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How to Make Your Own Potting Mix for Growing Tomatoes

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It may surprise you to learn you can make your own potting mix for growing tomatoes for less money than the cost of buying a commercial potting mix …

… and your homemade potting mix can be better for your tomato plants than what you buy at the home improvement store.

Plus, you can put together your potting mix any time of year even before planting season, while you’re waiting for spring to come.

The Difference between Seed Starting Mix and Potting Mix for Tomatoes

Potting mix and seed starting mix have slightly different ingredients. That’s because they have different tasks.

The job of a seed starting mix is to give your tomato seeds a safe environment so they can sprout, develop their first couple of sets of leaves, and remain disease-free. The seed itself provides the initial food for the plant, so seed starting mix need little (if any) fertilizer to do its job.

Put simply, the best seed starting mix is sterile and has little fertilizer.

Potting mix for tomatoes, on the other hand, has a different function. It will become the permanent home to your tomato plants while they are in containers or pots. That means the mix needs to provide both a good home plus food.

The best potting mix for tomatoes may or may not be sterile, yet it must contain nutrients in order to grow healthy plants.

Why Make Your Own Potting Mix for Tomatoes?

How to Make Your Own Potting Mix by Tomato Dirt

You save money

Commercial potting mixes are more expensive to buy than the ingredients you need to make your own potting mix.

You create a better growing environment

Many pre-packaged potting mix formulas have too much garden loam or peat moss. These ingredients compact in containers, producing a heavy, hard texture which makes aeration and drainage difficult. To compensate, mixes include chemical wetting agents, which are not really necessary if you have a balanced mixture in the first place. Some commercial mixes have other ingredients, too, like excess pine bark, which gives the mix a high-acid pH and consumes extra nitrogen. That deficiency must be replaced by fertilizer in order for your tomatoes to thrive.

(Check out these tips to use if you decide to buy commercial potting mix for growing your tomatoes.)

Ingredients to Use to Make Your Own Potting Mix

Potting mix needs to

  • drain well
  • aerate well
  • retain well
  • nourish well

A good potting mix is a blend of  ingredients that fulfill those functions. A combination of both inorganic and organic ingredients to meet tomatoes’ needs for growing healthy leaves, blossoms, and fruit.

Inorganic Ingredients Drain and Aerate. Inorganic ingredients like sphagnum peat moss, peat coir, perlite, vermiculite, and coarse sand give the mix good drainage for water and allow pockets for air to move.

Organic Ingredients Retain and Nourish. Organic ingredients like compost, humus, garden loam, and commercial potting mix play two important roles. First, they offer water retention, helping the mix hold water rather than repel it in order to keep the plant hydrated and keep nutrients moving to the leaves. Further, these organic ingredients provide nutrients for your tomato plant to grow healthy and strong.

(Click here to find inexpensive sources for potting mix ingredients.)

Basic Homemade Potting Mix Recipe

There are dozens of recipes to use to make your own potting mix. Here is an easy one: 1 – 1 – 1. (We at Tomato Dirt use this recipe.)

  • 1 part inorganic material for bulk (peat moss or coir)
  • 1 part inorganic material for good drainage (perlite, vermiculite, or coarse sand - or a combination of these)
  • 1 part organic material for water retention and nutrients (compost, humus, garden loam, or commercial potting mix)

Experiment with these specific ingredients to find a good combination that works for you.

How to Make Your Own Potting Mix  

  1. Gather ingredients, a large tub (or wheelbarrow) for mixing, trowel or shovel, and gloves.
  2. In a large bucket or tub, pre-soak sphagnum peat moss or peat coir in warm water, in a two-to-one ratio (2 parts product to 1 part water), until water is absorbed.
  3. Add other inorganic ingredients to the peat mixture. Combine together.
  4. Add organic ingredients.
  5. If using the potting mix right away, then add the appropriate amount of time-release fertilizer for pot size (as indicated in fertilizer instructions.) If saving the potting mix to use later, then store it.
  6. Fill your containers

Should You Sterilize the Organic Ingredients in Your Mix?

It's your call.

If garden loam or garden compost are ingredients in your mix, you may wish to sterilize them in order to eradicate bacteria and fungus that have overwintered in the soil.

To sterilize, heat your oven to 180º - 210º F. Spread the ingredients in a shallow pan. Bake the soil for 45 minutes. Allow it to cool and then add it to your mixture.

Extra Tips for Making Potting Mix

  • Make potting mix ahead of time – before planting season. Store it until you need it. This saves time in the spring when you’d rather be outside working in the garden … plus it gives you a “gardening task” to do in late winter when you’re itching to play in the dirt.
  • Wear a dust mask when adding ingredients together and mixing so you don’t inhale particles, especially if you use perlite or vermiculite.
  • Combine ingredients in a large flexible bucket or plastic container – one with handles – to make it easy to mix and to make it easy to carry out to the garden or patio where you will transplant tomatoes.
  • Store extra potting mix in a plastic trashcan with a lid or a sealed plastic container.
  • Add time-release fertilizer to your mix when you plant tomatoes in order to grow healthy and strong throughout the season.

More about Potting Mix and Seed Starting Mix

Potting Mix vs Potting Soil: Which Should You Use?

What potting mix should you use for growing tomatoes in pots?

What potting mix to use when starting tomatoes from seeds ...

Sterile potting mixes: do you need them for growing tomatoes?

Review: Pro-Mix Seed Starting Formula for growing tomato seeds ...

Review: Coco Coir as a Potting Medium for Tomatoes ...

Seed starting mix for tomatoes: what ingredients are important ...

More Tomato Seedling tips on our Pinterest board ...

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