Tomato Nutrition: Feeding for Success

Tomato plants are easy to grow but they are heavy feeders so you must feed them well. They are quick to show nutrient deficiencies by exhibiting decreased growth and often changes in appearance. This guide offers you all you need to know about properly feeding your tomato plants to achieve the best crop. Some common deficiencies and how to fix them will also be covered.

Photo by Chad Stembridge on Unsplash

Prepping before planting

As always, the best way to ensure that your tomato plants are fertilized correctly is to start with the right soil. Be sure to properly amend with compost or manure for nitrogen as tomatoes are heavy feeders. Products like blood and bone meal can also add nitrogen plus calcium for root growth. Kelp meal and soil mineralizers like crushed shale can also greatly increase the mineral and micronutrient contents of the soil for long-term benefits to your plants. Soil may be lightly top dressed with compost and manure

throughout the growing season to ensure a steady supply of nitrogen. It is also important to note that your soil pH should be slightly acidic (7-6) to grow the best tomatoes. This pH level allows for proper uptake of the nutrients you are feeding to your plants. Adding more organic material (like compost) helps lower the pH of the soil and keep it there. On the other hand, if your soil is more acidic (lower) than 5.5, you will need to add some horticultural lime or wood ash to raise the pH. 

Growing with the plant

One of the mistakes people often make when feeding tomatoes is giving their tomatoes the same composition of fertilizer throughout the growth of the plants. The best fertilizer regime for tomatoes is one that changes with the plant itself. At the beginning of its life, a tomato needs more nitrogen and phosphorous for green growth and root growth. As the plant gets larger, it will need more potassium to encourage flowering and fruiting. At this point, switch to a balanced fertilizer where all three numbers are the same. Once fruit begins setting you want to maximize fruit size and promote more flowering. Use a bloom booster fertilizer where the third number (which represents potassium) is higher than the other two numbers. The recommendation would be to alter this with a balanced fertilizer while plants are still growing as fertilizers too high in phosphorous can cause nitrogen deficiencies.

Foliar feeding

Tomato plants have an abundance of leaf area, which provides a great opportunity for foliar feeding. Foliar feeding is a great way to ensure your plants are getting all the micronutrients they need as many of them are absorbed more readily through the leaves. Foliar feeding can be done with any fertilizer diluted to at least 4-4-4 to prevent burning. Foliar feeds at this strength are best used monthly. Many products (such as kelp fertilizer) that are known to have lots of micronutrients are often mixed to low strength levels (usually 0.5-0.5-0.5 range) and used weekly. Even a couple of foliar feeds in a summer make a huge difference in the appearance, growth and overall health of your plants. Foliar feeding is especially helpful in speeding up the growth of young transplants or seedlings.

Identifying and Understanding Deficiencies

Despite all the careful prepping and feeding, your tomatoes may sometimes get nutrient deficiencies. The good news is that most of these, especially the common ones, are easily identifiable and quickly fixed. Below are some of the most common problems and their remedies. A healthy tomato plant is a medium green and the same color all over. Note that determinate tomatoes will start to show discoloration and dieback as they set fruit and stop growing. There is no amount of feeding that can prevent this.

Nitrogen deficiency is characterized by the youngest growth on your plants being apale yellow color. This is caused by not enough nitrogen being available to your plant. In older plants that have been growing for a while, this is usually due to there not being much nitrogen left in the soil. The quick fix is to apply a balanced or high nitrogen fertilizer or top dress with fresh compost or manure. In any age plant, the application of too much high phosphorus fertilizer can prevent proper nitrogen intake and cause deficiency.

Phosphorus deficiency is characterized by stunting and purpling of the leaves, particularly the undersides. Purpling usually shows up first in older leaves. It can be tricky to identify this common deficiency but if your tomatoes are not doing well for no apparent reason, giving them a higher dose of phosphorus (such as a rooting fertilizer) may help. Foliar feeding is very helpful in avoiding phosphorus deficiencies.

Iron deficiency is characterized by an overall yellowing, and eventual bleaching, of all the plant leaves except the veins. This condition starts with the youngest growth closest to the stem. It is usually caused by soil decomposition. When soils or potting mixes are over amended with organic matter which is not fully composted, or when the soil is wet, the soil becomes anaerobic. Hold back on the watering and apply some iron fertilizer, or try applying the water left from cooking beets or spinach. Another cause of iron deficiency is too much heavy metal in the soil. This is common in clay soils and soils too rich in calcium. Amend with well-composted organic matter and apply an iron supplement. 

Homemade Supplements

There are lots of things you have around the house that can be utilized in growing the healthiest tomato plants. While not necessary, adding these materials to the soil while plants are growing will help keep tomato plants happier and healthier.

Coffee grounds make a great top dressing around tomato plants. They release nitrogen and micronutrients into the soil as they break down. They also help acidify the soil – which tomatoes love – and they help make other nutrients more available.

Eggshells are a great addition to the soil around tomatoes. As they break down they release potassium and calcium which helps to promote strong root growth and flowering.

Epsom salts are a magnesium salt. When applied at a rate of one half Tablespoon per plant at the time of planting, they help prevent transplant shock. They may also be applied monthly beginning just before flowering.

Veggie juices from cooking veggies like beets, chard, asparagus and spinach have micronutrients and iron in them that tomatoes love. Don’t pour it down the drain. Pour it on your plants! 

Photo by Sven Scheuermeier on Unsplash

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