Tree · Rutaceae
Kumquat
Citrus japonica
Give it full sun, even water, and a break from hard frost, and this little citrus keeps fruiting all winter.
Full sun
Every 5–10 days
USDA 8–11
8–15 ft · 2.4–4.6 m
Overview
Think of the kumquat as the little rebel of the citrus family, a small, slow tree that grows thumb-sized fruit you just eat whole. It's from East Asia, and it's happy either in a sunny yard or a big pot you can drag indoors when it gets cold. Here's the fun part, it flips citrus around with a sweet rind wrapped around tart flesh.
So what makes it different from the rest? Mostly its knack for shrugging off cold. A lemon or lime would sulk once things dip below freezing, but a kumquat just rides out a quick chill and keeps its fruit right where it is. That, plus its slow and tidy growth, makes it one of the friendlier citrus for anyone dealing with real winters.
Once it's settled in, it doesn't ask much of you. Sun, steady water, and a feed through the growing season, and that's basically the deal. The one thing to keep an eye on is drainage, because soggy roots cause way more kumquat headaches than the cold ever will.
Care
The short version: full sun, loamy soil that drains fast, and even moisture so the roots never stay wet. Feed it monthly through spring and summer, and give it cover if a hard freeze rolls in.
Light
Give a kumquat full sun, ideally six hours or more a day, and you'll get the heaviest crop and the sweetest fruit. It'll take a little afternoon shade where it's hot, but park it in deep shade and you'll end up with a thin, scraggly tree.
Water
Keep the soil evenly moist, letting the top dry out a touch between waterings, which usually lands around every 5 to 10 days. Heat and pot life dry things out faster, so water more often then, and don't let water pool, because soggy roots are the quickest way to hurt this tree.
Soil
Plant it in loamy, well-draining ground on the acidic side, somewhere around a pH of 6.0 to 6.5. Good drainage matters more than rich soil here, since it's standing water, not poor feeding, that finishes off kumquats.
Temperature
It handles a big range, from about 10°F to 100°F (-12°C to 38°C), which is part of why it's one of the hardier citrus. Even so, it likes a bit of cover during a hard freeze, especially while it's young.
Humidity
Regular air of about 40% to 60% is plenty for a kumquat, so outdoors there's nothing to worry about. Indoors in dry winter heat, though, a little extra humidity keeps the leaf edges from browning.
Feeding
Feed it monthly through spring and summer while it's actively growing, using a balanced citrus fertilizer. Look for one with the micronutrients citrus loves, namely iron, zinc, and manganese, since running short on those is what turns the leaves yellow.
Pruning
Good news, kumquats barely need cutting. Just take out dead, damaged, or crossing branches and any suckers off the rootstock in late winter to early spring once you've picked the fruit.
Repotting
A potted kumquat wants a fresh, bigger container every 2 to 3 years, or sooner if the roots start circling and water shoots straight through. Roots poking out the drainage holes and growth that's stalled are the other signs it's time.
Size & spacing
A kumquat creeps up 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. A pot keeps it on the smaller side, which is part of why it moves indoors so easily.
When to plant
The kumquat's on a slow, cool-season schedule, and it's an easy one to keep track of. It blooms in late spring, around May and June, then takes its sweet time ripening fruit through the colder months, with harvest running from October right into March. Set new trees out in spring once frost's out of the picture.
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
Almost every kumquat issue turns up in the leaves or the fruit, and it usually comes down to water, feeding, or cold. Catch the early signs and you can sort the cause before it gets worse. Find what you're seeing below, then act while it still does some good.
Leaves turning yellow
Yellow leaves are easier to read than they look. Is the yellow only between the green veins? That's a micronutrient thing, usually iron or zinc, while a whole leaf that fades evenly just wants more nitrogen. Soggy, badly drained soil can mimic all of it, so give a chelated citrus feed and let the roots dry out a bit, and you're most of the way there.
Fix:
- Apply a citrus fertilizer with chelated micronutrients
- Correct drainage and reduce watering frequency
Fruit dropping off early
When a kumquat's stressed, it lets its fruit go, and uneven watering is nearly always why, whether the roots are running dry or sitting wet. A cold snap or a big temperature jump can do it too. So take a look back at how you've been watering and what the weather's done, keep the soil evenly moist, and tuck the tree away from frost, and the fruit usually holds.
Fix:
- Maintain consistent soil moisture
- Protect the tree from frost during cold snaps
Black gunk and sticky leaves
That black stuff is sooty mold, and here's the thing, it isn't really the problem. It just grows on the sticky honeydew that sap-sucking bugs leave behind, so flip a few leaves and you'll probably catch soft scale, whiteflies, or aphids underneath. Deal with the bugs using horticultural oil or insecticidal soap, and once they're handled the mold wipes off easily.
Fix:
- Treat the insect pest with horticultural oil or insecticidal soap
- Wash off the mold once pests are controlled
Toxicity
The fruit's a treat for people, but the rest of the tree isn't pet food. The peel, leaves, and stems carry essential oils and psoralens that upset the gut, so a cat, dog, or horse that chews them usually ends up with a mild stomachache. Just keep prunings and dropped fruit picked up wherever animals graze.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Mild
If a cat chews on the peel or a leaf, it'll probably just get an upset stomach, so think drooling, vomiting, and loose stools. Those oils can leave the skin a bit red too.
Dogs Mild
A dog that gnaws the leaves or grabs fallen fruit might act off for a bit, with vomiting, diarrhea, and low energy. Most of the time it's mild and clears up on its own.
Horses Mild
Those same citrus oils and psoralens don't sit well in a horse either, so you'd see colic-like discomfort and loose droppings. Just keep prunings and windfall out of the paddock and you're fine.
Rabbits Caution
A rabbit's gut is pretty delicate, and the oily peel and bitter leaves can easily upset it. So don't hand kumquat over as a snack.
Livestock Caution
Goats, sheep, and cattle can pick at a bit of windfall without much drama, but a big load of oily peel and foliage can sour the rumen and put them off eating. Better to clear the drops away.
Birds Caution
Birds are a little touchy about citrus oils, which can irritate the gut, so it's worth being careful. A small taste of the flesh is okay, but the peel and leaves are off-limits.
People Fruit safe
Good news for anyone with a sweet tooth, the whole fruit, peel and all, is a great snack right off the tree. Cutting up loads of peel or leaves can leave sensitive skin a little irritated, though.
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
You'll only see a few kumquats in gardens and grocery stores, and they mostly differ in shape, sweetness, and how much cold they can take. These are the ones worth knowing by name.
Nagami
Nagami is the one you'll run into most, an oval kumquat that plays tart flesh off against a sweet, edible rind.
Meiwa
Want something to just pop in your mouth? Meiwa is round, bigger, nearly seedless, and sweeter than the others, so it's the best for eating fresh.
Marumi
Marumi is round and a little tart, and it grows on a thorny tree that handles cold better than the rest.
How to propagate
Kumquats come from grafts, cuttings, or seed, and the route you go decides how quickly you get fruit and how closely the tree matches its parent.
GraftingModerate
Spring to early summer when bark slips · 1 to 2 years to a sizable tree
Grafting is how the growers do it, and it makes sense once you see why. Do it in spring or early summer while the bark slips easily, and you'll end up with a tree that's true to the parent, grows fast, and keeps that handy cold tolerance, filling out to 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 they take their time, since they root slowly and unevenly and can need several months to catch. A little rooting hormone and some bottom heat really help stack the odds in your favor.
SeedEasy
Spring · Several years to fruiting
Seed is the easy option, just sow in spring, but it's slow and a bit of a gamble. Seedlings often don't match the parent and can take several years to fruit, so they're mostly good for rootstock or for fun rather than a crop you can count on.
Myths
You should peel a kumquat before eating it because the skin is the bad part.
Nope, a kumquat is that rare citrus you eat skin and all. The rind is the sweet bit and the flesh is the tart bit, which is backwards from an orange, so peeling it just throws away the good part. The peel is totally fine to eat, and honestly it's the point.
Kumquats are too tender to survive any frost.
Not even close, since a kumquat is one of the toughest citrus out there in the cold. It brushes off short dips well below freezing, and sources put its hardiness at around 10°F (-12°C).