Kumquats are a tiny citrus, similar to oranges in taste but oblong and about the size of a cocktail olive. They have some advantages for gardeners in cooler regions in that they will grow in areas that Oranges and other citrus will not.
The fruit is sweet with a hint of tartness and doesn't need to be peeled, the skin is thin enough that the whole kumquat can be popped into your mouth and salavatiously devoured in one bite.
Kumquats are not plants that you would dump into some dirt and hope for the best. They do require some tender loving care. The tree itself is considered an evergreen and hails from the Orient. At full maturity, under prime conditions, they can reach up to 15 feet in height but generally average around 7 or 8 feet. Grown in containers they can be trained to a smaller stature.
Full sun is best, a little shade ain't gonna kill it, but they do best in full sun. They will tolerate a wide range of soil acidity and have been proven to grow in almost any pH, however a soil pH range between 5.5 and 6.5 is optimal.
Grown outdoors in soil they are hardy in USDA zones 9 and 10 although they have been successfully propagated a tad further North. They ain't gonna grow on the arctic circle but will survive in areas such as Virginia and Northern California. They can withstand winter temperatures as low as 18 - 20 F. and will also grow by the seaside which many other citrus will not. As a potted plant they can be grown anywhere and moved indoors or outdoors as the weather dictates.
The trees are self pollinating / self fertile, so one tree is all that is needed to produce kumquats. Multiple trees are always better for genetic diversity, but not essential.
In the trees early stages, it should be kept in moist soil, not saturated. Not a swamp, don't drown it, just keep the soil evenly moist. A thin layer of organic mulch at the trees base will help in retaining moisture. Keep a small circle clear of mulch, persistent direct contact of mulch with the tree is not advisable.
Do not fertilize the baby kumquat tree till it is several months old, once you start fertilizing, do so in moderation. Kumquats like all citrus trees are heavy feeders and will benefit from a moderately nitrogen rich soil but also require micro nutrients and trace minerals - managanese and magnesium, iron, copper, boron and zinc. Once the tree is established fertilizer should be applied in moderation every other month. Foliar sprays or conventional soil fertilizer will suffice, but it is best that if you use a commercial blend that is designed specifically for citrus trees. Reduce or do not apply fertilizer in late fall when winter is approaching.
As a young plant it is a good idea to pinch back the new growth tips and soft shoots which will lead to a fuller and bushier tree.Pruning is only necessary to remove dead branches and suckers or to train the tree to a desired shape or height. If pruning for shape or height it is best to wait till after the harvest. Older plants may need to be pruned only to maintain shape and this is best done after fruiting.
Many kumquat trees are grafted , when these kumquat plants are young, shoots at times will develop below the graft union. These shoots should be removed lest they commandeer the rootstock leaving the grafted kumquat small, scraggly and unproductive.
One of the primary reasons that kumquat trees fail is root rots. That is the main reason, as we advised earlier on, that excess moisture should be avoided. You should also keep mulch from coming in direct contact with the base of the tree, a small clear circle at the trunk base is a nifty idea.
Containers should have more drainage than normal, drill some holes if need be. Air circulation is also advisable, moisture is not only soil borne - it is air borne so ample ventilation / air circulation is advisable.
Aphids and spider mites will atatck any plant and kumquats are on their menu. Snails and slugs on occasion will chow down on the foliage, but they are rarely a major issue. Leaf rollers - from timwe to time will appear on kumquat trees but are also seldom a major issue. Scales can be a general nuisance. If scales are detected and natural organic methods of control fail, Neem is the most effective control for scales and ecologically sound as well.
Citrus does not lend itself well to being root bound or 'pot-bound', in fact that is why you'll rarely see bonsai as a citrus plant, Kumquats are no exception. They can be grown successfully in containers, but you'll need a relatively large container with more than ordinary drainage holes. Once the tree is established, elevating it slightly off the ground is advantageous not only for drainage but air circulation as well.
If you live in a zone where it isn't necessary to move the trees indoors in cool weather, it would be advisable to provide some protection for the semi-exposed roots that the containers facilitate. Some plastic or even a blanket should suffice.