Achieving the Perfect Soil pH for Tomatoes

If the soil is too acidic or alkaline, it can inhibit certain plants from taking up the nutrients that they need to survive and thrive.

If you enjoy growing tomatoes as much as I do, you’ll know that they need a sunny spot in the garden and well-drained soil that is rich in organic matter.

But, have you ever wondered what the perfect soil pH is for tomatoes and how you can achieve this?

For first-time growers or those who want to perfect their tomato growing environment, I’m going to explain what soil pH tomatoes prefer and how to achieve it.

What soil pH do tomatoes prefer?

As tomatoes are a naturally acid-type fruit, the plants prefer a slightly acidic to neutral soil in the pH range of around 6.5 to 6.7.

Why is the soil pH important, I hear you ask? While I could go into a thoroughly scientific explanation on this, let me keep it simple. 

If the soil is too acidic or alkaline, it can inhibit certain plants from taking up the nutrients that they need to survive and thrive.

harvesting tomatoes 4 | Fruit & Vegetables

In the case of tomatoes, they need a decent amount of calcium to avoid the development of the dreaded blossom end rot disease. This is primarily a sign of calcium deficiency in tomatoes.

This is reason enough to ensure that you give your tomato plants the best soil environment that you can provide.

How do you check the soil pH?

Checking the pH level of your soil is quite easy.

The cheapest place to purchase a soil testing kit is usually online from somewhere like Amazon. However, you can also get them from any garden centre, nursery or even places like Bunnings or Mitre 10.

These kits are relatively easy to use and come with full instructions on what you need to do. Make sure that you take soil samples from just below the surface.

soil sample | Fruit & Vegetables

Another device that you can use is an electronic pH meter. These have a probe attached, much like a moisture meter, that you insert into the soil to get a digital reading.

Alternatively, you can take a sample of your soil and send it off to a laboratory to get tested. This will often give you the most accurate pH reading of your soil.

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How to adjust the pH level of your soil

Once you know the pH level of your soil, it’s time to make some amendments if your soil is either too acidic or too alkaline to grow the perfect tomatoes.

garden tomatoes | Fruit & Vegetables

If your soil does need to be amended, you want to do this a couple of months before you’re ready to plant. This is because any amendments that you make to the soil will take a little while to actually affect the pH level adequately.

How to amend acidic soil

If your soil pH is below the level that is perfect for tomatoes (less than 6.5), then you need to raise the pH to get to the perfect level.

This can be achieved by adding lime to the soil. Dolomite lime is a common additive for soil to raise the pH level. This is of particular benefit for tomatoes because it also contains lots of calcium. 

With highly acidic soil, important nutrients are much more water-soluble and can easily be washed out of the soil when it rains. This is particularly the case when it comes to nutrients such as calcium, magnesium, potassium and copper.

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How to amend alkaline soil

If your soil pH is greater than the recommended 6.7, then it is going to be alkaline. Alkaline soils are usually low in important nutrients such as iron, phosphorus and manganese. 

Lowering the pH of your soil is fairly easy but will still take time to come into effect. All you have to do is add plenty of compost or other organic matter to the soil.

Compost Bin 1 | Fruit & Vegetables

It’s widely recommended that you don’t use poultry manure to lower the pH. This is because chicken manure has a pH range of between 6.5 to 8. This puts it into the more alkaline range.

While some experts recommend using other types of manure to lower the pH, there is not really conclusive evidence that this actually works effectively. This is because different manures can have different pH levels depending on what the animals are being fed.

Similarly, mushroom compost should also be avoided as it has a pH range of between 6.5 and 8. Therefore, it’s likely to raise rather than lower the pH of the soil.

If your soil is particularly alkaline, you can purchase a powdered sulphur to add to it and this should solve the problem over time. 

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Annette Hird

Annette Hird is a gardening expert with many years of experience in a range of gardening related positions. She has an Associate Diploma of Applied Science in Horticulture and has worked in a variety of production nurseries, primarily as a propagator. She has also been responsible for a large homestead garden that included lawn care, fruit trees, roses and many other ornamental plants. More recently, Annette has concentrated on improving the garden landscape of the homes that she has lived in and focused a lot of energy on growing edible plants as well. She now enjoys sharing her experience and knowledge with others by writing articles about all facets of gardening and growing plants.


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