Key Lime Tree: Grow Your Own Pie - Epic Gardening

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What’s the first thing you think of when you hear the words “key lime”? Most people picture a pie or a refreshing drink. For us, the key lime tree itself is the real star, and once you learn more about it, you may feel the same way.

The key lime tree is a vigorous tropical plant that produces fruit all year. You will get heavy flushes of citrus in early summer and late fall, followed by a small but steady harvest throughout the rest of the year. The tree also offers lush green foliage and wonderfully fragrant flowers.

And of course, there is the fruit. Key limes are simply smaller versions of regular limes, about the size of a golf ball. They have a thinner peel and a stronger, brighter flavor that more than makes up for their size. Like standard limes, they are usually picked before they are fully ripe. If left on the branch, they will eventually turn yellow.

Key Lime Bush

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Key Lime Tree

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Key Lime Tree

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Quick Care Guide

Scientific Name Citrus aurantifolia ‘Swingle’ Month(s) of Harvest Summer (June through August) Light Full sun Water When the soil starts to dry

Soil Well-draining, nutrient-rich Fertilizer 3-4 times a year, high nitrogen Pests Snow Scale, Citricola Scale, Mites Diseases Citrus canker, Phytophthora, Brown Fruit Spot

All About The Key Lime Tree

The classification of citrus trees has long been debated among taxonomists. The most widely accepted view is that key lime trees are a hybrid of Papeda and citron limes. Native to Southeast Asia, they are believed to have traveled through the Middle East, North Africa, Spain, the West Indies, and eventually to their namesake, the Florida Keys. Today, Citrus aurantifolia is grown commercially in many of these regions, although no longer in Florida.

If you live in the tropics or in zones 9 through 11, this tree will thrive outdoors. For colder climates, dwarf varieties are available for indoor growing, including Citrus aurantifolia ‘Mexican Thornless’.

Key lime trees developed thorns as a defense mechanism against animals and, unintentionally, gardeners. When working with a thorned variety, wear heavy, elbow-length gloves. Dwarf trees and some other cultivars are thornless. Depending on the variety, these trees typically reach six to thirteen feet in height.

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 fall or late winter is usually best. This timing gives the tree a chance to settle into its new home before the active spring growing season. If you are planting in a container that will move between indoors and outdoors, do it at the start of either the warm or cold season so the tree is not relocated while it is still establishing.

Where To Plant

Choose a location that gets about ten hours of full sun each day. The tree also needs protection from cold winds. Planting on the south side of your house helps block northern breezes.

Ideally, key lime trees should be spaced 25 feet apart. At minimum, give yours four to six feet of distance from competing plants. Make sure there is enough space for easy harvesting and pruning.

If you live in an area where winter temperatures stay below 50°F (10°C), bring the tree indoors. Use a container that is only slightly larger than the root ball, since an oversized pot can trap too much moisture. You can size up later as the tree grows.

How To Plant

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

Carefully slide the tree out of its container and brush away any loose soil. Gently massage the rootball so the roots can spread out. Place it in the hole and add the amended backfill. 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, keeping it away from the trunk. This locks in necessary moisture while slowly producing extra nutrients. Replenish the mulch as needed.

Water your newly planted tree frequently until it’s established. You can expect flowers and fruit in two to three years.

How to Grow

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

Light

As we mentioned, Mexican lime trees need about ten hours of full sun. They can tolerate some shade, but they require plenty of light for healthy fruiting. If your plant lives indoors, bring it outside during the summer. When it is inside, keep it by a south-facing window for the best light.

Water

Citrus aurantiifolia can be a bit picky about water, so you’ll need a consistent schedule. Whenever the soil starts to dry out, water the tree deeply. If it is in a container, water until it drains from the holes at the bottom.

Depending on temperature and humidity, you will be watering about one to two times a week. Young key limes need more water than mature ones, so for the first couple of years, water at least twice a week.

Watch closely for signs of over- or underwatering. When overwatered, the leaves turn yellow, and the risk of bacterial or fungal problems increases. Underwatering leads to dry, curled leaves.

Soil

Choose a well-draining soil that leans loamy or sandy (specialty citrus soils work well). The pH should be slightly acidic, between 5.5 and 6.5, and the mix should be rich in nutrients. Work in some compost or animal manure so your tree can feast once it is planted.

When watering, keep an eye on how the soil behaves. It should drain well, without pooling on the surface or staying wet for more than a week.

Temperature and Humidity

Remember that these are tropical plants that need tropical heat. Keep your key lime in temperatures ideally between 60 and 80°F (16 to 27°C). During extreme heat in full sun, give the tree a bit of shade for protection. If temperatures drop below 50°F (10°C), bring your container-grown lime tree indoors.

Keep your tree healthy with high humidity. If you are growing an indoor lime tree, consider using a humidifier to maintain moisture in the air. Keep the tree away from heating ducts, since they dry the air out.

Fertilizing

Since you will be adding organic fertilizer at planting time, you can wait to add supplements until the tree is established and about half a foot larger. After that, apply a granular fertilizer three to four times a year. A balanced fertilizer works well for young, non-bearing trees.

Once they mature, switch to a fertilizer higher in nitrogen and potash. If your key lime tree starts to lose vigor, add a trace mineral supplement with calcium, zinc, iron, and manganese.

Pruning

Prune your key lime at the end of fall or the beginning of spring. This gives the tree plenty of room for new growth during the active season. Whether you are growing a full-size or dwarf key lime tree, proper pruning is essential.

Use clean, sharp clippers and heavy gloves to protect yourself from thorns. Start by removing any dead, dying, or diseased branches. After that, you can reduce the tree’s size, cut back awkwardly shaped branches, and thin the center. Aim for an even shape that promotes good air circulation and future growth. Avoid removing more than one-third of the branches at a time.

Propagation

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

There are two main methods for sprouting key lime seeds. The first is to soak the seeds in warm water and then fold them into a damp paper towel. Place the towel in a sealed plastic bag and tuck it into a warm, dark place like a cupboard. Give the seeds about a week to sprout. Once they do, plant them one quarter inch deep in moist soil in a one-gallon container.

The second method is to plant the seeds one-half inch deep in a small container about four inches deep. Set the container on 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. When the seedlings poke through the soil, remove the heating mat and place the container in some sun. When the seedlings reach a couple of inches tall, transplant them into their permanent home.

No matter which method you use, keep the seedlings in bright sun with evenly moist soil. Protect them from direct heat and frost while they are young. Fertilize every other month until they are well established and actively growing. Seed-grown trees take about five years to begin producing limes.

Air layering is a less common but possible method for propagating Citrus aurantifolia. Make a small cut in a branch, wrap it in peat moss and plastic, and wait for roots to form. Once it has rooted, cut the branch from the tree and plant it in the ground.

Harvesting

Pie makers rejoice! After all that hard work, it’s finally time to harvest your key limes and put them to good use.

Even though ripe limes turn yellow, they’re usually picked while still green. Wait until the fruit becomes a light yellow-green before harvesting. At this stage, it will be about the size of a golf ball and will give slightly when pressed.

Because it isn’t fully ripe, you may need to clip the stem to avoid damaging the branch. Fully yellow limes will drop from the tree on their own and can be gathered from the ground.

Storing

It may be tempting to leave your homegrown limes out on display, but they store much better in the fridge than on the counter. They will last about one to two weeks in the crisper drawer. If you want to stretch their life even further, seal them in a plastic bag before refrigerating. They can last a month or more, which is plenty of time to make a key lime pie.

A cut lime usually lasts five to seven days in the fridge. If you are storing several, check them regularly and discard any that are spoiling or turning moldy so they do not affect the others. Lime juice can be frozen for up to four 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 usually in need of pollinators. For indoor trees or areas with low bee activity, you’ll have to do the pollinating yourself. Lightly swirl a clean paintbrush in the center of a blossom, then transfer the pollen to another flower.

Yellowing leaves typically indicate overwatering or a need for more fertilizer. Check the soil drainage first. If it is sopping wet or puddling on the surface, mix in sand or perlite to improve drainage. Hold off on watering again until the soil begins to dry out. If drainage and watering are not the issue, try adding more fertilizer.

Pests

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

Citricola scale is a serious threat to key limes. It reduces fruit size and overall yield. These small pests suck sap and leave behind honeydew that attracts black sooty mold. The mold interferes with photosynthesis and further reduces fruit production. Insecticides, especially organic petroleum oil sprays, are recommended for control. Biological options such as releasing Metaphycus and Coccophagus predators are also effective.

Citrus mites pose the greatest threat to young trees. In large numbers, they feed on plant juices and cause deformed fruit and a silvery sheen on the leaves. Prevent these mites by removing dead branches, fallen leaves, and other debris. Existing populations can be controlled with a miticide spray or neem oil.

Diseases

If your key lime is constantly in warm, humid weather, it may be susceptible to citrus canker. This disease appears as dark, raised spots that spread across the leaves and branches. Over time, it causes leaf death and fruit drop. Prevent it by keeping the leaves dry while watering. If canker appears, treat the tree with a copper fungicide.

Phytophthora is a soil fungus that can cause gummosis and root rot. Gummosis affects the bark, causing cracks and oozing sap. Root rot leads to decaying roots, yellowing leaves, and stunted growth. Prevent the spread of phytophthora by avoiding overwatering. If you know the soil contains Phytophthora before planting, fumigate it first with metam sodium. Gummosis can be treated by removing infected bark and applying a copper fungicide to the remaining healthy tissue.

Brown fruit rot attacks limes by forming brown spots that quickly spread across the entire fruit, eventually mummifying it. Blossoms can also develop these spots, which causes them to die back and spread the disease to nearby twigs. Brown rot will not kill the tree, but it will significantly reduce fruit yield. If you see these spots, immediately remove the affected fruit or branches and burn or bury them. If the disease persists, apply a copper fungicide.

Frequently Asked Questions

How tall does a key lime tree get?

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.

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

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.

Where do key limes come from?

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