Tree · Rutaceae
Kumquat
Citrus japonica
Give it full sun, even water, and shelter from hard frost, and this little citrus fruits right through winter.
Full sun
Every 5–10 days
USDA 8–11
8–15 ft · 2.4–4.6 m
Overview
The kumquat is the small, bold cousin of the citrus family, a slow-growing tree that carries thumb-sized fruit you eat whole. It comes from East Asia and earns its keep in a sunny yard or a big pot, staying compact enough to move under cover when the cold rolls in. The fruit flips the usual citrus on its head, with a sweet rind wrapped around tart flesh.
What sets it apart from other citrus is its toughness in the cold. Where a lemon or lime sulks below freezing, a kumquat shrugs off a brief dip and keeps its fruit hanging on the branch. That hardiness, plus its slow, tidy growth, makes it one of the easier citrus to keep in a region with real winters.
Care is light once the tree is settled. Give it sun, steady water, and a feed through the growing season, and it asks for little else. The main thing to watch is drainage, since soggy roots cause more kumquat trouble than the cold ever will.
Care
The short version: full sun, loamy soil that drains fast, and even moisture without letting the roots stay wet. Feed monthly through spring and summer, and shelter the tree from a hard freeze.
Light
Give a kumquat full sun, ideally six or more hours a day, for the heaviest crop and the sweetest fruit. It will take light afternoon shade in a hot climate, but deep shade leaves you with a thin, sparse tree.
Water
Keep the soil evenly moist and let the top dry slightly between drinks, watering roughly every 5 to 10 days. Heat and container life dry the roots faster, so step up the frequency then, and make sure water never pools, because soggy roots are the quickest way to harm this tree.
Soil
Plant in loamy, well-draining ground on the acidic side, around a pH of 6.0 to 6.5. Sharp drainage matters more than richness here, since standing water is what kills kumquats.
Temperature
The tree handles a wide range, from about 10°F to 100°F (-12°C to 38°C), which makes it one of the hardier citrus. It still appreciates shelter during a hard freeze, especially when young.
Humidity
Average air around 40% to 60% suits a kumquat fine, so there's no number to fuss over outdoors. Indoors in dry winter heat, a little extra humidity keeps the leaf edges from browning.
Feeding
Feed monthly through spring and summer while the tree is actively growing, using a balanced citrus fertilizer. Look for one that carries the micronutrients citrus craves, namely iron, zinc, and manganese, since a shortage of these is what turns the leaves yellow.
Pruning
Kumquats need very little cutting. Take out dead, damaged, or crossing branches and any suckers from the rootstock in late winter to early spring after the harvest wraps up.
Repotting
A potted kumquat wants a fresh, larger container every 2 to 3 years, or sooner if the roots start circling and water races straight through. Roots poking from the drainage holes and stalled growth are the other tells that it's time.
Size & spacing
A kumquat grows slowly to about 8 to 15 feet (2.4 to 4.5 m) tall with a 6 to 10 foot (1.8 to 3 m) spread. Containers keep it on the smaller end, which is part of why it travels indoors so well.
When to plant
The kumquat runs on a long, cool-season clock. It blooms in late spring around May and June, then ripens its fruit slowly through the colder months, with the harvest stretching from October all the way into March. Set new trees out in spring once the danger of frost has passed.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Spring, after danger of frost has passed
- Harvest: Blooms late spring (May to June); fruit ripens October through March
Hardiness
USDA hardiness zones: 8–11
Temperature: down to -12°C
Troubleshooting
Most kumquat problems show up in the leaves or the fruit, and they trace back to water, feeding, or cold. Read the early signs and you can fix the cause before it spreads. Match what you see below, then act while it still helps.
Leaves fading to yellow
When the leaves pale, look first at whether the yellow sits between green veins or covers the whole leaf. Interveinal yellowing points to a shortage of iron, zinc, or another micronutrient, while an even fade usually means the tree is short on nitrogen. Soggy soil and poor drainage cause the same look, so feed with a chelated citrus fertilizer and ease off the water until the roots dry out.
Fix:
- Apply a citrus fertilizer with chelated micronutrients
- Correct drainage and reduce watering frequency
Fruit dropping early or never setting
A kumquat sheds its fruit when it's stressed, and uneven watering is the usual culprit, whether the roots stay too dry or sit waterlogged. A cold snap or a sharp swing in temperature does the same thing. Check your recent watering and the weather, keep the soil evenly moist, and shelter the tree when frost threatens.
Fix:
- Maintain consistent soil moisture
- Protect the tree from frost during cold snaps
Black soot and a sticky film on the leaves
The black coating is sooty mold, and it grows on the sugary honeydew that sap-sucking insects leave behind. Turn a few leaves over and you'll usually find soft scale, whiteflies, or aphids feeding underneath. Treat the bugs with horticultural oil or insecticidal soap, and once they're gone you can wash the mold off.
Fix:
- Treat the insect pest with horticultural oil or insecticidal soap
- Wash off the mold once pests are controlled
Toxicity
The fruit is a treat for people, but the rest of the tree is not for pets. The peel, leaves, and stems hold essential oils and psoralens that irritate the gut, so a cat, dog, or horse that chews them tends to get a mild upset stomach. Keep prunings and fallen fruit picked up where animals graze.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Mild
A cat that chews the peel or leaves usually gets an upset stomach, with drooling, vomiting, and loose stools. The essential oils can also leave the skin red or irritated.
Dogs Mild
Expect vomiting, diarrhea, and a dull, low mood if a dog gnaws the leaves or fallen fruit. Most cases stay mild and pass on their own.
Horses Mild
The same citrus oils and psoralens upset a horse's gut, bringing on colic-like discomfort and loose droppings. Keep prunings and windfall out of the paddock.
Rabbits Caution
A rabbit's gut is delicate, so the oily peel and bitter leaves can throw off its digestion. Don't offer kumquat as forage.
Livestock Caution
Goats, sheep, and cattle may nibble fallen fruit without much harm, but a large helping of oily peel and foliage can sour the rumen and put them off their feed.
Birds Caution
Birds are touchy about citrus essential oils, which can irritate the gut. A small taste of the flesh is fine, but keep them away from peel and leaves.
People Fruit safe
The whole fruit, peel and all, is good to eat and a kitchen favorite. Handling lots of cut peel or leaves can leave sensitive skin a little irritated.
The fruit flesh is edible to people, but pets chewing peel, leaves, or large amounts of plant material can get mild GI irritation; essential oils may also irritate skin.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
Only a few kumquats turn up in gardens and groceries, and they differ mostly in shape, sweetness, and how much cold they take. These are the ones worth knowing by name.
Nagami
The most widely grown kumquat, with oval fruit that pairs tart flesh against a sweet, edible rind.
Meiwa
A round, larger, nearly seedless fruit that runs sweeter than the rest and is the best one for eating fresh.
Marumi
A round, slightly tart fruit carried on a thorny tree that handles cold better than most.
How to propagate
Kumquats are grown from grafts, cuttings, or seed, and the method you pick decides how fast you get fruit and how true it runs to the parent.
GraftingModerate
Spring to early summer when bark slips · 1 to 2 years to a sizable tree
Grafting is the standard commercial way to make new kumquats, and for good reason. Done in spring or early summer while the bark slips easily, it gives you a true-to-type tree that grows fast and holds the parent's cold tolerance, reaching a sizable tree in 1 to 2 years.
Stem cuttingsModerate
Late spring to summer · Several months to root
You can root cuttings taken in late spring or summer, but be patient, because they root slowly and unevenly and can take several months to take hold. Rooting hormone and a little bottom heat tip the odds in your favor.
SeedEasy
Spring · Several years to fruiting
Seed is the easy route, sown in spring, but it's a slow and uncertain one. Seedlings often don't come true to the parent and can take several years to bear, so they're used mostly for rootstock or for fun rather than a reliable crop.
Myths
You should peel a kumquat before eating it because the skin is the bad part.
A kumquat is the rare citrus you eat whole. The rind is the sweet part and the flesh is the tart part, the reverse of an orange, so peeling throws away the best of it. The peel is harmless to people and meant to be eaten.
Kumquats are too tender to survive any frost.
Kumquat is among the toughest of all citrus in the cold. It shrugs off brief dips well below freezing, with sources reporting hardiness down to about 10°F (-12°C).