Tree · Rutaceae
Key Lime
Citrus × aurantiifolia
Give it full sun, warmth, and free-draining soil, and this thorny little citrus fires back 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 that earns its place with tart, deeply fragrant fruit. It traveled to the New World through the Caribbean and took to the Florida Keys so completely that the islands handed it their name. Each lime stays small, only an inch or two across, yet it packs a wallop of seeds and aroma, which is exactly what makes it the lime that powers a real Key lime pie.
It fruits as an everbearing tree, so it flowers and sets limes across a long season instead of firing off one quick crop. The main flush of bloom breaks in spring, and the limes ripen through summer into fall, picked while the skin still glows green. Let it run and the tree climbs to 6 to 13 feet (1.8 to 4 m) tall, but it thrives in a pot and takes pruning in stride, so you can hold it far smaller on a patio or in a bright room.
Cold is the one thing that stops this tree cold. It craves heat, sun, and soil that drains fast, and it powers through a short dry spell better than most citrus. The real challenge to plan around is disease, since citrus canker and citrus greening have reshaped where and how you can grow it.
Care
The short version: load it up with full sun and warmth, plant it in soil that drains freely, and keep the moisture steady once the tree digs in. Feed it lightly through the growing season, guard it from frost, and prune only to shape it or hold its size.
Light
Key lime chases full sun, and the more it drinks in, the harder it flowers and the sweeter the fruit ripens. It gets by in partial sun, but the harvest thins and the canopy stretches in the shade. Indoors, plant it in front of the brightest window you have.
Water
Let the top half of the soil dry out between waterings, which lands at roughly every 5 to 10 days depending on heat and pot size. The tree shrugs off a short drought better than most citrus, yet it sets its biggest crop with steady moisture. Just never leave it standing in waterlogged soil.
Soil
Plant it in well-drained loam, silt, or sandy soil, since fast drainage counts for more with this tree than anything else. It stays relaxed about pH and grows across a wide 6.0 to 8.0 range. Heavy, soggy ground is the one thing it will not forgive.
Temperature
Key lime sits at the cold-tender end of citrus and thrives in real warmth, comfortable anywhere from 32°F to 100°F (0°C to 38°C) but damaged by frost at the low end. A hard freeze will take it out, so grow it in the ground only where winters stay mild and haul container trees inside before the cold hits.
Humidity
This tree loves the air on the humid side, around 50% to 80%. Outdoors in a warm climate, that sorts itself out. Indoors in dry winter air, cluster it with other plants or set 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 carries micronutrients, and go light rather than heavy. Citrus runs short on minor nutrients, so a feed built for it beats a generic one. Back off as growth slows for the year.
Pruning
Key lime asks for barely any pruning. Cut out dead, damaged, crossing, or low branches and strip any suckers below the graft, since those spring 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. Bump it up when you spot roots circling the pot or bursting through the drainage holes, water running straight through, or growth stalling. Step up just one pot size and refresh the mix rather than drowning it in a giant container.
Size & spacing
Let it run and the tree reaches 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 stretch out, or lean on regular pruning to keep a patio specimen compact.
When to plant
Key lime runs on warmth, not a calendar. Plant it outdoors in spring once frost is well behind you, and only in zones 9 to 11 where winters stay mild. The tree throws its heaviest bloom in spring and delivers green-skinned fruit from summer into fall, and an established tree keeps flowering 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 flags itself right on the leaves, the twigs, or the fruit, and a few of the worst problems are bacterial diseases with no cure. Learn to tell a fungus you can prune away from a quarantine disease you must report, and you stay ahead of the game. Match what you see below, then move before it spreads to the rest of the tree.
Corky raised spots ringed with yellow on leaves and fruit
Scabbed, yellow-ringed spots signal citrus canker, a bacterial disease that roughens the leaves, twigs, and fruit and knocks foliage off the tree. Nothing cures it, so jump on it fast: bag the infected growth, treat with a copper bactericide, and follow your local quarantine and reporting rules. Grab a certified tree and water it at the roots, and you slam the door on this one before it starts.
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 small, lopsided limes flag citrus greening, or HLB, the most serious threat your tree can meet and the disease that has hammered citrus everywhere. The Asian citrus psyllid spreads it, a lab test confirms it, and once a tree has it, no cure exists. Act decisively: pull and destroy the infected tree, drive back the psyllids, and report it to your agricultural authority.
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
Withering tips and browned blossoms usually mean lime anthracnose, also called withertip, a fungus that hits the shoot tips and fresh growth. This one you can knock out at home: prune the affected twigs back to healthy wood and treat with a copper fungicide. Then throw the canopy open for airflow and clear out the deadwood to keep it from creeping 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
A tree that wilts in soggy soil is usually losing its roots to root rot, driven by overwatering or drainage that just cannot keep up. Turn it around fast: cut the water, boost the drainage, and if it is potted, move it into a fresh well-drained mix and snip off the dark, mushy roots. Keep the tree out of standing water for good and it bounces back.
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 to enjoy, but the rest of the tree is off the menu for pets. 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 are heading into the sun.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Mild
A cat that goes after the peel or leaves usually drools, then vomits, with diarrhea and a dull, low mood trailing behind. The oils can leave the skin touchy in sunlight too, so keep the cat shaded for a while.
Dogs Mild
A dog that grabs a bite of foliage or rind tends to land an upset stomach, some drooling, and a flat, listless mood. It mostly stays mild, but the citrus oils can leave skin sensitive to the sun.
Horses Mild
The peel and leaves can hand a horse a sour stomach and a sluggish, off feeling. Horses rarely chase citrus, so trouble stays rare unless prunings land within their reach.
Rabbits Caution
The aromatic oils packed into the rind and foliage upset a rabbit's gut, so keep every part of the tree well clear of the hutch. Any trimmings count as off-limits, not a treat.
Livestock Caution
Goats, sheep, and cattle may pick at fallen leaves or fruit, and the citrus oils can leave them with mild digestive upset. It rarely turns serious, but there is no reason to let them graze the prunings.
Birds Caution
The essential oils loaded into the peel and leaves make the foliage a poor pick around birds. A taste of the flesh worries far less than a beakful of rind or leaf.
People Flesh safe
The flesh and juice are a kitchen staple and safe to eat, so dig in. The catch is the peel oil and sap: handle the fruit or foliage, then step into the sun, and you can raise 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 does not come in many forms, but the handful that exist are worth sorting out before you grab a tree.
Mexican (West Indian) Key lime
This is the classic Key lime that delivers a true Key lime pie, a thorny tree loaded with small 1 to 2 inch fruit that runs very seedy and bursts with aroma.
Thornless Key lime
A nearly spineless selection that fruits much like the original while making the tree a breeze to handle and harvest.
How to propagate
Here is the payoff: Key lime breaks the citrus mold because its seed comes mostly true to type, so you get real choices, from a free seedling to a grafted nursery tree.
SeedEasy
Spring · 3-6 years to first fruit
Seed is the fun, easy route with Key lime, since its seed is largely polyembryonic and comes fairly true to type, unlike most citrus. Sow in spring and hang in there, because a seedling takes 3 to 6 years to hand you its first limes, and they are worth the wait.
GraftingModerate
Spring to summer · 2-3 years to fruit
Budding or grafting onto a rootstock is the nursery's go-to move, since it brings disease resistance and even, reliable vigor. Do it from spring through summer, and a grafted tree races ahead of a seedling, fruiting in about 2 to 3 years.
Stem cuttingsModerate
Spring to summer · 1-2 years
Semi-hardwood cuttings taken in spring or summer will root and set a tree on its own roots within a year or two. It works nicely, though most growers reach for seed or grafting first.
Air layeringModerate
Warm season · 1-2 years
Air-layering through the warm season gives you a tree on its own roots in about 1 to 2 years. It is a solid option for citrus, just slower and fiddlier than starting from seed.
Myths
A Key lime is just a small Persian lime.
Set that idea aside, because these are two different species. The Key lime is Citrus x aurantiifolia, while the Persian or Tahiti lime is Citrus x latifolia, which grows larger, comes seedless, and takes cold better. They look related, but they are not the same fruit.
Citrus is safe for cats and dogs because people eat it.
What flies on your plate flops in a pet's bowl. The ASPCA lists lime as toxic to cats and dogs, because the peel, leaves, and seeds hold essential oils and psoralens that trigger stomach upset and can leave skin sensitive to sunlight. The fruit being edible for you says nothing about it being safe for them.
Key limes grown from seed won't resemble the parent tree.
Most fruit trees roll the dice from seed, but the Key lime beats the odds. Its seed is largely polyembryonic, so the seedlings come fairly true to type and usually match the tree they came from.