Tree · Rutaceae
Key Lime
Citrus × aurantiifolia
Set it in full sun, warmth, and free-draining soil, and this thorny little citrus becomes the sharpest, most aromatic corner of the garden.
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 grown for its tart, deeply fragrant fruit, and it carries a certain sun-warmed glamour with it. It reached the New World through the Caribbean and settled so happily into the Florida Keys that the islands lent it their name. The fruit stays small, only an inch or two across, and holds far more seed and scent than size, which is exactly the character that makes it the lime behind a real Key lime pie.
It is an everbearing tree, so it flowers and fruits across a long season rather than in one brief show, which gives a home a steady rhythm to look forward to. The heaviest bloom arrives in spring, and the green-skinned limes ripen through summer into fall. Left to itself it climbs to 6 to 13 feet (1.8 to 4 m), yet it takes so well to a large pot and to pruning that it settles easily onto a sunny patio, beside a bright bank of windows, or in a glassed-in room where it can anchor the space.
Warmth is what this tree lives for, more than any single detail of its care. It wants heat, abundant sun, and soil that drains fast, and it forgives a short dry spell better than most citrus, which suits a busy household. The real thing to weigh before you commit is disease, since citrus canker and citrus greening have reshaped where and how this tree can be grown at all.
Care
The short version: give it full sun and warmth, soil that drains freely, and steady moisture once the tree has settled into its spot. Feed lightly through the growing season, keep it clear of frost, and prune only to shape it or hold its size.
Light
Key lime lives for full sun, and the brightest spot you can offer is the one where it flowers well and ripens the sweetest fruit. It gets by in partial sun, but the harvest thins and the canopy stretches toward the light. Indoors, the brightest window in the house is its natural home.
Water
Let the top half of the soil dry out between waterings, which lands at roughly every 5 to 10 days depending on the warmth of the room and the size of the pot. The tree handles a short dry spell better than most citrus, yet it carries its fullest crop under steady moisture. Never leave it standing in waterlogged soil.
Soil
Plant it in well-drained loam, silt, or sandy soil, since fast drainage matters to this tree above every other detail. It is relaxed about pH and grows happily across a wide 6.0 to 8.0 range. Heavy, soggy ground is the one condition it will not settle into.
Temperature
Key lime sits at the cold-tender end of citrus and is at its best in real warmth, comfortable anywhere from 32°F to 100°F (0°C to 38°C) but injured by frost at the low end. A hard freeze will finish it, so keep it in the ground only where winters stay mild and bring a container tree indoors before the cold sets in.
Humidity
The tree favors air on the humid side, around 50% to 80%. Outdoors in a warm climate, the setting takes care of that on its own. In dry indoor winter air, group it with other plants or rest it on a pebble tray to lift the moisture around it.
Feeding
Feed through the spring and summer growing season with a balanced citrus fertilizer that carries micronutrients, and go lightly rather than heavily. Citrus is prone to minor-nutrient shortfalls, so a feed made for it serves the tree better than a generic one. Ease off as the season's growth winds down.
Pruning
Key lime asks for little pruning. Clear out dead, damaged, crossing, or low branches and strip any suckers below the graft, since those rise from the rootstock rather than the lime. Beyond that, prune only to hold its size or to shape a container tree to suit its corner.
Repotting
A container Key lime wants 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 one pot size and refresh the mix rather than losing it in an oversized container.
Size & spacing
Given room, 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. Allow an in-ground tree space to fill out its corner, or lean on regular pruning to keep a patio specimen compact and in scale with the setting.
When to plant
Key lime keeps to warmth rather than a calendar, and that shapes where it belongs in a home and garden. Move it outdoors in spring once frost is well behind you, and only in zones 9 to 11 where winters stay gentle. It blooms heaviest in spring and offers 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 shows on the leaves, the twigs, or the fruit, and a couple of the worst problems are bacterial diseases with no cure. It helps to tell a fungus you can prune away from a quarantine disease you must report. Match what you see below, then act before it spreads through the rest of the tree.
Corky raised spots ringed with yellow on leaves and fruit
Scabbed spots wearing a yellow ring are the mark of citrus canker, a bacterial disease that roughens the leaves, twigs, and fruit and thins the tree of its foliage. There is no cure, so the response is a tidy one: bag the infected growth, treat with a copper bactericide, and keep to your local quarantine and reporting rules. A tree bought certified and watered at the roots rather than overhead is the surest way to keep this out of the garden.
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
Mottled leaves and small, lopsided fruit that never colors up are the hallmark of citrus greening, or HLB, the most serious disease a citrus tree can carry and the one that has reshaped the industry. The Asian citrus psyllid spreads it, a lab test confirms it, and there is no cure once a tree is infected. The only responsible course is to remove and destroy the affected tree, keep the psyllids in check, and report it to the 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 newest tips wither and the blossoms brown before they set, the culprit is usually lime anthracnose, a fungus also known as withertip that preys on the tender new growth. It is a manageable one: prune the affected twigs back to healthy wood and treat with a copper fungicide. Keeping the canopy open and the deadwood cleared away is what keeps a well-tended tree free of it.
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 even while its soil stays wet is usually losing its roots to root rot, the result of overwatering or a pot that will not drain. Ease off the water, improve the drainage, and for a container tree, refresh the mix and trim away the dark, mushy roots. The remedy is really a habit: never let the tree stand in water it cannot shed.
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 is not a pet snack, which is worth knowing before it joins the household. 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 has been at the peel or leaves usually drools, then vomits, with some diarrhea and a subdued, low mood to follow. The oils can leave the skin sensitive to sunlight as well, so a shaded corner is the kinder place to recover.
Dogs Mild
A dog that samples the foliage or rind tends toward an upset stomach, a little drooling, and a flat, listless air. It mostly stays mild, though the citrus oils can leave the skin reactive in the sun.
Horses Mild
The peel and leaves can settle a horse with a sour stomach and a dull, off feeling. Horses seldom go seeking citrus, so it is rarely a concern unless prunings are left within reach of the paddock.
Rabbits Caution
The aromatic oils in the rind and foliage sit poorly with a rabbit's delicate digestion, so every part of the tree belongs well away from the hutch. Trimmings are best treated as off-limits rather than a nibble.
Livestock Caution
Goats, sheep, and cattle may pick at fallen leaves or fruit, and the citrus oils can leave them mildly out of sorts. It rarely turns serious, yet there is no call to let them graze the prunings.
Birds Caution
The essential oils that gather in the peel and leaves make the foliage a poor companion for birds. A taste of the flesh is far less of a worry than a beakful of rind or leaf.
People Flesh safe
The flesh and juice are a kitchen mainstay and safe to eat. The catch lies in the peel oil and sap: handle the fruit or foliage and then step into the sun, and a blistering rash called phytophotodermatitis can follow, so a quick wash of the hands comes 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 few that exist are worth telling apart before you choose a tree for the house.
Mexican (West Indian) Key lime
This is the classic Key lime behind a true Key lime pie, a thorny tree carrying small 1 to 2 inch fruit that is richly seedy and deeply aromatic.
Thornless Key lime
A nearly spineless selection that fruits much like the original while making the tree far more pleasant to live with and harvest.
How to propagate
Key lime is unusual among citrus in that its seed comes mostly true to type, which opens up real choices, from a free seedling to a ready-grown grafted nursery tree.
SeedEasy
Spring · 3-6 years to first fruit
Seed is the easy path with Key lime, since its seed is largely polyembryonic and comes fairly true to type, a rarity among citrus. Sow in spring and let patience do its work, as a seedling asks for 3 to 6 years before it offers its first limes.
GraftingModerate
Spring to summer · 2-3 years to fruit
Budding or grafting onto a rootstock is the nursery's preferred route, since it lends disease resistance and an even, dependable vigor. Carried out from spring through summer, a grafted tree comes into fruit 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, setting a tree on its own roots inside a year or two. It works, though most growers turn to seed or grafting first.
Air layeringModerate
Warm season · 1-2 years
Air-layering through the warm season yields an own-rooted tree in about 1 to 2 years. It is a workable option for citrus, only slower and more exacting than starting from seed.
Myths
A Key lime is just a small Persian lime.
The two belong to separate species rather than the same one scaled down. The Key lime is Citrus x aurantiifolia, while the Persian or Tahiti lime is Citrus x latifolia, a larger, seedless fruit that weathers cold more gracefully. A family resemblance does not make them the same fruit.
Citrus is safe for cats and dogs because people eat it.
What belongs on your table does not belong in a pet's bowl. The ASPCA lists lime as toxic to cats and dogs, since the peel, leaves, and seeds carry essential oils and psoralens that unsettle the stomach and can leave skin sensitive to sunlight. A fruit being edible for you says nothing about its safety for them.
Key limes grown from seed won't resemble the parent tree.
Most fruit trees are a gamble from seed, but the Key lime quietly breaks that rule. Its seed is largely polyembryonic, so the seedlings come fairly true to type and tend to echo the tree they came from.