Selecting a Tree.
The simplest way to get going is to buy a Bonsai tree that has already been started, basically a 'pre-bonsai'. A pre started Bonsai, is 'rough material' almost like a blank canvas to start your work of art. This article does not cover training. Training is the essence and art of Bonsai and should be studied and practiced before expecting any great level of success.
In nature, at full maturity kumquats can reach up to 15 feet in height although they average around 7 or 8 feet. Grown in containers they can be trained to a smaller stature, but you'll still be well advised to select either a dwarf or miniature variety.
If selecting a kumquat tree that has already been started, but not from a reputable supplier specializing in bonsai, be aware that nearly all citrus, including Kumquats are grafted trees, quite frequently from a bare root stock of lemons. In most cases you'll be able to clearly see the graft union down towards the trees base.
Being grafted does not exclude the tree from being used as a bonsai but it does detract from its overall long term value. Grafting is commonly used by Bonsai artists, branch grafting, bud grafting, thread grafting, but rarely root stock grafting.
You'll only need one tree to start - kumquats 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.
Containers - The pot the kumquat is in should be large enough to allow just a little room for root expansion. Not too much room just a little if you hope to keep it miniaturized. Citrus does not always respond well to being containerized so this can at times be an issue. Needless to say it should have a base tray to catch excessive water and adequate drainage holes
Starting from Cuttings or Seeds - A more rewarding method, in the long run, is to plant and cultivate your own tree from cuttings or seeds. This method can be tediously slow, taking anywhere from 3 - 5 years before you can begin training the tree. During this time you can study up on training techniques and methodology.
In the trees early stages, it should be kept in moist soil, not a swamp, don't drown it, just keep the soil moist. A thin layer of organic mulch at the trees base will help in retaining moisture. Keep a small circle clear of mulch around the base, persistent direct contact with damp mulch is not advisable.
Humidity - If indoors for extended periods, under forced artificial heat, it may become necessary to provide added humidity. Humidity Trays are helpful, they are simply shallow trays filled with a layer of gravel and water which will help provide needed moisture. As it evaporates the water vapor increases the humidity lost to forced dry air of modern heating systems.
Other modes of increasing Humidity include.1. Humidifiers.
2. Clustering your plants. All Plants exhale moisture through their leaves in a process known as transpiration, By grouping your kumquat with other indoor plants you enhance their environment.
3. Misting the trees foliage with a simple spray bottle is helpful but not a cure all
Water - Water until it begins to trickle out of the holes at the containers base. It needs to be watered generously, but not to the point of perpetual saturation. Root rot and fungal infestations are not unheard of and excessive watering can increase the odds of these problems occurring.
Light - Citrus needs a lot of light, some varieties 12 - 16 hrs. a day, kumquats a tad less and just a tad. Indoors they should be kept on or near a sunny window preferably a southern exposure. Kumquat trees thrive in full sunlight, whether you plan on placing your tree[s] outdoors or indoors a sun drenched location is best.
Grow Lights are an option, modern horticultural lighting can provide sufficient full spectrum light to help keep bonsai and most indoor plants healthy.
Temperature - During extreme cold spells they should most certainly be kept warm and a windowsill is not necessarily the warmest spot available.
They do not fare well in temperatures below 45 F, bringing them indoors at night is advisable unless you live in a subtropical zone. Although they have been known to withstand temperatures as low 20 F, when average outdoor temperatures start approaching the 50 F range - it's a good idea to bring them indoors for the winter. They are suitable for year round placement outdoors only in USDA zones 9 and 10.
Fertilizers for kumquats should be used at roughly half their recommended dosage. It should be applied monthly during the active growing season and not at all during the winter months. Bonsai has been demonstrated to respond well to foliar feeding, with a water-soluble fertilizer.
It's okay to a little additional fertilizer every so often, but don't get carried away. Excessive fertilizer can do more harm than good. Fertilizer developed specifically for citrus trees is naturally a good choice.
Pests- Kumquats are susceptible to spider mites, mealy bugs and scale. Check the trunk regularly. Misting the foliage periodically will help not only add moisture but reduce dust. Dust will attracts pests, they hide themselves and deposit egg clusters in the dust while parasitizing the plant .
How to Grow Kumquats