How To Improve Soil for Tomatoes (DIY Guide)

Tomatoes are not very picky with the soil they grow in. But after everything is said and done, good tomato yields always come from good soil. Regardless of where you are growing tomatoes, there is always something you can do to improve your soil quality.

Here are six steps towards improving your soil for tomatoes:

  1. Do a soil test.
  2. Prepare the garden bed.
  3. Set the right pH.
  4. Adjust nutrient levels.
  5. Add compost to the soil.
  6. Keep the soil warm.

The rest of this article will take you through each of these steps in detail. The best part about these tricks is that anybody can apply them without the need for a professional. Let’s find out how.

1. Do a Soil Test

There is a lot of variation in soil types. When it comes to soil improvement, there isn’t a one-size fits-all approach. As a tomato farmer, most of the treatment you’ll apply on your soil depends on what kind of soil you’re working with. 

This is why you need to do a soil test. Before you prepare your soil for planting, find out what’s in it. It will save you from over fertilizing the soil or applying the wrong chemicals to it.

The easiest way to know the quality of your soil is by using a soil test kit. You can find a soil test kit at your local garden shop and some convenience stores.

Doing a soil test will help you understand important parameters about your soil. By knowing things like the acidity and nutrient levels in the soil, you’ll be able to predict how well your tomatoes will grow. It will also enable you to make necessary changes to improve your soil from an informed point of view.

A good soil test will give you two important pieces of information about your soil: the pH and the nutrients in the soil.


pH stands for “potential of hydrogen“. Without getting too much into the chemistry, this is simply a measure of the acidity of the soil. 

The pH scale runs from 0 to 14, with 7 being the neutral spot. The lower the pH, the more acidic the soil is. The higher the pH, the less acidic, or more alkaline, the soil is.

The natural pH of soil is normally a result of the natural rock from which the soil was formed. Other factors such as climate, vegetation, and time can also affect the soil pH.

Every plant has a certain level of soil pH where they grow best. Tomatoes will tolerate most soil. But generally, they prefer to grow in soil that is a bit acidic. 

A good range is at a pH between 6.2 and 6.8. Anything below or above that will not give you the best harvest from your seeds.

The soil pH is important because it affects the type of nutrients in the soil. Certain minerals are abundant in alkaline soil while others are only available in acidic soil. If you’ve had problems with the quality of your tomato yield in the past, it might be possible that the issue was with the soil pH. 

Nutrient Levels

Tomatoes, like all plants, require an adequate supply of nutrients from the soil in order to grow. Nutrients that are required in abundance are called macronutrients; those that are needed in small quantities are called micronutrients.

Soil macronutrients include:

  • Sulfur
  • Magnesium
  • Phosphorus
  • Calcium
  • Potassium
  • Nitrogen

Soil micronutrients include:

  • Boron
  • Iron
  • Copper
  • Molybdenum
  • Manganese
  • Zinc

Soil pH and nutrient level are inter-connected. Soils that are strongly acidic are not ideal for tomato growth because they have too much manganese and aluminum. They also contain low levels of calcium, magnesium, phosphorus and molybdenum. 

Soils that are overly alkaline lack zinc, manganese, boron, and copper. 

However, pH is not the only factor that determines the nutrient levels in your soil. Other determinants of soil fertility are:

  • Organic matter in the soil
  • Soil water content
  • Organisms in the soil 
  • Soil texture
  • Fertilizers in the soil

So how do you test for the pH and nutrient level of your soil? There are two ways: 

  • Use a commercial soil testing kit
  • Use a professional soil testing lab

How To Test Soil With a Commercial Soil Testing Kit

Commercial soil testing kits are affordable and accessible. They will give you a general overview of the pH and the amount of sodium, phosphorus and potassium in your soil sample. This Luster Leaf Soil Test Kit (available on provides good and effective results in 8 easy steps:

  1. Get a clean plastic container that you will use to collect the soil samples. Before inserting any soil samples, clean the container with clean water and make sure it’s dry before you proceed.
  2. Get rid of any weeds, debris, organic matter, and other objects from the surface of the soil from which you’re getting the sample. This will help you get a more pure sample of the soil.
  3. Map out the area where your soil samples are going to be collected. Planning ahead will ensure that you sample the right area according to where you will be planting.
  4. Collect your first soil sample by digging a 4 to 6 inch (10.16 to 15.24 cm) hole into the ground. Take note of the spot on your map.
  5. Move onto the next spot and collect another sample. Each sample should be about the same size.
  6. Do the same for about 5 to 10 areas of your sampling space. Ensure that you are not collecting from an area that was recently treated with fertilizer or pesticide.
  7. Mix all the collected samples using a trowel. Make sure that you mix thoroughly.
  8. Following instructions on the test kit, conduct your soil test. Each kit will have slightly different directions depending on the particulars of the methods used.

How To Test Soil Through a Commercial Soil Testing Lab

Commercial soil testing labs use numerous techniques and equipment to test a soil sample. They will typically generate a comprehensive report that includes the macro and micronutrients, soil texture, and pH of your soil sample. 

If you feel like you need a detailed report about what’s in your soil, contact a soil testing lab near you. All you have to do is ask about their services, and send your soil sample in a prepaid mailer. Test results usually come back after a couple of weeks.

Soil Texture

Soil texture refers to whether the soil is loam, sandy or clay. Soil has plenty of minerals that come from different particles in it. Soil texture is determined by the amount of sand, silt and clay particles that make up the minerals in the soil.

Heavy soils typically have a high amount of clay, while light soils usually have a greater percentage of san particles. The texture of soil has many implications, and it can affect:

  • The water content in the soil.
  • The rate at which water moves through the soil.
  • The fertility of the soil.
  • The aeration of the soil.

Tomatoes can grow in most types of soil, except soil that is predominantly clay. They also don’t live well in mushy waterlogged soil. The ideal texture of soil that tomatoes need is that between loam and sandy.

2. Prepare the Garden Bed

By now, your soil test results might have given you an insight into the type of soil you’re working with. But before you can make any treatments on the soil, you have to prepare it first. Here are some of the things you must do at this stage:

Eliminate Volunteer Crops

If you’ve been using your land for growing tomatoes or other vegetables in the past, you might see a few volunteer crops. These are plants that you did not intentionally plant but for some reason happen to be there in the garden. 

Volunteer crops come from seeds that dropped from the previous group of plants that were growing in the garden. In normal cases, these are fine to leave in the garden. 

However, volunteer crops might crowd your next batch of plants if they’re left in the garden. Even more importantly, they could be infected with disease that could spread to the new, healthy plants.

Remove Debris From the Soil

Get rid of any rocks, sticks, or plant roots in the soil. You can do this by using a garden rake for the smaller objects. For large boulders, you may handpick them out of the dirt. 

In addition, remove any weeds and unwanted plants growing in the garden plot. Be sure to pull them out completely from the roots so they do not grow back. When most of the unwanted material has been removed, rake the soil and level it.

Break Up Chunks of Soil

If you have any clods of soil in the garden, break them up using your hands or a hoe. If they are left there, they can make it hard for the roots to penetrate the soil for nutrients. You might want to hose the harder masses of soil with water to ease the process of breaking them up.

Create an Edge on the Garden Bed

If you’ve removed weeds from your planting bed, the last thing you want is from them to come back. You can stop grass from creeping back into the garden by creating some edging around the garden. 

You can use large stones to neatly create boundaries on where you are going to plant the tomatoes. Be sure to sink them fairly deep into the soil to prevent any weeds from growing underneath them.

3. Set the Right pH

If your soil is not at the right pH, there are a few things you can do to adjust it. Remember that we’re looking for a pH between 6.2 and 6.8. 

How To Increase pH

The commonest way to reduce soil acidity is by using agricultural limestone. You should essentially apply the limestone two to three months before planting to give it enough time to react with the soil. 

It can be finely ground, granular, pelletized or hydrated limestone.The rule of thumb is that the finer the limestone, the more easily it changes the soil’s pH. 

There are also other factors that affect how fast limestone interacts with soil to change its pH. These include:

  • Texture of the soil
  • Moisture in the soil
  • Organic content in the soil

The table below shows the average tons of finely ground limestone per acre required to increase soil pH.

Soil texturepH Increase from 4.5 – 5.5pH increase from 5.5 to 6.5
Sand and loamy sand0.50.6
Sandy loam0.81.3
Silt loam1.52.0
Clay loam1.92.3

Alternatively, you may use wood ashes to raise your soil pH. Wood ashes contain calcium, magnesium and trace amounts of phosphate and boron. The downside to wood ashes is that they take very long to create change in pH.

How To Lower pH

In some cases, the pH of your soil could be higher than necessary. To adjust the pH level, you’ll need to make the soil more acidic. Aluminum sulfate and sulfur are two common agents that can effectively lower soil pH.

Sulfur takes much longer to make the soil more acidic because it needs to react with bacteria in the soil. The speed of its reaction with soil depends a lot on the amount of bacteria in the soil, the temperature of the soil, moisture in the soil, and fineness of the sulfur. 

If the conditions of the soil are not ideal for the reaction to occur, the change in pH can take several weeks or months to occur.

On the other hand, aluminum sulfate instantly reacts with the soil to lower its pH.

The table below shows the amount of sulfur per acre required to lower pH to 6.5.

Original pHSandy soilClay soil
8.50.7 – 1.01.0 – 1.3
8.00.5 – 0.70.7 – 1.1
7.50.2 – 0.30.4 – 0.5

4. Adjust Nutrient Levels

After optimizing the pH of your soil, your tomatoes stand a good chance of thriving. However, you can make your yield much bountiful by enriching your soil with nutrients. There are particular minerals that tomatoes and other plants require to stay healthy as they grow.

Essentially, your tomatoes need a certain ratio of nitrogen (N), phosphorus (P) and potassium (K) to produce healthy yields. The ideal NPK combination for tomatoes should be low in nitrogen, high in phosphorus and medium or high in potassium. 

If your soil test results showed that the soil nutrient levels are fairly even but low in quantity, simply buy an NPK fertilizer to fix the deficiency. These fertilizers come in different ratios of nutrients, depending on the customers’ needs. 

For tomatoes, you might want to get a 8-32-16 or 6-24-24 fertilizer. The numbers simply represent the ratio of concentration of the nutrients. For example, 8-32-16 means for every 8 units of Nitrogen, there are 32 units of Phosphorus, and 16 units of Potassium. As you mix in fertilizer, keep it within 6 inches (15.24 cm) above the soil.

If your soil test result indicates a particularly low nutrient, then you need to focus on elevating that one. You can do this by getting a fertilizer that is particularly concentrated in the lacking nutrient. There are also other remedies that can improve individual nutrients in your soil.


Nitrogen is important for tomatoes to produce fruit with the help of the sun’s rays. It helps the leaves to produce chlorophyll, which is used in photosynthesis and overall plant growth. When it is abundant, your tomatoes will bloom in time. 

Blood meal is a rich source of nitrogen for your soil. It is simply dried animal blood that you can find at butcher shops. Add it to your soil and water it in to boost the nitrogen levels. Keep in mind that it might attract critters to your garden. Alfalfa meal is a great alternative source of nitrogen. 

Other sources of nitrogen include animal manure and nitrogen fertilizer.


Phosphorus is an essential component that helps your tomatoes fight diseases, grow fruit and build strong roots. Phosphorus also helps the plant in developing complex proteins that are responsible for growing new tomatoes. 

If your tomatoes have red stems and leaves, this could be a sign that they lack phosphorus. You’ll notice an odd dark-green color in their leaves if they do not have enough phosphorus.

Bone meal is a great natural source of phosphorus. You may also add phosphorus to your soil by mixing in a phosphorus-rich fertilizer like 10-20-10 NPK.

Rock phosphate is another effective source of phosphorus. This Espoma RP28 Rock Phosphate (available on is easy to apply and will instantly boost the amount of phosphorus in your soil.


Potassium helps promote growth and disease resistance in your tomato plants. Although the signs of potassium deficiency are not easy to identify, yellowing of leaves might mean that your tomatoes need more of the mineral. Weak plants and slow growth may also indicate a potassium deficiency.

Add wood ash or granite dust to increase potassium in the soil. Adding seaweed will also naturally raise your soil potassium levels. You may also opt for a fertilizer with an abundance of potassium.

You may also increase potassium levels in the soil by growing potassium bio-accumulators together with your tomatoes. Bio-accumulators are plants that naturally mine the soil for potassium and bring it closer to the surface. 

Examples of bio-accumulators are yarrow and horsetail. Try to prune these plants throughout the season and use their parts as mulch. As the mulch degrades, it will also act as an organic source of nutrients for your tomatoes.

5. Add Compost to the Soil

You can improve the fertility of your soil by adding compost to it. Compost slowly releases nutrients while maintaining moisture in the soil. In addition, the compost will increase the durability of any fertilizer you might have added to the soil.

Good compost should be dry and free from odor. If the compost is not mature enough, it will still retain the rotting smell of the original components. If it is used in this state, it can attract pests that can be harmful to the seedlings.

Balance your compost with green and brown materials. Green materials are a source of nitrogen and protein which supports the growth of microbes that break down the heap. 

Examples of green materials include:

  • Coffee husks
  • Teabags
  • Fruit and vegetable remains
  • Plant trimmings
  • Lawn trimmings
  • Eggshells
  • Animal manure
  • Seaweed

It’s important to stay away from dog and cat manure. It usually contains parasites that can lay eggs on your tomatoes. If the eggs are eaten, they could be dangerous to your health. 

Brown materials not only feed the microorganisms in the compost but also bulk up the pile. 

The browns include:

  • Fall leaves
  • Hay
  • Small branches and twigs
  • Sawdust
  • Maize stalks

Have a ratio of 3:1 of browns to greens for an ideal tomato compost. Mixing an inch of compost and mixing it with the top layer of the soil should do the trick. 

Remember that your compost heap needs to heat up in order for it to break down. If this doesn’t happen you might start to experience a bad smell coming from the compost. At this point , you can speed up the breakdown by adding more green material. 

6. Keep the Soil Warm

Once the soil is treated, it’s time to get it warmed up for planting. Tomatoes grow fast in warm soil. It preserves organic nutrients and helps the seedling in the early stages of its root growth.

Keep the soil warm by applying a black plastic sheet over. It will lock in moisture while preventing weeds from sprouting. Plastic is okay to use provided you don’t leave it in the soil at the end of the planting season. 

If you are skeptical about using plastic, you may use black biodegradable plastic mulch (BDM). BDMs can safely remain in the soil when it’s time to till the bed. Over a period of about two years, they are broken down by microorganisms in the soil. 

It’s important that the film of mulch be black because the color easily absorbs and retains heat from the sun. Apply the sheet onto the soil and leave it for about three weeks. You can either take it off before planting the tomatoes or cut holes in it where the tomatoes will grow. 


Tomatoes are fairly easy to grow if you give them the right soil. You can put your soil in top condition by doing the following things:

  • Run a soil test to know your soil well.
  • Get your garden bed in planting condition.
  • Get your soil into the pH range that favors tomato growth.
  • Add compost and fertilizer to boost the soil nutrients.
  • Do some mulching to keep the soil nice and warm.

Alexander Picot

Alexander Picot is the principal creator of, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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