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, red jewel of a tomato, right off the vine, and taking that first juicy bite. Now, the centerpiece of every vegetable garden, the simple yet sensory pleasure of the tomato was first discovered and cultivated by the South American Aztecs. In the 1500s, explorers caught on and brought these colorful gems back to European pallets.

Their original yellow and orange coloration evolved, through selective breeding, into the more familiar red. Fortunately, ‘heirloom’ seeds from those originals were collected and preserved. Then, used to develop those same sunset hues into a wide variety of contemporary varieties. Everything from Beefsteaks to Romas to Cherry tomatoes can be found in red, orange, yellow, and even purple. Many with interesting variegated patterns.  

Reaching that stage of juicy ripeness, in any variety, means that specific tomato plant requirements have been carefully adhered to. Each stage of a tomato plant’s growth requires slightly different care, in order for it to be healthy and fully productive. This process starts from the ground up, literally. And where better place to start than with cultivating the best soil for tomatoes? 

Best Soil for Growing Tomatoes 

Studies have shown that, like a fine wine, a well-developed flavor profile greatly depends on the composition of the soil. Weather plays a part too. But, for optimum flavor and overall performance, the soil needs to be well prepared. 

Now, tomatoes will grow in just about any kind of soil, except clay. The roots simply can’t push their way through it. But, the extent of 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 between 5.8 and 7.0. Contrary to common practices, it has also been found that adding sand or peat will not enhance flavor or soil fertility. Filling the top 6 -10 inches of the substrate with organic compost, quality topsoil, and other beneficial additives will create the best soil for your tomatoes. I recommend purchasing a soil test kit to check the pH, or even sending a sample off for a lab test.

tomato in greenhouse

Greenhouse Vs Containers 

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

The environment that a greenhouse offers is a little different. Clear panels intensify natural sunlight and warmth, which promotes increased photosynthesis and vigorous growth. And fans can cool things down on a hot day. 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 filling the top 6-10 inches of the substrate with fertile content 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. In commercial topsoil, compost and other organic materials are added to create ‘garden soil’, which is more suited to house the roots of healthy plants.

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 also promote nutrients and water retention. Especially when combined with the following ingredients. 

25% Perlite for Drainage 

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, even in heavy, clay soil. Making this a great alternative to peat. Vermiculite would be a good second choice. Although you could use both to make up the 25% needed for adequate drainage and aeration. 

25% Coco Coir 

Coco 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. Making it an excellent, organic additive to your soil. 

Soil pH Level for Tomatoes 

Like most vegetables, tomatoes thrive in soil that’s slightly acidic, which would be around the 6.0 – 6.5 pH range. They’ll still grow 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. Lower than 5.8 and plants will become vulnerable to the effects of 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 secret a thin sap that actually lowers the soil pH. Thereby raising its acidity. Keep this in mind when you’re working on getting your pH just right. 

Best Soil Amendments for Tomatoes 

Many commercial potting soil options include a lot of unnecessary fillers that upset the pH balance of your soil and commandeer nutrients. Leaving your plants hungry. 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 – To attract beneficial soil life
  • Time-Release fertilizers
  • Perlite, vermiculite, coir or coarse sand – for moisture retention and aeration

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 rot in an array of tomato varieties. 

Tomato Fertilizer 

I’ve tested quite a few tomato fertilizers and the best performers were either specifically formulated for them or had an inclusive NPK relative to their needs. All-purpose feeds aren’t balanced enough. At least a partial focus on tomatoes is crucial. 

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

Compost or Manure 

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

An alternative to compost is the use of animal manure. This also has natural nitrogen, phosphorus, and potassium content that plants thrive on. However, do your research before using any fresh manure. Some are too strong when fresh and need to be aged before use. 

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. But, if you prefer to purchase a ready-made potting mix, it’s critical that, just like fertilizer, you choose one specially formulated for tomatoes. 

As previously mentioned, some commercial potting soils include a lot of unnecessary fillers. So, read the label. Just as you would at the grocery store. 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. Allowing the roots of your tomatoes 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 to encourage this. 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 post or containers for growing your tomatoes, it is important to get the right balance between allowing good drainage, and therefore air circulation around roots, versus enough material to allow for good moisture retention to prevent the soil from drying.

tomato in plant pot

Any potting soil that dries out on a regular basis will lead to flowers dropping prior to fruiting, or tomato skins splitting, or the plant becoming prone to producing a small yield.

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 start 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 6-10 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 2-4 feet. 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. 

Here, dig your planting holes 12” 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” 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” deep and 20” 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” deep hole for a 12” 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 

5 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. And yearly additions of compost will maintain soil fertility. 

How Much Water Do Tomato Plants Need 

For proper hydration, tomatoes generally require 1-2 inches of water per week. Due to run-off and evaporation, those grown in containers will require more. In warm climates, this means daily watering. Sometimes twice, in mid-summer. But, no more than that. 

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

Verdict: Best Soil for Tomatoes 

So, what’s your verdict? Will you be growing smaller, determinate tomatoes or bushier, vining ones? Will you grow them in pots, raised beds, or in the ground? No matter what your fancy, they all succeed and provide you with an abundance of juicy fruit when you start by cultivating the right soil. 

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. 

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

Best Soil for Tomatoes FAQ’s