. They do best when the rootball is planted slightly higher than the soil surface and they are watered regularly, but their drainage is immaculate. Water regularly and do not let the soil dry out.
- Fertilizer: A high-quality citrus fertilizer will encourage healthy growth and flowering. Fertilize at the beginning of the growing season.
- Soil: Any good quality potting mix will do, but make sure there's plenty of structure to encourage good drainage. Repot plants in old, sandy or mucky soil.
Kumquat can be propagated by leaf tip cutting or branch cutting. A rooting hormone will increase your odds of success. Take the cuttings early in the growing season, dip them into rooting hormone, then plant into a quality potting mix. Place the cutting in a warm, bright place and wait for new growth to emerge. Don't try to propagate your kumquat from seed.
Kumquat should be repotted annually or biannually for the first few years. The mature tree will be about 5 or 6 feet tall, depending on your pruning. Plants will not fruit for the first few years of their lives and they will grow slowly. When repotting, be careful not to disturb the roots and place into one size larger pot. If the tree is too large to repot, carefully scrape away as much topsoil as possible and replace it with new potting soil. Try to loosen the soil further down to increase drainage, using a tool or stick of some variety.
The kumquat has been extensively hybridized over the years and there are a number of varieties. They range in color from pale orange fruit to a deep red fruit, depending on the variety. Choose your variety based on the fruit. Any variety can be successfully trained into a bonsai.
Kumquats have been in cultivation throughout Asia for centuries, and they are perfectly adapted to container culture. They are fairly cold-hardy and can withstand temperatures down to freezing for brief periods. The main trick with successful citrus is to avoid letting the plant sit in any kind water. This is a common mistake new growers make, thinking their subtropical citrus plants like lots of water. In fact, they do like lots of water but cannot tolerate sitting in water for any period of time. A healthy kumquat will yield dozens of fruit throughout the late summer and fall. Wait until the skins pick up a deep color and the fruit are slightly soft to the touch before harvesting. Once harvested, kumquat will last a relatively long time. They can be eaten out of the hand or made into jams or jellies. Kumquat is vulnerable to mealybugs and aphids.