Tree · Rutaceae
Kumquat
Citrus japonica
Give it full sun, steady water, and cover from hard frost, and this little citrus will happily fruit right through winter.
Full sun
Every 5–10 days
USDA 8–11
8–15 ft · 2.4–4.6 m
Overview
The kumquat is a gentle place to start with citrus, a small, slow-growing tree that hands you thumb-sized fruit you can pop in your mouth whole. It hails from East Asia and settles in happily in a sunny corner of the yard or a roomy pot you can shift indoors when the cold arrives. Best of all, it flips citrus around, wrapping a sweet rind around tart flesh.
What makes it so forgiving is its easygoing toughness in the cold. Where a lemon or lime would sulk once the temperature drops, a kumquat rides out a brief chill and keeps its fruit on the branch. That calm hardiness, paired with its slow and tidy habit, makes it one of the kindest citrus to grow where winters actually bite.
Once it has settled in, this tree asks very little of you. Offer sun, even water, and a monthly feed through the growing months, and you have done nearly all it needs. The one thing worth minding is drainage, since wet roots trip up far more kumquats than any frost ever could, and that is an easy thing to get right.
Care
The short version: give it full sun, loamy soil that drains fast, and even moisture without leaving the roots soggy. Feed monthly through spring and summer, and cover the tree if a hard freeze is coming.
Light
Set your kumquat where it gets full sun, ideally six hours or more each day, and it will reward you with the heaviest, sweetest crop. A little afternoon shade is fine in a hot spot, though deep shade will leave you with a thin, sparse tree.
Water
Keep the soil evenly moist, letting the top dry a touch between drinks, which usually works out to about every 5 to 10 days. Heat and pot life dry things faster, so water more often then, and always let it drain freely, because soggy roots are the fastest way to set the tree back.
Soil
Give it loamy, well-draining ground on the acidic side, near a pH of 6.0 to 6.5. Sharp drainage counts for more than rich soil here, since it is standing water, not poor feeding, that undoes a kumquat.
Temperature
This tree copes with a wide swing, roughly 10°F to 100°F (-12°C to 38°C), which makes it one of the more forgiving citrus. Even so, it welcomes a little cover in a hard freeze, especially while it is young.
Humidity
Ordinary air of about 40% to 60% keeps a kumquat perfectly content, so outdoors there is nothing to fret over. Inside during dry winter heat, a bit of added moisture helps keep the leaf edges from browning.
Feeding
Feed once a month through spring and summer while the tree is growing, using a balanced citrus fertilizer. Choose one carrying the micronutrients citrus loves, namely iron, zinc, and manganese, since it is a shortage of these that yellows the leaves.
Pruning
Happily, a kumquat needs almost no cutting. Just tidy out dead, damaged, or crossing branches and any suckers from the rootstock in late winter to early spring once the harvest is done.
Repotting
A potted kumquat likes a fresh, roomier home every 2 to 3 years, or sooner if roots begin circling and water rushes straight through. Roots peeking from the drainage holes and growth that stalls are your other gentle hints that it is time.
Size & spacing
Your kumquat climbs slowly to around 8 to 15 feet (2.4 to 4.5 m) tall with a 6 to 10 foot (1.8 to 3 m) spread. A container keeps it toward the smaller end, which is part of why it moves indoors so easily.
When to plant
The kumquat keeps a slow, cool-season rhythm, and it is an easy one to follow. It flowers in late spring around May and June, then takes its time ripening fruit through the chilly months, with the harvest reaching from October right into March. Plant new trees out in spring once frost is safely behind you.
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
Nearly every kumquat hiccup shows up in the leaves or the fruit, and it usually traces back to water, feeding, or cold. The reassuring part is that the early signs are easy to read, so you can settle the cause before it grows. Find what you are seeing below and act while a small nudge is all it takes.
When the leaves start to go yellow
Take heart, because yellow leaves are one of the easiest things to read and put right. If the yellow sits between green veins, your tree is simply hungry for a micronutrient like iron or zinc, and if the whole leaf pales evenly it usually wants more nitrogen. Wet, poorly drained soil can fake the same look, so offer a chelated citrus feed and let the roots dry a bit, and the color tends to come back.
Fix:
- Apply a citrus fertilizer with chelated micronutrients
- Correct drainage and reduce watering frequency
Fruit falling too soon or not forming
It feels discouraging when the little fruits drop, but the cause is almost always something you can steady. Uneven watering is the most common reason, so roots that swing between too dry and too soggy will let the fruit go, and a cold snap can as well. Look back at your recent watering and the weather, aim for soil that stays evenly moist, and tuck the tree out of the frost, and it should hold on.
Fix:
- Maintain consistent soil moisture
- Protect the tree from frost during cold snaps
A black film and sticky leaves
Don't panic if the leaves look dusted with black, because this sooty mold is more of a nuisance than a real threat. It settles on the sweet honeydew left by tiny sap-feeders, so flip a few leaves and you will likely spot soft scale, whiteflies, or aphids hiding below. Clear the insects gently with horticultural oil or insecticidal soap, and once they are gone the mold wipes right 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 joy for you, but the rest of the tree is not a snack for pets. Its peel, leaves, and stems carry essential oils and psoralens that upset the stomach, so a cat, dog, or horse that chews them tends to feel mildly queasy for a bit. A quick sweep of prunings and windfall where animals graze keeps everyone comfortable.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Mild
If your cat nibbles the peel or a leaf, the worst you will usually see is a queasy stomach, with some drooling, vomiting, or loose stools that soon settle. The oils can leave a little skin redness too, so a quick tidy-up of trimmings keeps things easy.
Dogs Mild
A dog that chews the leaves or windfall fruit may seem off for a day, with vomiting, diarrhea, and a low mood. The good news is that most cases stay gentle and clear up on their own.
Horses Mild
The citrus oils and psoralens unsettle a horse's gut in the same way, so you might see colic-like discomfort and soft droppings. Sweeping prunings and dropped fruit out of the paddock keeps them comfortable.
Rabbits Caution
A rabbit has a sensitive tummy, and the oily peel and bitter leaves can throw its digestion off balance. To be safe and kind, simply skip kumquat as a treat.
Livestock Caution
Goats, sheep, and cattle can pick at a little fallen fruit without much fuss, but a big mouthful of oily peel and foliage may sour the rumen and dull their appetite. A little tidiness spares them the trouble.
Birds Caution
Birds are a bit delicate with citrus oils, which can irritate the gut, so play it safe. A small taste of the flesh is fine, though the peel and leaves are best kept out of reach.
People Fruit safe
Good news for you: the whole fruit, peel and all, is a lovely and safe snack straight off the tree. If you handle a lot of cut peel or leaves, sensitive hands may feel a touch of irritation.
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 handful of kumquats reach gardens and grocery shelves, and they mostly differ in shape, sweetness, and how much cold they can take. These are the few worth knowing by name.
Nagami
You will meet Nagami most often, an oval kumquat that sets tart flesh against a sweet, edible rind.
Meiwa
If you want the friendliest one for eating fresh, reach for the round, larger, nearly seedless Meiwa, which runs sweeter than the others.
Marumi
Marumi gives you a round, slightly tart fruit on a thorny little tree that takes the cold better than most.
How to propagate
You can raise kumquats from grafts, cuttings, or seed, and the route you choose decides how soon 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 pros make new kumquats, and it is a reassuring choice for you too. Do it in spring or early summer while the bark slips freely, and you get a tree that stays true to the parent, grows briskly, and holds that lovely cold tolerance, filling out to a sizable tree in 1 to 2 years.
Stem cuttingsModerate
Late spring to summer · Several months to root
Cuttings taken in late spring or summer will root, so long as you give them time, since they come along slowly and unevenly and may need several months to take hold. A dip of rooting hormone and a bit of warmth beneath them nudge things your way.
SeedEasy
Spring · Several years to fruiting
Sowing seed in spring is the simplest path and a fun one, even if it asks for patience. Seedlings often do not match the parent and may take several years to fruit, so treat them as rootstock or a happy experiment rather than a sure crop.
Myths
You should peel a kumquat before eating it because the skin is the bad part.
Here is a happy surprise: a kumquat is meant to be eaten whole. The sweet part is the rind and the tart part is the flesh, just the opposite of an orange, so peeling it tosses out the best bite. You can eat the peel with confidence, and you are supposed to.
Kumquats are too tender to survive any frost.
You can relax about the cold, because a kumquat is one of the toughest citrus there is. It brushes off short spells well below freezing, and sources put its hardiness down to about 10°F (-12°C).