The Best Soil pH for Tomatoes and 7 Facts About It

Updated April 1, 2025

Tomatoes are one of my favorite crops to grow and the one I’ve grown the longest. They’re an easy crop to start out with and a garden favorite to many. Whether you’re planting in a small garden, raised beds, or large-scale plots, understanding the best soil pH for tomatoes is essential for healthy plant growth and a bountiful harvest.

Soil pH directly affects nutrient availability, plant development, and disease resistance, influencing everything from fruit clusters to overall yield. Let’s dive into the ideal pH range for tomatoes and the best way to manage soil acidity for thriving plants.

This post is all about the best soil pH for tomatoes.

Table of Contents

What is Soil pH and Why Does it Matter?

Before diving into soil pH for tomatoes, let’s review the basics about soil pH. pH stands for ‘potential hydrogen’ and is an indication of soil reactivity. Soil pH refers to the acidity or alkalinity of the soil, measured on a scale from 0 to 14. A pH of 7 is neutral, while anything below 7 is considered acid soil, and anything above is alkaline soil. The pH of soil impacts the absorption of essential nutrients, soil moisture retention, and the overall plant growth process.

For tomatoes, a slightly acidic soil with a pH range of 6.0 to 6.8 is ideal. This range ensures the availability of essential nutrients like nitrogen, phosphorus, and potassium, all of which contribute to strong plant growth, disease resistance, and high fruit production. Incorrect soil pH can result in diseases such as blossom end rot in tomatoes. Blossom end rot can be caused by a number of factors including excessive nitrogen, calcium deficiency, and soil that’s too acidic (low pH). Soil that’s too acidic causes calcium to be less available to the plant, causing malabsorption.

When to Plant Tomatoes

The best planting time for tomatoes depends on soil temperature and the danger of frost. Young plants and tomato seedlings should be planted in early spring once the soil temperature reaches at least 60°F. If you start your tomato seeds indoors, using peat pots can give you a head start before transplanting them into the garden when the danger of frost has passed. If planting late spring or early summer, ensure that the plants receive an inch of water per week through heavy soakings rather than frequent light watering.

How to Test Your Soil pH

Before making any amendments, testing your soil is a good idea. The first step in determining the soil pH value is using soil test kits or sending a soil sample to a local agricultural extension for a soil test report. If you lack a test kit, observing signs like yellowing lower leaves or nutrient deficiencies can indicate pH imbalances.

As a general rule of thumb, it’s important to not overdo it with soil amendments. Putting too much of any one good thing can have the opposite intended affect, such as burning plants with too much fertilizer. A good soil test kit will tell you exactly what to add to your soil for the appropriate amendments.

Can Soil Be Too Acidic or Too Alkaline for Tomatoes?

A short answer to this question is yes! As a longer answer, while tomatoes prefer slightly acidic soil, extremely low pH can lead to nutrient deficiencies and common problems like blossom-end rot and stunted plant development. On the other hand, soil that is too alkaline (high pH) can reduce the availability of essential nutrients, leading to issues like early blight, verticillium wilt, and fusarium wilt.

How to Adjust Soil pH for Tomatoes

Raising Soil pH (Reducing Acidity)

If your soil test report shows that the soil is too acidic (below pH 6.0), you can raise the pH by incorporating the following amendments:

Garden Lime: One of the best ways to increase pH naturally. It’s one of my favorite additions to use for soil amendments. It’s something I’ve used since I began gardening and it’s an easy application. I buy a bag of the pulverized garden lime, which is a very fine, white powder.
Wood Ash: Contains essential nutrients but should be used cautiously, especially if sourced from fireplaces or kitchens. It’s composed of up to 20%+ calcium, potassium (or potash), magnesium, phosphorus, and sulfur. There are also trace amounts of boron, iron, aluminum, manganese, zinc, and more.

*** Be careful using wood ash. If you use Duraflames, don’t use the wood ash from your fireplace. Duraflame logs are prefabricated and contain lots of chemicals.

Bone Meal: It’s a fertilizer that’s made from steamed animal bones. It’s not the best smelling product but it’s an organic way to help the soil pH. It adds calcium into the soil and over time raises the pH.
Compost: Improves nutrient availability and overall soil health. It’s a great resource in the garden. The nutrients it contains lack acidity and thus won’t increase the soil pH.

Lowering Soil pH (Increasing Acidity)

If the pH of soil is too high (above 6.8), you can make it more acidic by adding:

Sulfur: Works well but takes a long time to lower pH, so apply it the year before planting.
Iron Sulfate: A fast-acting amendment that also treats iron deficiencies. It requires a large volume to lower the soil pH. Check your soil analysis before you start adding in iron. Iron sulfate is used to treat iron deficiencies, and provides quicker results in comparison to sulfur.
Sphagnum Peat Moss: Adds organic matter and helps maintain a slightly acidic soil environment. This amendment requires a large amount added to the soil as well. Adding it to the soil only slightly affects the acidity, but it adds more organic material. Add in the peat moss will help lower the soil pH for 2 years.
Acid Fertilizers: Organic fertilizers like Burpee Organic Tomato & Vegetable Granular Plant Food release nutrients slowly over time. This Burpee product is organic and it releases over a 3 month period.
Ammonium sulfate is used around the base of plants to increase the amount of sulfur in the soil. Pay close attention to how much is used since ammonium can burn plants.
Compost is always a great option in the garden. Check out my other posts on compost to help you choose the right one.

[RELATED POST: 5 Ideas on Where to Buy Compost]

[RELATED POST: The 5 Best Composts for the Garden]

What NOT to Use

Aluminum sulfate is another amendment that is popular. There are recent concerns about the use of aluminum in the garden. Not only can it be hazardous to our health, but it contaminates drinking water and groundwater. I’ve included this in the list since it can help with soil, but including this warning to steer clear of it.

Additional Tips for Healthy Tomato Plants

Use Well-Drained Soil: Heavy clay soils retain too much moisture, leading to root rot. Light sandy soils drain too quickly and require frequent watering.
Consistent waterings: It’s important that tomatoes get consistent waterings, especially when it’s super hot outside. Be sure to water plant more frequently when it’s hotter outside as the soil quickly dries. Inconsistent waterings can affect the tomato plant’s ability to uptake nutrients from the soil.
Appropriate Spacing: Give each plant enough square feet to grow properly, ensuring easy access for maintenance.
Tomato Cages for Support: Help prevent main stems from breaking under the weight of fruit clusters.
Side Dressing with Compost: Adds extra nutrients throughout the growing season.
Shallow Cultivation: Avoid disturbing the root system while weeding.

Final Thoughts

Growing tomatoes successfully starts with good soil. Ensuring the ideal pH range of 6.0 to 6.8 will lead to healthier plants, fewer disease issues like tobacco mosaic virus and septoria leaf spot, and an abundant harvest of fresh tomatoes. Whether you’re growing cherry tomatoes, sauce tomatoes, or a variety of tomato types, proper soil preparation is key to a productive season.

This post was all about the best soil pH for tomatoes and how to optimize it for a bountiful harvest. Happy gardening!

This post was all about the best soil pH for tomatoes.