Best Soil for Tomatoes | pH, Amendments, Potting Mix

There isn’t a more delectable, summer activity than walking into your veggie patch, picking a ripe tomato right off the vine, and taking that first juicy bite.

Most tomatoes used to be yellow or orange but, through selective breeding, evolved into today’s familiar red. Fortunately, ‘heirloom’ seeds from those originals were collected and preserved.

Regardless of your chosen tomato variety, a plentiful harvest requires the perfect growing environment. Each stage of a tomato plant’s growth requires slightly different care in order for it to be healthy and productive. This process starts from the ground up… literally!

In this article, I’ll teach you about the best soil for tomatoes, including how to make your own high-performing blend.

Best Soil for Growing Tomatoes 

According to the University of New Hampshire, the flavor profile of a tomato is extremely dependent on the composition of the soil. Weather plays a part, too. 

Now, tomatoes will grow in just about any kind of soil except clay. (Tomato plant roots simply can’t push their way through heavy-clay soil.) But a tomato plant’s performance will be equal to the quality of the soil it grows in. 

Your soil should be well-draining and loamy with a pH of 5.8 to 7.0. Contrary to common beliefs, adding sand or peat will not enhance flavor or soil fertility. Amending the top 6 to 10 inches of soil with organic compost, quality topsoil, and other beneficial additives will create the best environment for your tomatoes. I recommend purchasing an at-home soil test kit to check the pH, or even sending a sample off for a lab test.

tomato in greenhouse

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Greenhouse Vs Containers 

Containers are a fantastic way to grow tomatoes if you’re limited to a small space. But container-grown tomatoes require more frequent care and, being out in the open, are more prone to pests and environmental stressors.

The environment that a greenhouse offers is a little different. Clear panels intensify natural sunlight and warmth, which promotes increased photosynthesis and vigorous growth. Fans can be installed to cool things down on particularly hot days. But greenhouse plants are also grown in containers, which means even more frequent care. On the bright side, all this effort leads to an abundance of near-perfect tomatoes. 

Soil Recipe for Tomatoes In Raised Beds 

Quality soil is your first step toward a bountiful harvest, whether in the ground, in containers, or in raised beds. I recommend amending the top 6 to 10 inches of soil with organic material because tomatoes are heavy feeders and require nutrient-rich soil.

As we move forward in our sustainable gardening practices, some familiar materials, like peat, are no longer recommended.

There are some great sustainable alternatives that are widely available. Keeping in mind that the roots will grow down as well as out, the following combination should be spread evenly across your growing area. 

25% Topsoil 

Raw topsoil is defined as an untouched substrate that has been revealed and removed during various construction projects. Compost and other organic materials are added to commercial topsoil to create ‘garden soil’.

The percentage of these added materials in off-the-shelf options is often not enough for certain plants, like tomatoes. Thus, the need to add equal amounts of other beneficial materials. 

25% Organic Compost or Manure 

Compost is a combination of natural materials, like leaves, kitchen scraps, and even black-and-white newsprint, that have been left to break down to their simplest form. Manure is an animal by-product that typically comes from farm mammals and birds. Full of slow-releasing, organic nutrients and beneficial microbes (most of which are often lacking in synthetic fertilizers), these material promote nutrient accumulation and water retention. 

25% Perlite

Perlite is a naturally occurring volcanic glass that expands when heated to a specific temperature. It feels soft, a little like packing peanuts, and is superb at improving aeration, drainage, and insulation qualities in garden soil.

This is a great alternative to peat. Vermiculite would be a good second choice. You could use a mixture of both to make up the 25% needed for adequate drainage and aeration. 

25% Coconut Coir 

Coconut coir is harvested from the inner husk of a coconut, just below the outer shell, and possesses the natural ability to retain moisture and nutrients while providing adequate oxygen to tomato roots. This effective substitute for peat also deters pests, which tomatoes are quite prone to.

Coir is also slow to decompose. So, you may not have to replace it all that often. It’s an excellent, organic additive to your soil. 

Soil pH for Tomatoes 

Like most vegetables, tomatoes thrive in soil that’s slightly acidic with a pH range of 6.0 to 6.5. Tomatoes will still grow in pH levels down to 5.8 and up to 7.0. They just won’t absorb nutrients as efficiently.

Anything above 7.0 will block access to nutrients entirely. A pH lower than 5.8 causes plants to become vulnerable to damaging heavy metals in the soil that inhibit photosynthesis. A bit of lime will increase your pH and elemental sulfur will lower it if need be. 

In the wild, these vining beauties have to fend for themselves. Because tomatoes like a little soil acidity, it makes sense that these vegetables have evolved to have their roots secrete a thin sap that actually lowers the soil pH. Keep this in mind when you’re working on getting your soil pH just right. 

Best Soil Amendments for Tomatoes 

Many commercial potting soil options include a lot of unnecessary fillers. So, be sure to read the list of ingredients prior to purchase. 

The best and most cost-efficient additives are organic and inorganic ones that you can add to basic topsoil yourself:

  • Well-aged compost
  • Manure
  • Time-release fertilizers
  • Perlite, vermiculite, coir or coarse sand

Like peat, there are a number of elements that gardeners have been adding to their soil for years that are both unsustainable and are actually harmful to your tomato plants (they end up contaminating the soil in the long term). One of them is Epsom salt. Recent studies have shown that this element blocks calcium absorption, which stunts photosynthesis and promotes blossom-end rot. 

Tomato Fertilizer 

I’ve tested quite a few tomato fertilizers and the best performers were either specifically formulated for these vegetables or had an appropriate NPK ratio relative to their needs. All-purpose feeds aren’t tailored to the needs of tomatoes. So at least a partial focus on tomatoes is crucial. 

For well-composted soil, the best NPK ratio will be 4-6-3. This will prevent overfeeding and plant damage. If you don’t compost, that’s okay. A 12-15-30 NPK ratio will balance less fertile soil just fine. 

Compost or Manure 

Compost is an effective soil conditioner with generous amounts of nutrients that won’t overwhelm plants. It also improves moisture retention and drainage in sand- or clay-based soils.

An alternative to compost is aged animal manure. This also has natural nitrogen, phosphorus, and potassium that plants thrive on.

Best Commercial Potting Mix for Tomatoes 

Whether you grow your tomatoes in the ground, in containers, or raised beds, making your own potting medium gives you far more control over soil quality and plant health. If you prefer to purchase a ready-made potting mix, it’s critical that, just like fertilizer, you choose one specially formulated for tomatoes. 

The best pre-made soil for tomatoes will consist of sterilized topsoil mixed with materials like perlite, vermiculite, and coco coir to promote adequate moisture retention and aeration. Some options will even include beneficial microbes in their formulas along with a time-release fertilizer. 

Soil In Tomato Grow Bags 

Typically made of water-proof fabric, grow bags are quite porous. This provides the roots of your tomatoes with good air circulation, which results in better water and nutrient absorption and a more robust root system. 

For this reason, a smaller proportion of additives, like perlite or vermiculite, are needed. A bit more nutrient-rich compost can be introduced to ensure that nourishment is accessible despite the higher potential for run-off. Making several small holes in the bottom of the bag, instead of just a few large ones, will help deter run-off. 

Best Soil for Tomatoes In Containers Or Pots 

When using plastic or ceramic pots or containers for growing your tomatoes, it is important to get the right balance between good drainage and air circulation versus enough material to allow for good moisture retention.

tomato in plant pot

Any potting soil that dries out on a regular basis will lead to flowers dropping prior to fruiting, tomato skins splitting, or a smaller yield overall.

A rich, loose, fibrous soil is best, including large amounts of organic materials. So a mix containing compost, coco coir, peat moss, and perlite is perfect — rich, fluffy, and well-aerated.

How To Prepare Soil for Tomatoes 

Harvesting juicy tomatoes in autumn starts with solid soil preparation in spring. Before I even think about amending my soil, I first turn the soil that’s there. Then I let it sit for a couple of days. Doing this allows the sun to eliminate any harmful bacteria that may have accumulated in your soil over the winter.

Tomatoes are heavy feeders with deep and wide-spreading roots. So, the top 6 to 10 inches of the substrate should consist of the following:

  • Quality topsoil
  • Well-aged compost
  • Organic aeration and water retention materials
  • Beneficial microbes that make nutrients available to plants

Drop handfuls of this rich mixture across your growing space. Then, spread it evenly throughout the area using a sturdy level rake.  

Best Way To Plant Tomatoes 

Choosing the right tomato variety for your space is key. Smaller ‘determinate’ types like Roma and Golden Plum typically grow to a maximum height of 2 to 4 feet. They’re perfect for pots.

Bushy types like Beefsteaks and Brandywines are indeterminate. This means there’s really no limit to how big they’ll grow. So, these need more room and perform better in the ground or in raised beds. 

Dig your planting holes 12 inches deep and place equally tall seedlings in with a handful of slow-release fertilizer. 

Fill containers (minimum 10 gallons) halfway. Snip off all lower plant leaves until the bottom third of the stalks are bare, then plant with a handful of fertilizer. Backfill the pot up to 1 ½ inches below the top. 

How Many Tomato Plants Per Square Foot?

To provide for adequate root growth and photosynthesis, one tomato plant per square foot is recommended. This also gives vining varieties plenty of room to spread out without moving in on other vegetables.

If you’re only growing small, indeterminate varieties, a bit closer would be fine. Planting any tomato variety too close, though, will result in reduced air circulation, which often leads to mold and mildew issues and disease. 

Tomato Container or Pot Size 

For indeterminates, pot size should be a minimum of 24 inches deep and 20 inches across with a 10-gallon capacity. This allows for healthy root growth and air circulation throughout the foliage. For larger, indeterminate varieties, a minimum 18-gallon capacity is needed for optimum performance. 

How Deep To Plant Tomato Plants 

A good rule of thumb for bushy varieties is to dig your hole as deep as your seedling is tall. For example, a 12-inch hole for a 12 inch tall plant. This encourages a sturdy root structure to hold up all those big, juicy tomatoes.

In pots, planting the roots and the bottom ⅓ of the stalk allows for this same benefit with extra roots growing from the stalk.  

Can I Plant Tomatoes In The Same Spot Every Year ?

Five years is the recommended maximum for planting tomatoes in the same spot. The reason is, over time, soil-borne diseases build-up that can kill tomatoes. 

However, if you’re limited to a small plot, all is not lost. Turning and tilling your soil before a long stretch of sunny days will help ‘burn off’ harmful soil bacteria. Yearly additions of compost will maintain soil fertility. 

How Much Water Do Tomato Plants Need ?

For proper hydration, tomatoes generally require 1 to 2 inches of water per week. Due to run-off and evaporation, those grown in containers will require more. In warm climates, this often means daily watering.

Signs of overwatering are easy to spot. Tomatoes begin to crack as excess water pushes out against their thin skin. Blisters or bumps may appear on the foliage. 

Verdict: Best Soil for Tomatoes 

Quality and fertility result from combining sterile topsoil with well-aged compost, materials that contribute to aeration and water retention properties, and, of course, those all-important soil microbes. This will ensure you avoid the common problem of growing small tomatoes due to the poor availability of nutrients.

Planting at the right depth and in the right-sized pot will also encourage a healthy root structure to hold up all those tomatoes.

Tomato Soil FAQs