Key Lime Tree: Grow Your Own Pie

What’s the first thing you think of when you hear the words “key lime”? We’re guessing yummy pies jumped into your head or maybe even an alcoholic drink. If you ask us though, we only have eyes for the key lime tree. After we’re done raving about it, this tree is sure to grab your attention as well.

The key lime tree is a vigorous tropical plant that produces all year long. You’ll be flushed with citrus in early summer and late fall and receive a small yet steady harvest for the rest of the year. Not only that, but you’ll be able to enjoy the tree’s lush green growth and fragrant flowers.

And let’s not forget the delicious fruit! Key limes are regular limes in miniature – about the size of a golf ball. They have a thinner peel and stronger flavor than normal limes, which more than makes up for the size. Just like classic limes though, they’re usually picked before they’re ripe. If left on the branch, they’ll eventually turn to yellow limes!

Great Products For Growing Key Limes:

• Monterey Liqui-Cop Liquid Copper Fungicide
• Espoma Citrus-Tone Organic Plant Food
• Espoma Organic Cactus, Palm & Citrus Potting Mix

Quick Care Guide

All About The Key Lime Tree

The classification of citrus trees has long been debated among taxonomists. The most popular belief is that the key lime trees are a hybrid of the Papeda and Citron limes. It’s native to Southeast Asia and believed to have voyaged through the Middle East, North Africa, Spain, West Indies, and finally, its namesake, the Florida Keys (a small chain of islands off Florida). Currently, the Citrus aurantifolia is grown commercially in many of these areas, except Florida.

If you live in the tropics or zones 9-11, you’re in luck – this tree will thrive outdoors. For you northerners, dwarf trees are available for indoor growing (look for Citrus aurantifolia ‘Mexican Thornless’).

Key lime trees evolved thorns as a defense mechanism against animals – and gardeners apparently. When working with this plant, be sure to wear heavy, elbow-length gloves. As mentioned, the dwarf tree is thornless, as well as other cultivars. These trees will take up 6-13 feet of vertical space.

Planting Key Limes

To make a key lime pie from scratch you must first plant a tree. Here’s what you need to know to plant your future pie!

When To Plant

You can plant your tree at any time of year, but we recommend late winter. This gives the tree time to settle into its new home before the busy growing season in spring. If you’re planting in an indoor/outdoor container, do so at the beginning of the warm or cold season so it doesn’t have to move locations while still getting settled. Air Pots are great for helping trees establish a healthy root ball.

Where To Plant

Choose a location that gets around 10 hours of full sun each day. It also needs to be protected from cold winds; Planting it on the south side of your house will block out the northern breeze.

Ideally, these trees should be set 25 feet apart. At the very least though, place yours 4-6 feet away from competitors. Leave space for easy harvesting and pruning.

Bring the tree inside if you live in an area that’s consistently below 50* F in the winter. Use a container that’s slightly larger than the rootball (you may need to size up later). Don’t use one too large or it’ll trap too much moisture.

How To Plant

Whether you bought a baby tree or have grown one from seed, this is how we recommend you plant it. Start by digging a hole as deep as the rootball and twice as wide. Mix some organic compost into the backfill as your tree will be hungry!

Carefully slide the tree out of its container and brush away loose soil. Gently massage the rootball so the roots can spread out. Now, just stick it in the hole and add the doctored backfill soil. Lightly pat down the soil to collapse any air pockets.

Lastly, and most importantly, add your choice of mulch to the surface. Spread a couple of inches all around the tree, avoiding the trunk. This will lock in the necessary moisture while producing extra nutrients. Replenish the mulch as needed over time.

Water your newly planted tree frequently until it’s established. You can expect flowers and fruit in 2-3 years.

Key Lime Tree Care

Now that the hard part’s out of the way, it’s all low maintenance and fertilizer until harvest. Here’s what you need to know.

Sun and Temperature

As we mentioned, Mexican lime trees need 10 hours of full sun. They may tolerate some shade, but need lots of light for healthy fruiting. If your plant lives indoors, bring it out during the summer. When inside, keep it by a south-facing window for optimal light.

Remember that these are tropical plants that need tropical heat. Keep your plant in temperatures ideally between 60-80° F. In cases of extreme heat in full sun, give your tree some shade to protect it. If the temperature drops below 50° F, bring your container lime tree indoor.

Water & Humidity

Citrus aurantiifolia can be a bit picky about their water, so you’ll need a consistent schedule. Whenever the soil starts to dry out, water them deeply. If it’s in a container, do so until the water leaks out the drainage holes. Depending on the temperature and humidity, you’ll be watering about 1-2 times a week. Young key limes need more water than mature ones. For the first 1-2 years of its life, you need to water your tree at least twice a week.

Diligently watch for signs of over and underwatering. When overwatered, the leaves will turn yellow and the risk for bacterial and fungal growth grows. Underwatering results in dry, curled leaves.

Keep your tree spry with high humidity. If you’re growing an indoor lime tree, you may want to use a humidifier to keep it happy. Keep the tree away from heating ducts since they dry out the air.

Soil

Choose a well-draining soil that’s on the loamy or sandy side (search for specialty citrus tree soils). The pH level needs to be slightly acidic (5.5-6.5) and have an abundance of nutrients. Work in some compost or animal manure so your tree can feast once it’s planted.

When watering, watch the soil to make sure it drains well enough. It shouldn’t be pooling water on the top or taking more than a week to dry out.

Fertilizing

Since you’ll be adding organic fertilizer when the tree is planted, you can hold off on supplements until it’s established and half a foot larger. Then, apply a granular fertilizer 3-4 times throughout the year. A balanced fertilizer is fine for young, non-bearing trees. When they’ve matured though, use a fertilizer that’s high in nitrogen and potash. If your key lime tree has lost its vigor, try adding a trace mineral supplement with calcium, zinc, iron, and manganese.

Pruning

Prune your key lime at the end of fall or beginning of spring. This allows plenty of room for new growth during the growing season. Whether you’re growing a full size or dwarf key lime tree, it’ll need to be pruned properly.

When pruning, always use clean, sharp clippers and heavy gloves to protect from thorns. To begin, search for and remove any dead, dying, or diseased branches. From there, you can trim down the size, cut back awkwardly-shaped branches, and thin the center. Aim for an even shape that allows for good air circulation and future growth. However, don’t remove more than a third of the branches at a time.

Propagation

Even though it’s a hybrid, key lime trees grow well from seed. What’s better, you can start them any time of year. Take the seeds from a fresh, healthy lime or order some from a trusted seed nursery. 

There are two main methods of sprouting key lime seeds. The first is to soak them in warm water and then fold them in a damp paper towel. Put the towel in a sealed plastic bag and place it in a warm, dark place like a cupboard. Give the seeds about a week to sprout. Then, you can plant them ¼ inch deep in moist soil in a one-gallon container.

The second method is to plant the seeds ½” deep in a small container (about 4 inches deep). Place the container on top of a heating mat and cover it with a clear cover, such as plastic wrap with a few holes punched in it. Mist the soil with a spray bottle daily. Remove the heating mat when the seedlings poke out of the soil and place them in some sun. When they’re a couple of inches tall, transplant them into their permanent home.

No matter the method, you can now keep the seedlings in the sun with moist soil. It’s crucial to protect them from direct heat and frost while they’re young. Fertilize them every other month until they’re well established and actively growing. It’ll take around 5 years for the seedlings to turn into lime producers.

Air layering is a less common, but possible, method for key lime trees. It involves making a cut in a branch and wrapping it in peat moss and plastic. In time, the cut will sprout roots that feed on the peat moss. The branch is then cut from the tree and planted in the ground. For more detailed instructions on air layering, refer to this article.

Harvesting and Storing Key Limes

Pie makers rejoice! After all that hard work, it’s time to harvest the key lime and put it to good use.

Harvesting

Even though limes are yellow when they’re fully ripe, they’re usually picked green. Wait until the fruit turns light yellow-green before picking it by hand. The lime will be the size of a golf ball and give slightly when pressed. Because it’s not fully ripe, you may have to clip the stem so as not to damage the branch. A yellow lime will fall off the tree and should be gathered from the ground.

Storing

It may be tempting to put your home-grown limes on display, but they store better in the fridge than on the counter. They’ll last for about 1-2 weeks in the crisper drawer of the fridge. If you really want to stretch their life though, seal them in a plastic bag before refrigerating. They can last a month or more – that’s plenty of time to make a key lime pie!

A cut lime usually lasts 5-7 days in the fridge. When storing multiples, search for and immediately discard ones that are spoiling or moldy so they don’t contaminate the others. Lime juice can be frozen for up to 4 months.

Troubleshooting

As a good gardener, you should always be in search of growing problems, pests, and diseases. Catching them early can be an issue of life and death.

Growing Problems

Trees that produce healthy flowers but no fruit are most likely in need of pollinators. For indoor trees and areas with small bee populations, you’ll have to get the job done yourself. Simply swirl a clean paintbrush in the center of a blossom and transfer the pollen to another flower.

Yellowing leaves are usually a sign that the key lime is overwatered or needs more fertilizer. Check the soil drainage first. If it’s sopping wet or collecting puddles, you need to mix in some sand or perlite. Hold off on watering again until the soil starts to dry out. If the soil and water levels are fine, try adding more fertilizer.

Pests

Citrus snow scale, also called white louse, is an aphid-like insect that damages the trunk and branches. In large numbers, they make the tree look like it’s dusted with snow. Parasitic wasps such as Aphytis lingnanensis and Aphytis gordonae are commonly introduced to control the snow scale population. Horticultural oils will also eliminate these pests.

A serious threat to key limes, Citricola scale reduces fruit size and overall yield. These small pests suck out the juice and leave behind honeydew that attracts black sooty mold. The mold then inhibits photosynthesis, resulting in damage to fruit production. Insecticide is the top recommendation for handling these pests, specifically organic petroleum oil spray. Biological controls are also effective by introducing predators like Metaphycus and Coccophagus.

Citrus mites pose the worst threat to young trees. In large numbers, they search for juice and cause deformed fruit and a silvery coloring on the leaves. Prevent these mites by removing dead branches, leaves, and other debris. Existing populations can be controlled with miticide spray or neem oil.

Diseases

If your key lime is constantly in warm, humid weather, it may be susceptible to citrus canker. This fungal growth appears in dark spots that spread across the leaves and branches. Eventually, it’ll cause leaf death and fruit drop. Prevent this by keeping the leaves dry while watering them. To stop the disease, apply a copper fungicide.

Phytophthora is a soil fungus that can cause gummosis and/or root rot. Gummosis invades the bark, causing it to crack and ooze. Root rot results in decaying roots, yellowing leaves, and stunted growth. To prevent the fungus from spreading, don’t overwater. If you know there’s phytophthora in the soil before planting, fumigate it first with metam sodium. Gummosis can be cured by removing infected bark and treating the rest with copper fungicide.

Brown fruit rot will attack your precious limes with brown spots. From there, the spots will consume the whole fruit and mummify it. The blossoms can also be hit with these spots, causing them to die back and spread the disease to the surrounding twigs. Brown rot won’t kill the key lime trees, but will drastically reduce the fruit yield. If you see these spots, immediately remove the affected areas and burn or bury them. If the disease persists, apply a copper fungicide.

Frequently Asked Questions

Q: How tall does a key lime tree get?

A: Key lime trees are about 6-13 feet tall. If that’s too tall for you, there are dwarf varieties that only reach 2-6 feet tall. Search for these varieties at a nursery.

Q: What is the difference between a lime and a key lime?

A: Key limes are much smaller, have a thinner peel, and are more acidic. They have a stronger flavor than regular limes, which is why they’re commonly used in recipes and drinks.

Q: Where do key limes come from?

A: Key limes are originally from southeast Asia. They’ve traveled around the world to come to the Florida Keys, their namesake.