My parents have a kumquat tree and it’s starting to lose leaves, so they asked if I knew how to treat it. I had an idea, but I wanted to dig a bit deeper, so I did some more research. Here’s what I found.

Kumquat trees generally lose their leaves from under-watering, over-watering, and extreme climates. However, transplant shock, pests, and diseases can also cause leaves to drop. For best results, only water the tree when the soil is dry, provide compost and mulch, and keep the tree between 10ºF to 100ºF.

So, while kumquat tree leaves fall off for several reasons, how can we tell which issue is causing it, and how can we fix it? Let’s take a closer look.

a potted kumquat tree with lots of fruit

Over or Under-Watering

Over and under-watering kumquat trees are the most likely cause of dropping leaves. Ideally, kumquat trees prefer moist soil, similar to a wrung-out sponge, and the best rule when watering is to only water when the soil is dry. You can determine this by pushing a finger into the top 2-4 inches of soil.

A common symptom of under-watering kumquat trees is when the tree’s leaves start to curl.

Since there are many factors to the amount and frequency you have to water (such as humidity, sunlight, wind, and tree size), there’s no one golden rule with how much to water and how often. However, checking the soil before watering is the best way to prevent over and under-watering.

To check if the kumquat tree needs to be watered, push a finger in to the first 2-4 inches of soil. If it’s dry, water it. If it’s wet, hold off on watering.

Soil that is too wet for too long can cause issues such a root rot, which eventually kills the kumquat tree. This most often occurs when the soil’s drainage is poor (common in heavy clay soils).

However, once the kumquat tree’s soil is well-draining, there are some practices you can use which help retain the water in the soil and help the tree become more water independent.

Compost (other than providing valuable nutrients) significantly increases the soil’s richness and water retention. So much so, that every 1% increase in the soil’s organic matter holds an additional 20,000 gallons of water per acre (source).

Compost also feeds beneficial soil life such as earthworms and mycorrhizal fungi—which provide even more nutrients, water retention, as well as disease resistance for the tree.

Mycorrhizal fungi promote many aspects of plant life, in particular improved nutrition, better growth, stress tolerance, and disease resistance.

Department of Biology, University of Fribourg, Switzerland

Mulching protects the soil and beneficial soil life from drying out in the sun and wind. It also greatly retains water by capturing condensation, or dew, from the ground. Also, in cold weather, mulch provides a layer of insulation for the tree and its roots. Some good mulches for kumquat trees are leaves, bark, pine needles, and straw.

So, how much compost and mulch should you use on your kumquat tree?

Apply 2 inches of compost every 1-2 months and 2-6 inches of mulch every 3-6 months. Keep these materials under the drip line of the tree, and at least 3 inches from the trunk to prevent mold.

By checking the soil with the finger test, providing good drainage, and only watering when the soil is dry, you’ll provide your kumquat tree with the right amount of water at the right time.

If you need to adjust your soil’s drainage, planted kumquat trees will benefit when compost and mulch break down into smaller particles over time. This is naturally worked into the soil. On the other hand, if you have a potted kumquat tree with poor drainage, the best solution is repotting it with fresh potting soil.

Extreme Temperatures

Cold-Hardy Citrus Tree VarietiesNon Cold-Hardy Citrus Tree Varieties
Trifoliate OrangeGrapefruit
Sour OrangeCitron
Sweet Orange
Source: L.K. Jackson and T.R. Fasulo, University of Florida Cooperative Extension Service

If temperatures get too hot or cold, kumquat trees will get stressed and begin to drop their leaves. Kumquat trees can survive temperatures as hot as 100ºF, and as cold as 10ºF when dormant. If the kumquat tree is grown on a trifoliate orange rootstock, it can typically survive even colder temperatures.

For best results, most citrus trees (including kumquats) should be grown in USDA hardiness zones 9-11. Since citrus trees are originally from the tropics, growing them in the subtropics or tropics will give them the best chance of growth and fruiting.

However, if you’re trying to grow kumquat trees in other zones, or have an unusually hot or cold spell, there are some tips you can try to help the tree survive.

Cold Weather Tips

  • Insulate the tree’s canopy with bedsheets or its trunk with cardboard. Provide windbreaks if possible.
  • Plant kumquat trees facing the south to get the maximum amount of sunlight and warmth. Planting along southern facing walls also helps.
  • Apply mulch to help insulate the roots.

Hot Weather Tips

  • Provide compost and mulch to prevent the soil from drying out and baking in the sun.
  • Check the soil’s moisture often, especially on hot days. Water when it’s dry.
  • If possible, shade the tree when temperatures exceed 100ºF or if you notice scorched leaves.

Keep in mind that moving kumquat trees indoors can lead to more falling leaves. This is either due to a sudden temperature swing (of 20ºF or more), or the central heat is drying out the leaves.

Last winter, after I moved my Meyer lemon tree inside, the central heat started stressing it and causing its leaves to drop. I then moved the tree to a cooler room, without heat or fans (which can also dry out the air) and the tree’s leaves started growing back immediately.

However, if your kumquat tree is outside and it started dropping leaves, consider if your area recently got a cold or hot spell (under 10ºF or over 100ºF).

Transplant Shock

If your kumquat tree was recently planted or repotted, and it now has leaves dropping, it’s most likely due to transplant shock. Transplant shock occurs when the plant is exposed to a new environment and has to establish a new root system. Avoid transplanting unless necessary as it can take up to 1 year for recovery.

Like many plants, kumquat trees are vulnerable to transplant shock. To help avoid this, I like to plant with the following steps in mind:

  1. Have the new ground (or pot) prepared
  2. Remove as much of the tree’s current topsoil as possible, without damaging the shallow roots
  3. Grab the base of the tree’s trunk and wiggle lightly
  4. Using your other hand, scoop up and support the rootball
  5. Lightly place the tree in the new ground (or pot) and fill it in
  6. Make sure the soil is at the same level on the trunk as before
  7. Apply 2 inches of compost and mulch to the top of the soil
  8. Water generously and add more soil as needed

When planting, take care to avoid thorns! To see which citrus trees have thorns and if you need to prune them, check out my other post here.

Generally, as long as you avoid damaging and breaking the roots, and you keep your kumquat tree comfortable during the move, the amount of stress from transplant shock will be reduced or eliminated.

Pests and Diseases

a ladybug eating an aphid on a citrus tree
A ladybug eating an aphid on a citrus tree. Releasing ladybugs in your garden can be an effective way to get rid of aphids.

Pests and diseases such as aphids, mealybug, and leaf scab cause kumquat trees to lose their leaves. Most pests can be repelled with water, oils, or sprays, while diseases can be treated with organic sprays or fungicides. Some pests and diseases such as nematodes can be deterred with companion plants like marigolds.

While not as common as the other issues on this list, pests and diseases also lead to dropping leaves on kumquat trees.

Generally, you can tell if your kumquat tree has a disease by inspecting the leaves for any brown or yellow spots or deformities.

You can also typically tell if pests are infecting the tree if you see them gathering on the underside of the leaves (like aphids) or boring into the tree (like borers).

If you’d like more information on the common pests and diseases that kumquat trees get, check out this resource by Epic Gardening!

Final Thoughts

So, while improper watering and climate most often cause kumquat trees to lose their leaves, transplant shock, pests, and diseases also cause it.

By only watering when the first 2-4 inches of soil is dry, providing compost and mulch, and keeping your tree in temperatures between 10ºF to 100ºF, you’ll avoid the majority of issues that contribute to leaf loss on kumquat trees.


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