Gadenin日本語Get the appThe one citrus that wants a small pot
Every other citrus you grow in a container is being tolerated by the pot. A kumquat is not. It is naturally small leaved, slow growing and shallow rooted, and it crops properly in a container that would leave a lemon starved and a grapefruit dying. That single fact changes how you plant one: you are not aiming to get it into the biggest pot you can lift, you are aiming to keep it in a pot you can move with one hand for as long as possible.
A young grafted tree with a rootball six to eight inches (15-20 cm) across goes straight into a 10 to 12 inch (25-30 cm) pot. Step up two inches (5 cm) of diameter every second or third year and stop at about 14 to 16 inches (35-40 cm). That is a working ceiling, not a stage on the way to something larger. A mature kumquat in a 16 inch pot will carry several hundred fruit in a good year, and the whole thing still weighs under 60 pounds (27 kg) wet.
Resist the urge to over-pot a small tree. A rootball sitting in the middle of a large volume of wet compost is the single most common way a kumquat is killed in its first year. The roots cannot dry the outer compost, that compost goes sour, and the tree drops its leaves in slow motion over a winter while the owner waters it more.
| Stage | Pot diameter | Typical rootball | Move on when |
|---|---|---|---|
| First pot from the nursery | 10-12 in (25-30 cm) | 6-8 in (15-20 cm) | Roots circle the base after 2-3 years |
| Second pot | 12-14 in (30-35 cm) | 10 in (25 cm) | Water runs straight through in summer |
| Final pot | 14-16 in (35-40 cm) | 12 in (30 cm) | Do not move on; root prune instead |
| Open ground, mild climate only | n/a | n/a | Winter lows stay above 20F (-7C) |
A gritty mix that drains in seconds
Kumquat roots are fine and shallow and they rot faster than they dry. Do not use a bagged multipurpose or peat-based potting mix on its own; it holds water in the lower third of the pot exactly where the roots cannot use it. Build a mix instead, roughly two parts of a loam-based or bark-based compost, one part coarse grit or perlite, and one part composted bark chips of about a quarter inch (6 mm).
The test is simple. Fill the pot, water it hard, and count. Water should be running from the drainage holes within five seconds and should stop within a minute. If it pools on the surface for more than a few seconds, add more grit and start again. It is far easier to fix this now than to unpot a fruiting tree in three years.
Kumquats prefer a slightly acid root zone, around pH 6.0 to 6.5. Hard tap water pushes a pot alkaline over a few seasons and shows up as pale leaves with green veins. Collect rainwater where you can, and if you cannot, plan on refreshing the top two inches (5 cm) of compost every spring.
Never put a layer of gravel or broken pot in the bottom for drainage. It raises the level of the saturated zone rather than lowering it, and in a shallow-rooted tree that costs you the roots that matter most.
Plant high, keep the graft clear
Almost every kumquat sold is grafted, usually onto a trifoliate or flying dragon rootstock, and that graft union is the reason the tree is hardy and compact. Buried, it will either rot or throw roots from the scion and lose you both traits. The union is the visible kink or change of bark texture low on the stem; it must stay two inches (5 cm) clear of the compost surface for the life of the tree.
- Water the tree before you unpot it A dry rootball crumbles and tears the fine feeding roots as it comes out. Soak it an hour ahead and let it drain, then the whole ball slides out intact.
- Tease only the outer half inch Loosen circling roots around the outside and the base with your fingers. Do not wash the rootball off or cut into the core; kumquats sulk for a season after root disturbance far more than a lemon does.
- Set it proud of the rim Position the top of the rootball about an inch (2.5 cm) above the eventual compost surface, so it settles level or slightly high. Backfill around it and firm with your fingers, not your weight.
- Water once, then wait Water thoroughly to settle the mix, then do not water again until the top two inches (5 cm) are dry. A newly potted tree has no roots out in the fresh compost and cannot use it yet.
- Strip the flowers for one season If a newly planted tree flowers in its first late summer, pinch the flowers off. You lose one small crop and gain a root system that will carry heavy crops for a decade.
Where to stand it, and what to write down
Stand it in the brightest position you have, with at least six hours of direct sun through the growing season. Kumquats color and sweeten on light, and a tree in half shade makes fruit that stays sharp and pale. Shelter it from constant wind, which shreds the small leaves and dries a small pot alarmingly fast.
Put the pot on a wheeled caddy from day one even though it is light. You will be moving this tree several times a year and a caddy means you do it without thinking about it. Raise it on feet so the drainage holes never sit in a saucer of water.
Write down the date you potted it, the pot diameter, and the mix you used. Add a line for the position of the graft union relative to the compost. Three years later, when you are deciding whether to pot on or root prune, those three facts tell you more than looking at the tree does.