Tree · Rutaceae
Key Lime
Citrus × aurantiifolia
Give this thorny little citrus full sun, warmth, and free-draining soil, and it happily pays you back with 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 it is grown for one wonderful reason: its tart, deeply fragrant fruit. It traveled to the New World through the Caribbean and settled so contentedly into the Florida Keys that the islands lent it their name. Each lime stays small, only an inch or two across, yet it is brimming with seeds and scent, which is exactly what makes it the fruit behind a real Key lime pie.
This is an everbearing tree, so it flowers and fruits over a long, generous stretch instead of all at once, which takes a lot of pressure off you as a grower. The main flush of bloom arrives in spring, and the limes ripen through summer into fall, picked while their skin is still green. Given its head the tree grows 6 to 13 feet (1.8 to 4 m) tall, but it takes kindly to a pot and to pruning, so you can easily keep it much smaller on a patio or in a bright room.
If there is one thing to be mindful of, it is cold, because the Key lime minds a chill far more than anything else. It simply wants heat, sun, and fast-draining soil, and it forgives a short dry spell better than most citrus. The bigger thing to keep an eye on is disease, since citrus canker and citrus greening have changed where and how this tree can be grown.
Care
The short version: give it full sun and warmth, soil that drains freely, and steady moisture once it has settled in. Feed it lightly through the growing season, spare it any frost, and prune only to shape it or hold its size, and you will do just fine.
Light
Key lime loves full sun, and the more it gets, the better it flowers and the sweeter the fruit ripens. It will get by in partial sun, though the harvest thins and the canopy stretches when it is shaded, so do not worry if a spot is not perfect. Indoors, simply give it 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. This tree copes with a short drought better than most citrus, yet it sets its heaviest crop with steady moisture. The one rule to hold to is never leaving it standing in waterlogged soil.
Soil
Plant it in well-drained loam, silt, or sandy soil, because fast drainage matters to this tree more than almost anything else. Happily, it is easygoing about pH and grows across a wide 6.0 to 8.0 range. Heavy, soggy ground is really the only thing it will not forgive.
Temperature
Key lime sits at the cold-tender end of citrus and is happiest in genuine warmth, comfortable anywhere from 32°F to 100°F (0°C to 38°C) but harmed by frost at the low end. A hard freeze can take it, so grow it in the ground only where winters stay mild, and bring container trees inside before the cold sets in.
Humidity
This tree prefers the air on the humid side, around 50% to 80%. Outdoors in a warm climate, that simply happens on its own. Indoors in dry winter air, group it with other plants or set it on a pebble tray to lift the moisture around it, and it will thank you.
Feeding
Feed it through the spring and summer growing season with a balanced citrus fertilizer that includes micronutrients, going lightly rather than heavily. Citrus is prone to minor-nutrient shortages, so a feed made just for it beats a generic one. Ease off as the year's growth slows, and let the tree rest.
Pruning
Key lime asks very little of you here. Take out any dead, damaged, crossing, or low branches and strip off suckers below the graft, since those come from the rootstock rather than the lime. Beyond that, prune only to hold its size or shape it as a container tree, and you can leave the rest be.
Repotting
A container Key lime appreciates a fresh pot every 2 to 3 years. Step it up when you notice roots circling the pot or slipping through the drainage holes, water running straight through, or growth stalling. Move up just one pot size and refresh the mix rather than overwhelming it in a giant container.
Size & spacing
Left to grow, 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 fill out, or lean gently on regular pruning to keep a patio specimen compact and easy to manage.
When to plant
Key lime follows warmth rather than a calendar, which makes the timing forgiving. Set it outdoors in spring once frost is well behind you, and only in zones 9 to 11 where winters stay gentle. The tree blooms heaviest in spring and offers up green-skinned fruit from summer into fall, and an established tree will 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 where you can see it, on the leaves, twigs, or fruit, and only a couple of the worst problems are bacterial diseases with no cure. Learning to tell a fungus you can simply prune away from a quarantine disease you must report is half the battle. Match what you are seeing below, then act early, and you will usually stay ahead of it.
Corky raised spots ringed with yellow on leaves and fruit
If you spot those scabby, yellow-ringed spots, you are likely looking at citrus canker, a bacterial disease that roughens the leaves, twigs, and fruit and drops leaves from the tree. Take heart that the response is straightforward even without a cure: bag the sick growth, treat with a copper bactericide, and follow your local quarantine and reporting rules. Starting with certified trees and keeping water off the leaves gives you the best protection going forward.
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 little lopsided limes point to citrus greening, or HLB, the most serious disease your tree can face and the one that has hit citrus hardest. An insect called the Asian citrus psyllid carries it, a lab test confirms it, and sadly there is no cure once a tree is infected. The kind thing to do for your other trees is to remove and destroy the sick one, keep the psyllids in check, 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
When the fresh tips wither and the flowers brown, that is usually lime anthracnose, also called withertip, a fungus that takes out shoot tips and young growth. You can handle this one at home: prune the affected twigs back to healthy wood and treat with a copper fungicide. Opening up the canopy for better airflow and clearing away deadwood keeps it from settling back in.
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 droops while the soil is still wet is most often losing its roots to root rot from too much water or poor drainage. The good news is that it is very recoverable: ease back on the watering, help the soil drain, and if it lives in a pot, move it into a fresh well-drained mix and snip away the dark, mushy roots. All it really takes is making sure the tree never sits in standing water again.
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 not a pet snack, so it is worth a gentle heads-up. 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
Should a cat chew on the peel or leaves, you will likely see drooling followed by vomiting, some diarrhea, and a quiet, dull mood. The oils can also leave its skin touchy in sunlight, so a shady rest helps.
Dogs Mild
A dog that nibbles the foliage or rind tends to get an upset stomach, drool a bit, and act flat and listless for a while. Most of the time it stays mild, though the citrus oils can make skin sensitive to the sun.
Horses Mild
The peel and leaves can leave a horse with a sour stomach and a sluggish, off feeling. Happily, horses rarely go looking for citrus, so trouble is uncommon unless prunings land within their reach.
Rabbits Caution
A rabbit's gut simply doesn't take to the aromatic oils in the rind and foliage, so it is kindest to keep every part of the tree out of the hutch. Treat any trimmings as off-limits rather than a snack.
Livestock Caution
Goats, sheep, and cattle may nose at fallen leaves or fruit, and the citrus oils can leave them with a bit of mild digestive upset. It is seldom serious, but there is no need to let them graze the prunings.
Birds Caution
With essential oils concentrated in the peel and leaves, the foliage makes a poor companion for birds. A taste of the flesh is far gentler than a beakful of rind or leaf, so keep the trimmings well away.
People Flesh safe
You can relax about the flesh and juice, which are a kitchen staple and safe to eat. The one thing to watch is the peel oil and sap: handle the fruit or foliage and then head into the sun, and you can end up with a blistering rash called phytophotodermatitis, so a quick hand wash first keeps you clear.
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 knowing before you bring a tree home.
Mexican (West Indian) Key lime
This is the true Key lime you want for a real Key lime pie, a thorny tree hung with small 1 to 2 inch fruit that comes very seedy and richly aromatic.
Thornless Key lime
If the spines put you off, this nearly spineless selection fruits much like the original while being far gentler to handle and pick.
How to propagate
Here is something reassuring: Key lime is unusual among citrus in that its seed comes mostly true to type, so you have real choices, from a free seedling to a ready grafted nursery tree.
SeedEasy
Spring · 3-6 years to first fruit
Seed is the friendly, easy route with Key lime, because its seed is largely polyembryonic and comes fairly true to type, unlike most citrus. Sow in spring and settle in for the wait, since a seedling takes 3 to 6 years before it hands you those first limes.
GraftingModerate
Spring to summer · 2-3 years to fruit
Budding or grafting onto a rootstock is the nursery's go-to, since it brings disease resistance and steady, reliable vigor. Done from spring through summer, a grafted tree rewards you sooner than a seedling, in roughly 2 to 3 years.
Stem cuttingsModerate
Spring to summer · 1-2 years
Semi-hardwood cuttings taken in spring or summer will happily root, putting a tree on its own roots within a year or two. It works well enough, 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 perfectly workable option for citrus, just a bit slower and fiddlier than starting from seed.
Myths
A Key lime is just a small Persian lime.
These are two separate species, so you can set that idea aside. The Key lime is Citrus x aurantiifolia, while the Persian or Tahiti lime is Citrus x latifolia, a larger, seedless fruit that takes cold in better stride. They may look like cousins, but they are not the same fruit.
Citrus is safe for cats and dogs because people eat it.
What is happily fine on your plate is not fine 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 bring on stomach upset and can leave skin sensitive to sunlight. A fruit being edible for you tells you nothing about whether it is safe for them.
Key limes grown from seed won't resemble the parent tree.
Most fruit trees are a roll of the dice from seed, but the Key lime is a happy exception. Its seed is largely polyembryonic, so the seedlings come fairly true to type and usually turn out much like the tree they came from.