Ideal Tomato Soil – Garden Soil Or Potting Mix?

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In order to grow healthy tomato plants and maximize your tomato harvest, it’s important to get your soil right. So what is the ideal tomato soil? Just read on.

Basically, the ideal tomato soil should have the following characteristics:

  • well-draining,
  • holds moisture well (like a sponge),
  • rich in nutrients (either from organic or chemical sources),
  • neutral or slightly acidic pH,
  • free of soil-borne tomato diseases and contaminants.

The ideal soil for tomatoes is either garden soil or potting mix, but the above requirements should be met.

Potting mixes usually contain compost or chemical fertilizer, shredded bark, coconut coir or peat moss, and other soil amendments like perlite or vermiculite which help improve drainage and aeration.

Garden soils are typically comprised of a combination of sand and loam which provide better drainage than clay-based soils but still hold enough moisture for the roots to absorb.

Types Of Soil And Soil Textures

Garden Soil

Tomatoes thrive in loam and sandy loam soils, although they can adapt to various soil types except for heavy clay.

Gardeners have the option of adding materials such as sand, sawdust, peat moss, coconut coir, perlite, or other amendments in order to improve the texture of clay-based soils prior to planting.

The key is to have soil that is loose and well-drained yet still holds enough moisture for the roots to absorb without becoming waterlogged.

Potting Mix

For optimal performance, look for potting mixes specifically formulated for tomato plants that contain compost and additional nutrients for improved drainage and aeration.

Soil pH

Soil pH is an important factor to consider when growing tomatoes, as it affects the availability of nutrients for the plant.

To ensure optimal growth of tomatoes, it is recommended to plant them in soil with a pH level of 6.5-7.0, which may require adjusting the soil’s pH.

It is important to test your soil and make any adjustments before planting tomatoes, as any significant changes made after planting can damage the roots and reduce yields.

Increasing pH: it is recommended to add agricultural lime to the soil prior to planting.

Decreasing pH: utilize elemental sulfur or fertilizers containing ammonium sulfate.

Nutrients & Fertility

To ensure that your plants have a steady supply of nutrients. If you walk the organic path, you should incorporate compost into the soil before planting. Compost contains essential minerals and helps to improve drainage and aeration.

You can also supplement the soil with an all-purpose fertilizer containing potassium and phosphorus.

It is recommended to avoid fertilizing with high nitrogen content, as it may cause excessive foliage growth and negatively impact fruit production.

Tomatoes require a relatively lower amount of nitrogen (N) and a higher amount of phosphorus (P) and potassium (K). The ideal NPK ratio is 5-10-5.

However, if your soil lacks nitrogen, you can use a fertilizer with a 10-10-10 NPK ratio.

Hint: Alfalfa meal is a natural, slow-release fertilizer that provides a high amount of nitrogen. The slow-release nature of Alfalfa meal ensures that the nitrogen is released gradually over time, providing the plant with a consistent source of nutrients.

Potting Mixes

Look for mixes that contain a blend of organic matter, soft matter, and hard matter such as compost, peat moss, and vermiculite, respectively.

These materials help retain moisture and improve drainage while providing essential minerals and micronutrients that plants need to grow healthy and strong. Also, check the NPK designation of the mix (5-10-5 is recommended).

Moisture Level

Tomatoes need consistent moisture levels for healthy growth. Provide enough water to keep the soil moist, but not soggy.

The best way to ensure adequate moisture levels is by using a well-draining potting mix such as one that includes peat moss, coco coir, coarse vermiculite, or a combination of these.

These materials help retain moisture while allowing water to drain away from the roots of your tomato plants, preventing root rot or other problems caused by over-watering.

If planted in the garden soil, weekly deep watering may be enough, but when it gets dry and hot, more frequent watering may be needed. It’s best to check the soil moisture regularly to make sure the plants are getting enough water.

Additionally, mulching around the base of tomato plants provides insulation and helps maintain consistent soil temperatures and moisture levels for healthier growth and better yields.

Soil Temperature

The ideal soil temperature for tomatoes is between 65-70°F (18-21°C).

If the soil is too cold, tomatoes will take longer to germinate and young seedlings won’t thrive. If the soil is too hot, it can cause the plants to wilt and be less productive.

Note: Tomato seeds will germinate at even 50°F (10°C), but it may take over 40 days. At soil temperatures above 100°F (38°C), no germination is likely.

Organic Soil Mixes

Organic soil mixes are a great choice to grow tomatoes in an eco-friendly manner. These products are certified by OMRI, meaning they meet specific criteria for organic gardening, such as being free from chemical and synthetic pesticides, herbicides, and fertilizers.

One of the key benefits of using organic soil mixes with natural ingredients is that they are rich in nutrients. Compost, for example, is a great source of nitrogen, phosphorus, and potassium, which are essential for healthy plant growth.

Organic soil mixes also contain essential minerals and beneficial microorganisms, such as mycorrhizae, which can help plants absorb nutrients more efficiently and improve overall soil health.

Another advantage of using organic soil mixes is that they are typically lightweight and well-draining and also tend to hold moisture well, which can help to reduce the need for frequent watering.

When choosing an organic soil mix for your tomato plants, look for products that are specifically formulated for vegetable or even tomato gardening.

These mixes will typically contain higher levels of nutrients and organic matter (e.g. compost, forest humus, earthworm castings) than standard potting mixes. You can also make your own organic soil mix by combining compost, peat moss / coconut coir, and vermiculite / perlite in equal parts.

Amending Your Soil To Grow Strong And Healthy Tomato Plants

If your garden soil lacks some nutrients or has an unfavorable pH level, it’s recommended to amend it before planting tomatoes.

You can use a soil test kit to determine the pH level of your soil and take any corrective measures needed if required.

As mentioned earlier, tomatoes prefer slightly acidic soil or neutral soil with a pH range between 6.5 and 7.0. If your soil is too alkaline, you can add sulfur to lower the pH. If it’s too acidic, you can add lime to raise the pH.

Next, you’ll want to add nutrients to your soil. Adding garden compost or manure is an effective way to add organic matter and essential minerals to the soil.

  • You can add fish emulsion, urea, or blood meal for additional nitrogen.
  • Epsom salt is another great addition, as it provides magnesium.
  • Burned eggshells are a great source of calcium (for avoiding blossom end rot).
  • Rock phosphate and bone meal contain a lot of phosphorus.
  • Wood ash is high in potassium.
  • Kelp meal is a rich source of micronutrients, macronutrients, and amino acids. Kelp contains natural alginate that can effectively amend the texture of the soil by binding soil grains together.

Note: Fresh manure, which has not been composted, can potentially harm plants due to the presence of excessive salts.

Additionally, adding organic material like composted leaves, straw, grass clippings, and wood chips can help improve soil drainage and air circulation which are both essential for growing healthy tomatoes.

Finally, don’t forget to add mulch around your tomatoes to help maintain consistent soil temperatures and moisture levels.

Different Soils For Different Growth Stages?

You may wonder if it is necessary to use different soils for different growth phases of your tomato plants. Basically, one potting soil mix, fulfilling the requirements mentioned earlier, may be enough for each stage of growth.

However, for seed starting you can use a medium not containing nutrients at all. Then transplanting your young seedlings into a good quality vegetable potting or planting mix is recommended.

Finally, after another transplanting, your plants can be grown throughout the season in either the same potting mix in larger containers or in the garden soil.

In both cases, you may need to add fertilizers until the end of the season to maximize yields.

The table below summarizes which kind of growing medium is suitable for the different growth stages.

Seed Starting MediumSeedling Planting MediumTomato Plant Growing Medium
Pure VermiculateCommercial Planting Mix For VegetablesCommercial Potting Mix For Vegetables
Pure PerliteHome-made Planting Mix (e.g. peat moss + vermiculite + compost)Home-made Potting Mix (e.g. peat moss + vermiculite + compost)
Pure Sphagnum Peat MossPure CompostPure Compost
Pure Coconut CoirGarden Soil (in the case of direct sowing—growing tomatoes from seed in the garden soil)Garden Soil (in the case of direct sowing—growing tomatoes from seed in the garden soil)
Some Mix Of The Above, e.g. 1/2 Vermiculate + 1/2 Peat Moss OR 1/2 Perlite + 1/2 Coconut Coir  
Pure Compost  
Garden Soil (in the case of direct sowing)  

FAQ About The Ideal Soil For Tomatoes

Which Soil Is Best For Growing Tomatoes?

The ideal soil for tomatoes is well-draining, rich in nutrients, has neutral or slightly acidic pH, can hold a lot of water, and has no soil-borne tomato diseases or contaminants.
For container gardening, you can use a soilless, ready-made potting mix for vegetables (available at garden centers)—it’s probably the simplest way, but in larger quantities, it can be costly.
You can also prepare your own growing mix, a good combination is equal parts of vermiculite, sphagnum peat moss, and mature compost.
If you plant into your garden soil, make sure it drains well, it’s rich in organic matter, and it’s free of diseases (apply crop rotation: don’t plant in soils that have grown nightshades, i.e tomatoes, potatoes, peppers, or eggplant in the past 2-3 years).

When Should I Fertilize My Tomato Plants?

Generally speaking, fertilizing your tomato plants every two weeks will help ensure they receive enough nutrients throughout their growing season.
It’s best to use an all-purpose fertilizer that contains nitrogen, phosphorus, and potassium in proportions of 5-10-5 so that your plants have access to all the necessary nutrients for strong growth and abundant fruit production.

How To Choose A Good Quality Growing Mix?

You’ll need a growing medium that drains well, contains a lot of nutrients, and keeps moisture like a sponge. These usually contain sphagnum peat moss / coco coir, perlite / vermiculate, compost / chemical fertilizers.
Avoid choosing a mix that doesn’t list the ingredients.
We recommend organic growing mixes specially developed for growing tomatoes. Chemical fertilizers may also work well, but are usually not environmentally friendly.

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AUTHOR

I'm a keen hobby gardener. I love growing fruits and vegetables, especially tomatoes. I'm also a certified instructor of the Square Foot Gardening Foundation.