Tomato Plant Fertilizer: How to Fertilize Tomatoes for a Great Harvest
Tomatoes are hungry plants with relatively shallow root systems that depend very much on a constant stream of water and nutrients to bear healthy and tasty fruits in larger quantities.
From the seed germination to the harvest, nutrient-rich, moist and well-aerated soil with proper pH is of utmost importance for having strong and healthy tomato plants. This may sound complicated, but actually, it is not - and it can be a very pleasant task to the care of your own plants while watching them grow, flower, and ripen ...
Published: February 24, 2022.
On This Page:
- Best Soil For Tomato Plants
- How to Fertilize Tomato Seedlings
- How to Prepare the Garden Soil
- Fertilizing the Planted Tomato Seedlings
- Fertilizing the Flowering Tomato Plants
- Fertilizing the Tomato Plants During Harvest
- Mulching the Tomato Plants or Not
- Few Final Words
Best Soil For Tomato Plants
Tomatoes prefer light, well-aerated, slightly acidic soil with a pH range of 6.0-6.7.
Soil should ensure good drainage since tomatoes don't like soggy feet, but the soil should also be kept moist - constant moisture and a constant supply of nutrients ensure the proper development of healthy plants and fruits.
In the case of sudden spikes in moisture and nutrients, tomato plants may grow weak and prone to diseases, can develop very few flowers, while the fruits can grow irregularly.
In the case of heavy soils, one can add some sand and peat moss to the soil to improve the drainage.
Since tomatoes prefer nutrient-rich soil with plenty of organic matter, adding some worm casting, compost, and/or dried manure can improve the quality of the soil - as the organic matter decomposes, it ensures a constant amount of nutrients in the soil but also increases the amount of good soil bacteria and earthworms, which improves the quality of soil in the long run, too.
In order to fertilize tomatoes properly, one must be aware of the most important plant nutrients required by tomatoes:
- Nitrogen (N): nitrogen is very important for plant growth and foliage. In nitrogen-poor soil tomato plants grow weak and slow, without much foliage. On the other hand, too much nitrogen can cause the rapid growth of tomato plants, making them susceptible to diseases and pests.
- Phosphorous (P): phosphorous is very important for root and fruit growth. In phosphorous-poor soil, plants grow weak and are very much prone to diseases and pests.
- Potassium (K): potassium is important for general plant growth and for the growth of flowers and fruits. Also, it plays a vital role in photosynthesis and improves tolerances to some diseases.
Nitrogen, phosphorous, and potassium (N-P-K) are important for proper tomato plant growth but don't forget the long list of so-called micro-elements that are also very important not only for tomatoes but other plants as well. These micro-elements include calcium, sulfur, iron, magnesium, manganese, molybdenum, etc.
In short, tomatoes prefer fertilizers that feature moderate amounts of nitrogen and are rich in phosphorous and potassium. Also, such fertilizers should contain all the required micro-elements.
So, in order to avoid a shortage of any macro- and micro-nutrient, it is very important to prepare the soil properly and to add fertilizers when required.
Note: too much fertilizers can cause burns and can easily kill tomatoes and other plants. When applying the fertilizers, be sure to follow the instructions.
How to Fertilize Tomato Seedlings
Tomato seedlings grow happily in the standard potting soil mix, however, in order to promote growth, adding a little bit of organic tomato fertilizer or worm castings can improve the growth, especially the growth of the root system.
If You have purchased tomato seedlings from the local garden center, and if You don't plan to replant them right away on their permanent location, feel free to add a weak dose of organic fertilizer or worm castings into the pot and mix it a little bit with the potting mix.
How to Prepare the Garden Soil
Before the tomato seedlings can be planted on the permanent location, it is necessary to prepare the soil.
If You have time in the autumn, clean the patch of soil from the old leaves, roots, branches, and similar debris, add a good amount of aged manure and mix topsoil down to 8-10 inches, or even slightly deeper.
Tomatoes don't have a deep root system - 6-8 inches (15-20 cm), rarely deeper (depending on the variety, size, and age of the plant and similar), but mixing the soil deeper than that improves the drainage, among other things.
In spring, again, clean any debris from the patch and add organic fertilizers that slowly release the nutrients and that improve the soil quality in terms of moisture retention, drainage, and similar.
So, feel free to add some peat moss, worm castings (practically odorless), aged manure (aged manure in pellets is almost odorless), organic compost, and some organic fertilizer for tomatoes with a moderate amount of nitrogen, but rich in phosphorous and potassium.
Organic fertilizers for tomatoes come in various forms, including granules, fertilizer spikes, and liquid fertilizers.
Fertilizers in granules are the best for mixing with soil prior the planting, especially ones with gradual release of nutrients that feed the plants for months.
Fertilizer spikes can be added prior to the planting or during the growth - the user has to simply insert the spikes into the soil near the plants every 1-3 months (plant and fertilizer dependent).
Liquid tomato fertilizers are excellent for nourishing plants during the growing season. But, liquid fertilizers must be added carefully to avoid burns and they must be added continuously every 1-2 weeks.
Personally, if the soil is prepared well, adding some worm casting, compost, and organic tomato fertilizer during the growing season is more than enough even for hungry plants like tomatoes - organic tomato fertilizers generally have low amounts of NPK, but they are rich in organic matter, they improve the structure of the soil and as the organic matter decompose, it keeps the amounts of nutrients rather constant.
However, if You do notice that your tomatoes are not growing as they should, liquid organic tomato fertilizers are an excellent choice for quickly improving the soil.
But, if You are unsure why your tomatoes and other plants are not growing as they should, use a home soil test kit to check the soil first - maybe there are more than enough nutrients in the soil, but some other reason is preventing the plants from growing properly.
Soil test kits can be found in local garden centers, or they can be ordered from online shops.
For the most up-to-date offers and prices, feel free to check the Soil Test Kit Amazon link (the link opens in the new window).
Fertilizing the Planted Tomato Seedlings
When the tomato seedlings are planted on the permanent location, the soil is prepared - it is rich in all required macro- and micro-nutrients and organic matter.
However, even if the gardener didn't have time to prepare the soil, it is a good practice to add a small amount of organic compost, or worm castings, or organic tomato fertilizer in the planting holes and to mix everything with the soil.
Also, adding some peat moss can improve drainage and help the soil retain moisture.
So, plant the tomato seedlings and add tomato supports right away - adding supports later can damage the roots.
Water the plants and let them adjust to their new environment for at least 2-4 weeks, after which one can add, if required, some liquid fertilizer to help the growing plants.
Fertilizing the Flowering Tomato Plants
Flowering tomato plants require plenty of potassium and phosphorous to form a large number of flowers and to grow fruits.
When the soil is properly prepared, there is no need to add much additional fertilizer - but, since the tomatoes have a shallow root system and because they can grow quite vigorously with plenty of flowers and potential new tomato fruits, it is a good practice to add a small amount of the time-release organic fertilizer into the soil, or some worm casting or similar organic fertilizer.
In the case that the soil wasn't well prepared, organic liquid fertilizers can be added every 1-2 weeks - even if the soil was well prepared, a really small amount of organic liquid fertilizer can help keep the nutrients at required levels before the nutrients from other fertilizers kick in.
As the small tomato fruits grow, plants need potassium and phosphorous - as the organic matter decomposes and as time-release tomato fertilizers release the nutrients, plants are growing happily.
Fertilizing the Tomato Plants During Harvest
Depending on the variety, tomato plants can have a rather long harvest. However, too much fertilizers during the harvest can cause plants to grow foliage and not so much tomato fruits.
When the harvest starts, the soil should still be rich in organic matter - if not, again, add some (but not much) organic slow release tomato fertilizer and perhaps a little bit of liquid tomato fertilizer.
If the harvest is short and the soil was prepared properly and the tomato plants were fertilized 2-3x during the growing season with slow-release fertilizers, there is really no need to fertilize the plants anymore.
Mulching the Tomato Plants or Not
Using organic mulch can protect the topsoil from the sun and strong wind and can help with retaining moisture.
Also, organic mulch decomposes over time, refeeding the plants.
Some people prefer to add mulch to the tomatoes and some don't - personally, I prefer to actually see the soil and its condition. Also, as the tomatoes grow, they keep the soil in shade, protecting it from the strong sun.
Without the mulch, it is also much easier to add some organic fertilizer to the soil - just spread it on the soil surface and till it an inch or two into the soil very carefully in order not to damage the root system.
Again, this is highly personal.
Few Final Words
Keeping the tomatoes happy and in good condition should not be a problem. If You want to grow tasty and juicy tomatoes, be sure to have some worm castings and/or organic, slow-release tomato fertilizer.
When preparing the soil, peat moss, worm castings, compost, pelleted manure, and even some sand can be very useful - again, there is no need to add everything on this list, just be sure to end with the soil that is rich in organic matter, well-aerated, that drains well and retains the moisture.
Liquid tomato fertilizers can come in very handy on too sandy soils and when the gardener didn't have time to prepare the soil properly - or when plants simply require more nutrients.