Tree · Rutaceae
Key Lime
Citrus × aurantiifolia
Give it full sun, warmth, and free-draining soil, and this thorny little citrus hands you sharp, aromatic limes.
Full sun
Every 5–10 days
USDA 9–11
6–13 ft · 1.8–4 m
Overview
The Key lime is a small, thorny citrus tree, and people grow it for one thing: that tart, deeply fragrant fruit. It made its way to the New World through the Caribbean and took to the Florida Keys so well that the islands ended up naming it. The fruit stays small, only an inch or two across, and it's crammed with seeds and aroma, which is exactly what makes it the lime behind a real Key lime pie.
Here's a nice thing about it: it's everbearing, so it flowers and fruits over a long stretch instead of all at once. The main burst of bloom shows up in spring, and the limes ripen through summer into fall, and you pick them while the skin's still green. Left alone the tree gets to 6 to 13 feet (1.8 to 4 m) tall, but it's happy in a pot and takes pruning well, so you can keep it a lot smaller on a patio or in a bright room.
So what's the catch? Cold, mostly. This tree minds a chill far more than anything else. It wants heat, sun, and soil that drains fast, and it'll shrug off a short dry spell better than most citrus. The bigger thing to watch is disease, since citrus canker and citrus greening have changed where and how you can grow it.
Care
The short version: full sun and warmth, soil that drains freely, and steady moisture once the tree's settled in. Feed it lightly through the growing season, keep it away from frost, and prune only to shape it or hold its size.
Light
Key lime wants full sun, and the more the better if you want good flowers and sweet fruit. It'll put up with partial sun, but the harvest thins out and the canopy gets leggy in the shade. Indoors, just give it the brightest window you've got.
Water
Let the top half of the soil dry out between waterings, which comes out to roughly every 5 to 10 days depending on heat and pot size. It handles a short drought better than most citrus, but it sets the biggest crop with steady moisture. Whatever you do, don't leave it standing in waterlogged soil.
Soil
Go with well-drained loam, silt, or sandy soil, since fast drainage matters more to this tree than just about anything. It's not fussy about pH and grows across a wide 6.0 to 8.0 range. Heavy, soggy ground is the one thing it won't forgive.
Temperature
Key lime is the cold-tender end of citrus and it's happiest in real warmth, comfortable anywhere from 32°F to 100°F (0°C to 38°C) but it takes frost damage at the low end. A hard freeze will kill it, so grow it in the ground only where winters stay mild, and bring container trees inside before the cold hits.
Humidity
This tree likes the air on the humid side, around 50% to 80%. Outdoors in a warm climate, that just takes care of itself. Indoors in dry winter air, group it with other plants or pop it on a pebble tray to lift the moisture around it.
Feeding
Feed it through the spring and summer growing season with a balanced citrus fertilizer that's got micronutrients, and go easy rather than heavy. Citrus tends to run short on minor nutrients, so a feed made for it beats a generic one. Ease off as growth slows for the year.
Pruning
Key lime doesn't ask for much pruning. Take out any dead, damaged, crossing, or low branches and strip off suckers below the graft, since those come from the rootstock, not the lime. Past that, prune only to hold its size or shape it as a container tree.
Repotting
A container Key lime wants a fresh pot every 2 to 3 years. Move it up when you see roots circling the pot or poking out the drainage holes, water running straight through, or growth stalling. Just step up one pot size and refresh the mix, don't drown it in a giant container.
Size & spacing
Left to grow, the tree hits 6 to 13 feet (1.8 to 4 m) tall and spreads 5 to 15 feet (1.5 to 4.5 m) wide. Give an in-ground tree room to fill out, or lean on regular pruning to keep a patio one compact.
When to plant
Key lime goes by warmth, not the calendar. Plant it outside in spring once frost is well behind you, and only in zones 9 to 11 where winters stay mild. It blooms heaviest in spring and gives you green-skinned fruit from summer into fall, and once it's established it'll flower on and off all year.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Late winter to early spring from seed in cold climates; often bought as a grafted nursery tree
- Plant: Spring after all danger of frost has passed; zones 9-11 only
- Harvest: Everbearing; main bloom in spring with fruit ripening summer to fall, picked while still green
Hardiness
USDA hardiness zones: 9–11
Temperature: down to -7°C
Troubleshooting
Most Key lime trouble shows up right on the leaves, twigs, or fruit, and a couple of the worst ones are bacterial diseases with no cure. The trick is knowing a fungus you can prune away from a quarantine disease you have to report. Find what you're seeing below, then act before it spreads to the rest of the tree.
Corky raised spots ringed with yellow on leaves and fruit
Those scabby spots with a yellow ring? That's citrus canker, a bacterial disease that roughs up the leaves, twigs, and fruit and knocks the foliage off. There's no cure, so the plan is to bag the sick growth, spray a copper bactericide, and stick to your local quarantine and reporting rules. Starting with certified trees and keeping water off the leaves is really your best line of defense.
Fix:
- Remove and bag infected leaves, twigs, and fruit
- Apply copper-based bactericide per label
- Comply with local quarantine and reporting rules; there is no cure
Blotchy mottled leaves with small lopsided fruit that stays green
Blotchy leaves and tiny lopsided limes point to citrus greening, or HLB, and this is the big one, the worst thing your tree can catch. A bug called the Asian citrus psyllid spreads it, a lab test confirms it, and once a tree has it, there's just no cure. So the move is to pull and destroy the infected tree, keep the psyllids down, and let your agricultural authority know.
Fix:
- No cure; remove and destroy infected trees
- Control Asian citrus psyllid populations
- Report to local agricultural authority
Young shoot tips dying back with blighted blossoms
If the fresh tips are withering and the flowers are browning, that's usually lime anthracnose, sometimes called withertip, a fungus that goes after shoot tips and new growth. Good news is you can handle it yourself: prune the bad twigs back to healthy wood and hit it with a copper fungicide. Then just open up the canopy for airflow and clear out the deadwood so it doesn't come back.
Fix:
- Prune out affected twigs back to healthy wood
- Apply copper fungicide
- Improve air circulation and remove deadwood
Wilting and dropping leaves while the soil stays soggy
Wilting while the soil is still soaked? That's usually root rot setting in from too much water or drainage that just isn't cutting it. Back off the watering, sort out the drainage, and if it's in a pot, move it into a fresh well-drained mix and snip off the dark, mushy roots. The whole fix really comes down to never letting the tree sit in standing water.
Fix:
- Reduce watering and improve drainage
- Repot into fresh well-drained mix and trim rotted roots
Toxicity
The flesh and juice are perfectly fine for people, but the rest of the tree isn't a pet snack. The peel, leaves, and seeds carry essential oils and psoralens that upset an animal's stomach and can make skin react to sunlight. Keep cats, dogs, and horses away from the foliage and prunings, and wash your own hands after handling fruit if you're heading into the sun.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Mild
If a cat chews the peel or leaves, you'll usually see some drooling, then vomiting, a bit of diarrhea, and a dull, low mood. The oils can leave its skin touchy in the sun too, so keep it in the shade for a bit.
Dogs Mild
A dog that nibbles the foliage or rind tends to get an upset stomach, drool a little, and go flat and listless. It usually stays pretty mild, though those citrus oils can make skin sensitive to sunlight.
Horses Mild
The peel and leaves can hand a horse a sour stomach and a sluggish, off feeling. Honestly, horses don't go looking for citrus, so it's rarely an issue unless prunings end up where they can reach them.
Rabbits Caution
A rabbit's gut just doesn't get along with the aromatic oils in the rind and leaves, so keep every part of the tree out of the hutch. Any trimmings? Off-limits, not a treat.
Livestock Caution
Goats, sheep, and cattle might pick at fallen leaves or fruit, and the citrus oils can leave them with a little digestive upset. It's rarely a big deal, but there's really no reason to let them graze the prunings.
Birds Caution
With the essential oils packed into the peel and leaves, the foliage isn't a great thing to have around birds. A taste of the flesh is a lot less worrying than a beakful of rind or leaf.
People Flesh safe
The flesh and juice? Totally fine, they're a kitchen staple. The catch is the peel oil and sap: handle the fruit or leaves, then head into the sun, and you can end up with a blistering rash called phytophotodermatitis, so wash your hands first.
Lime juice and peel oils combined with sunlight can cause phytophotodermatitis (a blistering skin rash) in people; wash hands and avoid sun exposure after handling fruit or foliage.
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
Key lime doesn't come in a ton of forms, but the few it does are worth knowing before you buy a tree.
Mexican (West Indian) Key lime
This is the real-deal Key lime for an honest Key lime pie, a thorny tree loaded with small 1 to 2 inch fruit that's super seedy and full of aroma.
Thornless Key lime
If you'd rather skip the spines, this nearly spineless one fruits a lot like the original and is way easier to handle and pick.
How to propagate
Here's the cool part: Key lime is unusual for citrus in that its seed comes mostly true to type, so you've got real options, from a free seedling to a grafted nursery tree.
SeedEasy
Spring · 3-6 years to first fruit
Seed is the easy way to go with Key lime, since its seed is largely polyembryonic and comes fairly true to type, which most citrus can't manage. Sow in spring and settle in for the wait, because a seedling takes 3 to 6 years before you get those first limes.
GraftingModerate
Spring to summer · 2-3 years to fruit
Budding or grafting onto a rootstock is what the nurseries do, and for good reason, since it brings disease resistance and steady, even vigor. Do it from spring through summer, and a grafted tree fruits sooner than a seedling, in about 2 to 3 years.
Stem cuttingsModerate
Spring to summer · 1-2 years
Semi-hardwood cuttings taken in spring or summer will root just fine, putting a tree on its own roots within a year or two. It works, but most growers grab seed or grafting first.
Air layeringModerate
Warm season · 1-2 years
Air-layering during the warm season gives you a tree on its own roots in about 1 to 2 years. It's a fine option for citrus, just slower and a bit more fiddly than starting from seed.
Myths
A Key lime is just a small Persian lime.
Nope, they're actually two different species. The Key lime is Citrus x aurantiifolia, while the Persian or Tahiti lime is Citrus x latifolia, which is bigger, seedless, and handles cold better. They look related, but they're not the same fruit.
Citrus is safe for cats and dogs because people eat it.
What's fine on your plate isn't fine in a pet's bowl. The ASPCA lists lime as toxic to cats and dogs, because the peel, leaves, and seeds carry essential oils and psoralens that upset the stomach and can make skin sensitive to sunlight. The fact that you can eat it says nothing about whether it's safe for them.
Key limes grown from seed won't resemble the parent tree.
With most fruit trees that's true, but Key lime is the odd one out. Its seed is largely polyembryonic, so the seedlings come fairly true to type and usually turn out a lot like the tree they came from.