I enjoy growing determinate tomatoes in my container garden. But once I found the leaves were turning yellow. On research, I found that I was over fertilizing my tomato plant.

You can over fertilize a tomato plant by providing excess fertilizer to the soil. Too much fertilizer will cause the leaves to turn pale and yellow. There may be a layer of the fertilizer on top of the soil. You can immediately flush the soil with water to remove the excess fertilizer.

I’ve written a lot more details about the problem of over-fertilizing your tomato plants and how you can avoid it. I’ve also written some details on how you can recover a tomato plant that is suffering from this issue.

What are the signs that your tomato plants are over-fertilized?

Yellowing of leaves

Yellowing of leaves can occur due to other reasons like overwatering, underwatering, pests, and diseases. But if you are sure that you’re watering the plants correctly and the tomato plants are healthy, the yellowing is probably due to over-fertilization.

White material on the soil surface

Another sign that your tomato plant has too much fertilizer is if there is a layer of white material that has developed on the surface of the soil. This is a layer of the nutrients that are being left behind after you water the soil and it evaporates.

Development of thick foliage

If you use a fertilizer that is nitrogen-rich, the sign of over-fertilization is when your tomato plants start growing thick foliage but small fruits. The nitrogen encourages the plant to grow more leaves at the cost of the tomatoes.

Stunted growth of the plant

If you use too much fertilizer that is nitrogen-rich, another problem you may see is the stunted growth of the tomato plants. This happens because the fertilizer burns the plant’s roots causing a lack of nutrients to reach the plant.

How to fix the over-fertilization of tomato plants?

You should be able to recover your tomato plant from over-fertilization if the roots are not too damaged by the problem. Once you recover the plant, make sure not to add any fertilizer to the soil for at least 4 weeks.

Physically remove the fertilizer

If you used dry fertilizer in the soil, you should be able to remove some of it. You can remove the fertilizer on the surface of the soil. You can also remove some of the soil and fertilizer along with it.

Make sure to be careful not to damage the roots of the plant when removing the fertilizer.

Leach the fertilizer by using water

A simple solution to remove fertilizer from the soil is to water it well. This method of leaching works when you keep watering the soil several times so the fertilizer can drain out of the soil. You should use a garden hose that can help flush the soil well with water.

If you’re growing the tomato plant in a container, you can soak the container in water several times to flush out the fertilizer from the soil.

The only problem with this method is the fertilizer will drain into the water sources. If the fertilizer is organic, this should not be a big issue. But if you’re using chemical fertilizer, this can harm other plants, aquatic life, and wildlife.

Mix organic material into the soil

If there’s too much fertilizer in the soil, you can mix organic material like mulch or compost in the soil. This helps balance out the fertilizer and dilute its effect on the tomato plant.

Move the plant to another location

If there’s too much fertilizer in the soil, you won’t be able to remove it physically or with watering the soil. In the worst case, you can move the plant from the current soil to another location with fertilizer-free soil.

If you’re growing the plant in a container, you can take it out and throw away the soil. You can add fresh potting soil to the container and replant the tomato plant.

When to use tomato plant fertilizer?

If you’re growing the tomato plant from seed, you don’t need to add fertilizer till they have germinated. The seeds contain all the required nutrients until the seedling germinates.

Once the true leaves have established, you will need to provide fertilizer so the tomato plant can grow well. If you have amended the soil with organic compost, you may delay adding the fertilizer even further.

I would recommend adding a slow-release fertilizer to the soil when transplanting the seedling. This slow-release fertilizer will release the fertilizer in the soil when you water the plants.

One application of such slow-release fertilizer will last the tomato plant for about one month. You may need to apply such fertilizer 3-4 times during the growing season so the tomato plant can grow well and develop fruits.

The other option is to use a liquid fertilizer that you can spray on the soil and foliage. The benefit of using liquid fertilizer is it immediately gives the tomato plant a boost of nutrients. You need to spray such fertilizer once every two weeks to give the plant the required nutrients.

How to use tomato plant fertilizer?

You need to understand the nutrients in fertilizer and how they help your tomato plants. The main nutrients are nitrogen, phosphorus, and potassium. You will find them written on a fertilizer bag or bottle as NPK (Nitrogen, Phosphorus, Potassium).

Nitrogen is a nutrient that helps grow the foliage of the plant. Phosphorus helps the roots, flower, and fruit development of the plant. Potassium can help keep your plants healthy and strong.

You need to perform a soil test before you can use the tomato plant fertilizer for your plant. If your soil is rich in nitrogen, you need to use a fertilizer that is low in nitrogen. You can use a fertilizer with NPK 5-10-5. If your soil is balanced, you can still use a fertilizer low in nitrogen.

This helps the plant develop the required amount of foliage but have enough nutrients to grow flowers and tomatoes as well.

If your soil is low in nitrogen, you can pick a balanced fertilizer that has equal proportions of nitrogen, phosphorus, and potassium. One such balanced fertilizer would have NPK values of 5-5-5.

If you’re growing the tomato plant in a container, you will be using potting soil that often is sterile. You can treat this as a soil that is low in nitrogen and use a balanced fertilizer.

What is the best fertilizer for tomato plants?

The first thing I recommend adding to your soil is organic compost. This material will provide a lot of nutrients to the tomato plant. It also contains beneficial microorganisms that will improve the soil texture as well as break down the organic material into nutrients for the plant.

You then have a choice of using chemical or organic fertilizer for the tomato plant. They both will work well as the tomato plant cannot differentiate between the nutrients whether from a synthetic or organic source.

I would recommend using organic fertilizer rather than chemical because of some problems they can create. The chemical fertilizer can leach into the soil and harm other plants and wildlife.

organic fertilizer
Organic fertilizer I use for my plants

You need to be very careful using chemical fertilizer because an excess amount will burn the roots of your plants and possibly kill them. The chemicals can also affect the beneficial organisms in the soil and slowly reduce the organic nutrients in the soil.

The best organic fertilizer I would recommend you use for your tomato plant is Dr. Earth Organic Tomato Fertilizer. This is a complete organic fertilizer that also contains beneficial soil microbes and mycorrhizae. It has an NPK value of 4-6-3 which makes it high in phosphorus and low in nitrogen and potassium.

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