Key Lime vs Lime, Citrus Soil, and Potted Citrus

By David S., Green Thumb Nursery

Quick answer: A key lime, also called a Mexican lime, is a smaller, seedier, and more aromatic lime than the Persian limes sold in grocery stores, and in California its main crop ripens from October to December (UC Riverside). Citrus season is also planting season: in mild Southern California, citrus can go in the ground almost any time of year. In the ground or in a pot, success comes down to sun, well drained soil, and steady feeding. In pots, use a fast draining citrus mix rather than garden soil, and plan on repotting about every three years in spring.

Meyer lemon, Eureka lemon, and Mexican lime (the key lime) are each part of the large variety of citrus that Green Thumb Nursery offers, along with Bearss lime (the seedless Persian lime you see at the grocery store), Tango mandarin in dwarf and standard sizes, blood orange, and Gold Nugget tangerine. All of them bear reliably in Southern California, dwarf forms double as a productive screen or windbreak, and citrus season is a wonderful time to plant them.

What Is a Key Lime?

A key lime is the small, round, wonderfully fragrant lime properly known as Citrus aurantifolia, also written Citrus x aurantiifolia. Depending on where you shop, you will also hear it called a Mexican lime, a West Indian lime, or a bartender’s lime; they are all the same fruit (UC Riverside Citrus Variety Collection). The fruit is only about an inch and a half across, is usually picked green, and carries far more aroma than its size suggests. The tree itself stays on the small side, often with thorns, and it is the classic lime for pies, marinades, and drinks.

Key Lime vs Regular Lime: What Is the Difference?

The difference between a key lime and a regular lime comes down to size, seeds, flavor, and cold hardiness. The regular lime at the grocery store is the Persian lime, also sold as Bearss or Tahiti lime, and it accounts for roughly 90 percent of fresh limes sold in the United States (UF/IFAS). Key limes are smaller and moderately seedy with a stronger, more distinctive flavor, while Persian limes are larger, seedless, and milder. The trees differ too: key lime trees are often thorny and are the most cold sensitive citrus we sell, while Persian lime trees are nearly thornless, vigorous, and noticeably hardier (UC Riverside).

Trait	Key lime (Mexican lime)	Persian lime (Bearss or Tahiti)
Botanical name	Citrus aurantifolia	Citrus latifolia
Fruit	About 1.5 inches, round, moderately seedy	2 to 2.5 inches, seedless
Flavor	Intense and aromatic, the classic pie lime	Milder, the everyday grocery store lime
Tree	Smaller, often thorny	Vigorous, nearly thornless
Cold hardiness	Most cold sensitive citrus; foliage damage can start at 30 to 32 degrees F	Hardier; does well wherever lemons grow

When Are Key Limes in Season?

Key limes are in season from October to December in California, when the main crop ripens, which is one of the reasons we call fall the start of citrus season (UC Riverside). Because the trees are everbearing in warm climates, you may also see some fruit in almost any month (UF/IFAS). Other citrus follow right behind through the winter: mandarins, navel oranges, and blood oranges all peak in the cooler months. Plan it well and a small home orchard can hand you fresh fruit nearly year round; our guide to growing twelve months of fruit shows how the seasons stack up.

What Kind of Soil Do Citrus Trees Need?

The real secret to successfully growing citrus is all in the soil. Citrus trees prefer slightly acidic soil, with a pH of about 6.0 to 6.5 being ideal (Clemson Cooperative Extension), though most citrus grow well in anything from 6 to 8 (Texas A&M AgriLife Extension). An excellent tip for growing beautiful citrus trees is to start with a soil pH test and then amend as needed. This is true whether you are growing trees in the ground or in a decorative pot.

Drainage matters even more than pH. Citrus roots cannot sit in soggy ground; prolonged waterlogging invites Phytophthora root and crown rot, a common killer of overwatered home citrus trees. Plant on a slight mound if your soil is heavy, and let the soil dry down between deep waterings (UC IPM).

Feeding Citrus: Before You Plant and After

Soil for citrus is divided into two concerns: preparing the ground before you plant, and the ongoing care after. Before you plant citrus, amend the soil. A good product, and one our staff recommend often, is Down to Earth Bio-Live 5-4-2 fertilizer, an organic blend with bumped up nitrogen and phosphate. It is also a bio-live product, which means it is full of beneficial soil organisms, and these little creatures improve the soil structure so the tree has better access to nutrients and water. Another option is E.B. Stone Citrus and Palm Soil, an organic blend of fir bark, lava rock, and sphagnum moss that improves aeration and water retention; it is best used with a citrus fertilizer.

Once the tree is established, switch to an ongoing feed such as Down to Earth Citrus Mix 6-3-3, which bumps up the nitrogen to help the tree expand its canopy while building blooms and fruit. Citrus are hungry trees, especially for nitrogen: UC Master Gardeners suggest up to about 1 pound of actual nitrogen per year for a full size mature tree, split into two or three applications between late winter and early summer (UC Master Gardeners). Happy trees grow best in soil that is prepared for them and then fed as they grow.

Best Soil for Citrus Trees in Pots

Growing citrus in a container is one of the easiest ways to enjoy it in Southern California, and it is the smart play for cold sensitive trees like key limes, since a potted tree can be moved to a warm, protected spot on frosty nights. Start with the right mix: use a commercial potting mix labeled for citrus or cactus that drains quickly, never straight garden soil, which compacts in a pot and starves roots of air (University of Maryland Extension). If you prefer a DIY citrus potting mix, University of Minnesota Extension suggests about one third sterile potting soil, one third perlite or vermiculite, and one third peat or similar organic matter (UMN Extension). E.B. Stone Citrus and Palm Soil is our ready made version of that fast draining idea.

Give the roots room: a 15 gallon container or half barrel suits most varieties (UC Master Gardeners), and choose a tree on dwarf rootstock, which is what keeps a potted citrus happy for years. Our rootstock guide explains why the roots make the tree. Water when the top 2 to 3 inches of mix feel dry; a finger test once or twice a week is the simplest schedule, and remember that pots dry out faster than garden beds (UMD Extension).

When to Repot a Lemon Tree

Plan on repotting a container lemon or lime about every three years, and do it in spring, when the tree is ready to push new growth (UMD Extension; University of Georgia Extension). The tree will tell you when it is time:

Roots circling the inside of the pot or poking out of the drainage holes
Soil that seems to dry out faster and faster
Growth that has clearly slowed

When those signs show up, the repotting routine is simple:

Choose a pot just 3 to 4 inches wider than the current one.
Set the tree at the same depth it was growing before.
Refresh with new citrus mix rather than reusing tired soil.

Keeping Citrus Pests in Check

The citrus pest we hear about most is the citrus leafminer, a tiny moth whose larvae tunnel through tender new leaves and leave squiggly silver trails. Like other garden plants, citrus trees have their share of pest issues, and the key with pest control is to prevent an infestation before it becomes an epidemic. The good news: mature trees can tolerate the damage with little effect on growth or fruit, so on an established tree the best treatment is usually none at all (UC IPM). You can see exactly what the damage looks like in our citrus leafminer identification guide, and find out when treatment makes sense in our citrus leafminer treatment guide.

For young trees that need help, Captain Jack’s Deadbug Brew is our go-to organic option. Its active ingredient, spinosad, is an insecticide derived from the fermentation products of a natural soil bacterium, Saccharopolyspora spinosa (National Pesticide Information Center). Spray the tender new flush of leaves where the larvae feed rather than drenching the whole tree. One important caution: spinosad is highly toxic to bees while the spray is wet, so apply it in the evening after bees have finished foraging; once it dries, the risk to bees is considered negligible. And skip systemic insecticides around bloom entirely: systemics move through the tree into nectar and pollen, where they can put bees at risk (UC IPM). Our garden experts can point you to the right product for your tree and the time of year.

Is Now a Good Time to Plant Citrus?

Yes. In mild Southern California, citrus from containers can be planted almost any time of year, with the classic recommendation being right after the last frost in spring (UC IPM). Key limes are rated for USDA zones 9a through 11b (NC State Extension), and most citrus do well across the same zone 9 to 11 range that covers most of Southern California. Fall planting works well here too, and it puts a tree in your yard just as the market fills with fruit, a nice reminder of what you are growing toward. We are fond of the phrase, grow what you eat, and adding citrus to your yard is a fantastic way to add homegrown fruit to your diet. For how to pick a healthy tree and why the weeks before peak season are the smart time to shop, see our guide to buying your citrus before the season gets away.

Frequently Asked Questions

Is a key lime the same as a Mexican lime?

Yes. Key lime, Mexican lime, West Indian lime, and bartender’s lime are all common names for the same small, aromatic citrus, Citrus aurantifolia. The name you see usually depends on where the fruit was grown or sold.

Where does key lime pie come from?

Key lime pie comes from the Florida Keys, where this little lime naturalized and gave both the fruit and the dessert their name. Florida designated it the official state pie in 2006 (Florida Statutes). The traditional filling uses key lime juice, which is sharper and more aromatic than juice from grocery store limes.

Are key limes harder to grow than regular limes?

They are a little more demanding, mainly because key limes are the most cold sensitive citrus: foliage damage can begin at 30 to 32 degrees F (UF/IFAS). Persian limes take a few more degrees of cold and do well wherever lemons grow. Near the coast key limes are easy; in colder inland pockets, grow one in a pot you can move, or be ready to cover it on frosty nights.

Can you grow a key lime tree in a pot?

Yes, a key lime on dwarf rootstock is one of the best citrus trees for a container. Use a fast draining citrus mix in a 15 gallon pot or half barrel, give it your sunniest spot, and move it somewhere protected when frost threatens.

How often should you water a citrus tree in a pot?

Water a potted citrus when the top 2 to 3 inches of mix feel dry, which usually means checking with a finger once or twice a week. Pots dry out faster than garden soil, so expect to water more often during hot or windy weather.

When is the best time to plant citrus trees in Southern California?

Spring, right after the last frost, is the classic time, but in our mild climate citrus from containers can be planted almost year round, including fall. Our citrus buying guide covers how to pick a healthy tree before the seasonal rush.

Where can you buy a key lime tree?

All five Green Thumb Nursery locations across Southern California carry key lime trees along with dozens of other citrus varieties. Availability changes daily by store, so if you are after a particular tree, call ahead or stop by your nearest Green Thumb Nursery and we will point you to what is in stock.

Sources

Remember that citrus trees are very popular, and as such, plants, trees, and beneficial insects are in demand products whose availability changes daily for each of our five store locations throughout Southern California. If you are interested in a particular plant, citrus tree, or product featured in our garden newsletter, it is always best to call ahead and check if it is available.

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