How to Fertilize Indoor Citrus Trees (Essential Tips)

Citrus trees like Meyer lemons and kumquats brighten your home with evergreen leaves and provide a harvest of juicy fruits. However, these plants need a bit of help to stay healthy. All types of indoor citrus trees are heavy feeders, so you’ll need to apply fertilizer regularly along with providing them with ample light. In this guide, I’ll run through everything you need to know about how to fertilize indoor citrus trees properly.

Fertilizing Indoor Citrus Trees – The Essentials

For optimal growth and bountiful harvests, indoor citrus trees thrive best with a fertilizer that has a balanced NPK ratio; 6-3-3 and 4-3-4 are good ratios. Follow package instructions to apply this fertilizer three times a year in February, May, and August.

Why Fertilizer is Important for Citrus Trees

Along with requiring water and carbon dioxide, plants also need nutrients. Some of these nutrients act as the building blocks for plant tissue and others help plants complete essential processes.

Fertilizers can be made from organic materials like fertilized chicken manure, rock dust, and seaweed. They can also be made from human-synthesized materials such as ammonium nitrate.

Whether you choose organic or synthetic fertilizers, you must apply a fertilizer that supplies all the nutrients your citrus tree needs. Here’s a quick rundown of some of the most essential nutrients for citrus trees.

• Nitrogen (N) is the building block of many plant proteins and enzymes. Citrus trees require a hefty dose of this macronutrient.
• Phosphorus (P) plays a significant role in energy transfer, protein synthesis, and the formation of new tissue.
• Potassium (K) isn’t found in plant tissue itself, but it’s essential for various plant processes. Your citrus tree will appear weak without enough potassium.
• Magnesium (Mg) is a significant part of chlorophyll and also helps with plant metabolism.
• Sulfur (S) helps form amino acids, oils, and vitamins.
• Calcium (Ca) plays a major role in cell wall and cell membrane development.

Along with these six macronutrients and secondary nutrients, there are also numerous micronutrients. These are all also important to plant health, but plants require them in smaller doses. Zinc and iron are especially important.

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Signs Your Citrus Tree is Lacking Nutrients

Since different nutrients perform various roles in citrus trees, nutrient deficiency can appear in multiple forms. Here are some ways to tell your plant may be lacking essential nutrients.

Yellow Leaves

Yellowing and/or dropping leaves are common symptoms of nutrient deficiency. If you notice older leaves turning entirely light green then yellow, it’s likely your tree is lacking nitrogen.

Pests, bugs, and nutrient deficiencies can also lead to yellowing leaves in citrus trees. If you notice the tips of older leaves turning yellow, your tree may be lacking magnesium. Without applying this nutrient, these leaves will develop large yellow v-shaped discolorations.

A lack of iron, zinc, sulfur, potassium, and manganese can also cause leaf discoloration.

Additionally, keep an eye on the temperature and humidity to ensure your citrus plant is situated in an appropriate location.

For more, see our in-depth guide to pruning indoor citrus trees for cutting back old or decaying leaves and branches, and consider repotting if your tree needs additional room to grow.

Small Fruit

If your plant is producing smaller fruit than it should be, it might not have access to enough potassium. A lack of calcium can also lead to small fruit.

A Lack of Fruit

If your plants are mature enough to fruit but aren’t producing blooms, your fertilizer could be to blame. While nitrogen is essential for plant growth, too much nitrogen can lead to a lack of flowering. Try switching to a fertilizer with more phosphorus and potassium relative to the amount of nitrogen.

Poor Quality Fruit

If your citrus tree produces fruit with thick rinds and not much juice, your plant probably needs more phosphorus. Boosting your phosphorus fertilizer will improve fruit quality.

When and How Often Should You Fertilize Indoor Citrus Trees?

You should fertilize your citrus tree three times per year. The first application should occur in February, the second May, and the third in August.

The Best Fertilizer for Indoor Citrus Trees

Citrus trees need a fertilizer that provides a large dose of nitrogen and similar amounts of phosphorus and potassium. Make sure to look at the NPK ratios on products to see that the product contains at least as much nitrogen as it does potassium and phosphorus. Ratios like 6-3-3 and 4-3-4 are good options.

Fertilizers should also provide secondary nutrients and the micronutrients iron and zinc.

While you can mix different fertilizers together to form a good fertilizer blend, buying a pre-mixed fertilizer is easier. Fortunately, it’s easy to find fertilizers specifically designed for citrus trees.

All of the following options will work well for citrus trees:

• Espoma Organic Citrus-Tone
• Down to Earth Citrus Mix
• Miracle-Gro Shake N’ Feed Citrus, Avocado, Mango Plant Food
• Jobe’s Fertilizer Spikes for Fruit and Citrus

When you’re applying fertilizer, make sure to follow product instructions. Many products list the annual application rate, so divide this number by three if you’re fertilizing three times per year.

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How to Apply Fertilizer

Fertilizer application depends on the type of fertilizer.

To apply granular fertilizer, follow these steps.

1. Measure out the proper amount of fertilizer.
2. Water the soil well.
3. Apply the fertilizer in a band a few inches away from the base of your tree.
4. Mix the fertilizer in with the top inch of potting soil.
5. Water the soil again.

To apply fertilizer spikes, follow these steps.

1. Measure the diameter of your plant.
2. Using the package instructions and your plant’s diameter, set aside the proper number of spikes.
3. Insert the spikes into the soil so the tops are flush with the soil surface. Make sure the spikes are evenly spaced around the plant.

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Key Considerations

Along with choosing the proper fertilizer and applying it at the correct time, you should also keep these considerations in mind.

Avoid Fertilizing New Trees

If you just brought a tree home from the store, there’s a good chance the tree has recently been fertilized. Many growers add a slow-release fertilizer to keep the tree healthy as it waits for a home.

With this in mind, you should avoid fertilizing your new tree for the first two months.

Don’t Over Fertilize

While citrus trees need fertilizer, too much fertilizer can cause serious harm. When in doubt, it’s safer to underapply rather than overapply.

If you do end up applying too much fertilizer at once, your plant may show an adverse reaction. Since many types of nutrients are salts, too much fertilizer can lead to a salt injury. Symptoms of salt injury include leaves with crisp edges, bronze leaves, reduced flowering, and dropping leaves.

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Fertilizing Indoor Citrus Trees FAQs

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Wrapping Up

Remember to fertilize your citrus trees three times a year with a properly formulated fertilizer. By spending a few minutes caring for your plants, you’ll be rewarded with lush greenery and juicy fruits.

For more, see our in-depth guide to the meaning and symbolism of citrus trees.

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