Summertime is the tomato growing season! Even though growing tomatoes is relatively simple, the choice of the right high-quality soil for tomatoes in pots should be taken seriously. The taste of your tomatoes can vary significantly depending on what kind of potting soil and plant food you use.
We will cover some factors and aspects that you should consider when picking a potting mix or a fertilizer for growing tomatoes, and we will also give you some examples of good potting soils that are not expensive. Best soil for tomatoes in pots:
What Does the Best Potting Soil for Tomatoes in Containers Look Like?
Tomatoes grow well in most types of garden soil. The kind of soil that you should avoid using for tomatoes is clay soil. Due to its high density and water retention, root growth is obstructed.
Tomatoes prefer soil with good drainage and enough water retention to fulfill their moisture requirements. Soil with lots of organic materials will be great too.
So the perfect potting soil for tomatoes would be well-aerated, well-drained but moisture-retaining, full of organic matter and nutrients. It should have higher levels of phosphorus and potassium along with a slightly acidic soil pH level of 6-6.8.
The way of growing tomatoes will also affect your decision. If you plan to start the seeds in soil, you should aim for much lighter potting soil mixes. When planting tomato seedlings, a denser kind of soil is used.
Let’s start with particular factors you should consider while choosing a potting mix for your tomato plants.
Key Factors When Preparing Soil for Container Tomatoes
1. Container Size and Soil Amount for Potted Tomatoes
The container should be at least 5 gallons large. A 10 gallon container would be ideal. A wider container is preferred for growing tomatoes because their roots grow more wide than deep.
2. Optimal Soil Depth for Tomato Root Development
As mentioned earlier, tomatoes’ roots don’t grow very deep down, they usually spread out instead. The core root system of a tomato plant is located within the first foot below surface. So, a soil depth of 8-12 inches is enough for potted tomatoes.
You should loosen the soil all the way down using a trowel to get the best aeration. If you transplant a young tomato plant into a pot or container, you want to put it at least 3-4 inches deep. This way the plant will be stronger once the roots grow out.
3. Essential Potting Mix Components and Soil Additives
You cannot just fill your container for tomatoes with garden soil, because it drains too quickly, you would have to water it several times a day. Garden soil is also more easily compressed over time, which is bad for tomato roots.
Just like with houseplants, you want to use commercial potting mix for growing tomatoes or make such mix on your own. As an option, you can take some well-suited potting soil and mix it with the soil from your garden, which will give you a good amount of substrate.
Commercial potting mixes usually include ingredients that improve drainage, water retention ability, porosity, pH balance and other factors. Most common of them are listed below:
- Peat moss. It’s usually the main component in potting soils including tomato and vegetable blends. Peat moss absorbs water and gradually releases it over time to keep the tomato roots wet.
- Coco coir. It is a peat moss alternative. Coir prevents soil compression, absorbs moisture and releases it slowly to keep plants roots wet, the way that moss does it.
- Bark. It is harvested from pine or fir trees. Bark helps make the potting soil less dense and more aerated so the roots have more room to grow and more access to the air.
- Perlite & vermiculite. These are both byproducts of volcanic glass. Perlite makes soil more porous and aerated, preventing soil compaction. Vermiculite acts in a similar way, but it tends to retain more moisture. So good horticultural grade perlite should be used for tomatoes, because they prefer a less moistened environment.
- Sand. Horticultural sand can be used in soil to improve drainage. It can also strengthen the soil structure so roots can be anchored more easily. This way tall tomato plants will not fall over.
- Wetting agent. Some potting soils are semi-damp when packaged and others are completely dry. You can face some problems while moistening dry peat moss mixes for the first time: the moss floats rather than absorbs water. Wetting agent helps the moss absorb water during the first moistening. After that the moss has no problem absorbing water.
- Earthworm castings. They act more like a fertilizer. Earthworm castings are worm feces that contain nutrients and beneficial bacteria and are found in many mixes.
Here are some factors that affect tomato growth and development:
4. Best Soil Type for Container Tomato Plants
Tomatoes can grow in most potting soils except clay soils which happen to be too heavy. A loose soil is optimal for tomato plants.
5. Ideal Soil pH Level for Growing Tomatoes
The ideal pH level for tomatoes is 6.0 to 6.8 (slightly acidic). Tomatoes can still grow in the range of 5.5 to 7.5. Potting soil that contains some organic materials like dried leaves or compost usually matches this range.
Not every commercial potting soil comes with its pH level written on the bag. You can easily determine pH of the soil with a cheap soil tester available at any garden center or on Amazon.
6. Proper Moisture Level and Drainage Requirements
Tomato roots don’t like it is high or low. The potting soil for tomatoes is supposed to be well-drained so it stays moist but not too soggy. Soil that is too damp will cause root rot.
That’s why it is advised to have some coco coir, peat moss or perlite in the soil mix.
7. Essential Nutrients and Fertilizer for Tomato Plants
Make sure your tomato plants have a constant supply of food during the whole season. Tomatoes generally love lots of nutrients. They need the soil to be rich in organic matter and micronutrients such as phosphorus, potassium, calcium and magnesium.
Phosphorus and potassium promote flowering and help growing healthy tomatoes. A sufficient level of Calcium helps inhibit blossom end rot.
That’s why tomato fertilizers are high in phosphorus. You can see that in the middle number of the product’s nitrogen (N), phosphorus (P), and potassium (K) ratio. This number is high compared to the other two numbers, for example, 8-15-6 or 5-7-3.
As mentioned before, tomatoes’ flavor is greatly affected by the potting soil you plant tomatoes in, so make sure you place your tomatoes in a nutrient-rich organic soil!
Summary of Best Soil Requirements for Potted Tomatoes
The perfect soil for potted tomatoes is a loose soil that holds enough water to prevent the roots from drying out, contains lots of potassium & phosphorus, and has a pH level of 6-7.
DIY Potting Soil Recipe for Container Tomatoes
If you actually want to prepare your own potting soil mix instead of buying one, here’s a short recipe that uses the ingredients we’ve talked about before:
- 25% Garden soil or topsoil from your backyard. Make sure it does not have a high level of clay in it. If your soil is too clayey then try to lower its quantity and add more perlite and coco coir to the mix, also loosen the soil and break all the clumps before mixing.
- 25% Perlite/Vermiculite
- 25% Coconut coir/Sphagnum peat moss
- 25% Compost/Decomposed cow manure or some organic components such as leaves, vegetable scraps, etc.
Important Warning About Using Garden Soil
Using your garden soil is risky as it can contain weed seeds, insect eggs and larvae, fungi and other pests which can cause disease in your plants. That is why you should sterilize the soil before using it.
If you don’t want to make your own soil, you can always buy a commercial potting mix.
Top 8 Best Commercial Potting Mixes for Container Tomatoes
1. FoxFarm Ocean Forest FX14000 Organic Potting Soil (may be the best potting soil in general)
This rich in organic matter mix is perfectly suited to growing tomatoes. It has a good balance of peat moss, sandy loam and forest humus. Ocean Forest provides tomato plants with ideal drainage and no soil compression over time.
It can retain moisture long enough between waterings too. The additives in the soil mix are natural ingredients, such as bat guano, fish and crab meal, earthworm castings. Ocean Forest has a suitable pH level of 6.3 – 6.8, which is just what tomatoes need.
