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Why Kumquat Trees Leaves Curl (and How To Fix It)

My parents have a kumquat tree and recently a few of its leaves started to curl. My parents wanted some help to find out why, so, I did some research. Here’s what I found.

Kumquat trees typically get curled leaves due to a lack of water. However, improper nutrients, aphids, extreme weather, and transplant shock can also cause curled leaves. The best way to reduce curled leaves is to provide enough water and removing other stressors.

So, while kumquat trees can get curled leaves from several different issues, how can you identify which issue is causing the curling leaves, and what can we do to fix them?

kumquat tree with some fruit and curled leaves

Under-Watering

Under-watering is the most common reason why kumquat trees get curled leaves. When they don’t have enough water, the leaves curl to retain moisture. If this goes on for long enough, the leaves will dry and turn yellow or brown before falling off.

Kumquat trees are tropic fruit trees, originating from China, so they’re used to warmer, wetter weather and little to no frost. Typically, they grow best in USDA hardiness zones 9-10.

While tropical climates have plenty of humidity and rainfall, growing kumquat trees in drier climates means taking additional steps to make sure they receive the proper watering. For example, my parents live in Ventura, CA where it’s super dry, so they’ll need to care for the tree a bit more than my other family members who live in Florida.

How to Fix

The best way to water kumquat trees is to water only when the soil is dry. You can tell the soil is dry by pushing a finger into the soil, up to the second knuckle. For best results, apply 1 to 2 inches of both compost and mulch to improve water retention and reduce evaporation.

If you live in a drier climate and find that the soil is drying out too fast, there are some things you can do to help.

Compost is an amazing soil amendment since it not only provides sufficient nutrients for kumquat trees but also increases the richness of the soil. For example, with every 1% increase in richness, the soil can hold an additional 20,000 more gallons per acre. Compost can also replace most chemical fertilizers. For best results, use 1 to 2 inches of compost on top of the soil every 1 to 2 months during the growing season.

Mulch is a great cover for soil that drastically reduces evaporation. This makes mulching an extremely helpful practice for kumquat trees in all climates (and especially the drier ones). If the soil is directly exposed, the sun can bake it, while strong wind acts as a blow dryer. When the soil dries, the beneficial bacteria and the tree’s shallow roots begin to die.

Some good mulches to use on kumquat trees are leaves, bark, straw, pine needles, and grass clippings. You can apply 1-2 inches of mulch every 3-6 months on top of the soil.

When applying compost or mulch, spread them evenly under the kumquat tree’s canopy, while keeping them at least 3 inches away from the tree’s trunk. Any closer and they can introduce mold to the tree.

A Lack of Nutrients

Having unbalanced nutrients can cause kumquat trees to develop curled leaves. When a kumquat tree doesn’t have enough nutrients to go around, it will start to shed the less vital parts of the tree that it can’t support. The first parts to be shed are the fruit, blossoms, and leaves, usually in that order.

Sometimes, a lack of nutrients can also cause issues such as yellow leaves and dropping leaves. Other times, the blossoms and fruit can drop too.

How to Fix

To help prevent curled leaves on kumquat trees, use a fertilizer that has twice the nitrogen to phosphorus and potassium, such as an NPK of 6-3-3. Apply 1-2 times per year or use quality compost every 1-2 months during the growing season.

If you’d more information on citrus tree fertilizers, including which ones I recommended, you can check out my recommended fruit tree fertilizer page.

Aphids

aphids on an apple tree leaf

Aphids feed off of the sap from leaves and can cause the leaves to curl on kumquat trees. They’re usually found on the underside of the leaves. You can get rid of aphids by spraying them with water or neem oil, or by releasing ladybugs in your garden. Ladybugs will help since they’re a natural predator to aphids.

Aphids are small insects that appear as small dots underneath leaves. They commonly ranging in colors such as white, yellow, and black.

How to Fix

While they can seem persistent, it’s usually not too difficult to remove them.

For example, I had aphids once on my potted Kaffir lime tree. After looking it up online, I tried spraying them with water from the garden hose. I simply fit my thumb over the nozzle to create more pressure, and it was enough to knock them off the leaves. They haven’t come back since.

Just make sure you’re not using too much pressure to damage the leaves of your kumquat tree.

I’ve also heard great things about using neem oil and ladybugs to remove aphids, I just haven’t needed to use them yet.

Other Stressors

While not as likely as the above reasons, kumquat trees can also get curled leaves from extreme weather, transplant shock, and competition from other plants.

How to Fix

For best results, avoid exposing your kumquat trees to temperatures above or below 20-100ºF. If temperatures exceed this range, potted kumquat trees can be brought indoors while planted kumquat trees can be shaded from the heat or insulated with sheets or cardboard from the cold.

If you’re transplanting or repotting your kumquat tree, ensure that the tree is planted again fairly quickly and that the root ball isn’t damaged. Water generously after transplanting. Sometimes it can take a year for kumquat trees to fully recover and establish a new root system.

Lastly, kumquat trees can grow roots up to 25 feet long. For this reason, when planting, maintain this same distance from other plants and structures such as foundations, fences, and fire hydrants.