I start thousands of tomato and vegetable seeds each year at HeathGlen Organic Farm for the St. Paul Farmers’ Market, using a homemade organic potting mix. But that approach isn’t practical for everyone. If you’re growing a few vegetables for your backyard or a balcony container garden, commercial potting soil may be the better choice.
This guide covers both options, plus the critical steps to prevent damping-off disease, which kills more seedlings than any other problem I see with new gardeners.
Quick Summary: Homemade potting soil gives you full control over ingredients but requires space and bulk materials. Commercial potting soil is convenient and consistent. Either way, use sterile mix, avoid overwatering, and keep lights close to prevent damping-off. Read time: 7 min | Experience level: Beginner to intermediate
Jump to: Homemade Potting Soils | Commercial Potting Soils | Damping-Off Disease | FAQ
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When Should You Make Your Own Potting Soil?
If you are a 100% organic grower, you can make your own potting mix (but it is a bit involved). I have tried several recipes, and my favorite combination for organic homemade potting mix is listed below.
I grow thousands of seedlings for the farmers markets, so you will need to scale down proportionally for smaller batches.
I purchased the individual ingredients for my mixture from a local feed store. I’ve included another homemade potting soil mixture below with ingredients that may be easier for you to find.
Homemade Potting Soil Recipes
My Own Homemade Organic Potting Soil
- 5 gallons compost
- 5 gallons peat
- 3 – 5 gallons mix of vermiculite & perlite
- 1/2 cup lime (don’t use this if your compost is horse manure as the beds are often limed)
- 1/2 cup bonemeal
- 1/2 cup bloodmeal
- 1/2 cup greensand (or 1/4 cup sul-po-mag)
Typical Homemade Potting Soil:
- 1 part sterilized bagged potting soil
- 1 part peat moss or coir fiber
- 1 part perlite or vermiculite
- 1 part compost
Directions for either mixture:
Moisten all ingredients and mix together thoroughly in a large clean tub. Feel the texture and if it feels heavy and sticky, add a little more peat moss. If it feels too light, add more compost.
I have also written a detailed article on starting your own tomato and pepper seeds indoors, if you want a comprehensive read on all things seed starting.
What to Look for in Commercial Potting Soil
If you are starting a container garden with large pots, purchasing bagged products might be a better option for you. It takes a lot of space to mix up bulk potting soil and it can be very heavy to cart upstairs to a balcony garden.
The best thing to do if purchasing commercial potting soil is to become familiar with the labels. Make sure it is labeled as a potting soil and not a garden mic, topsoil, or straight compost.
Ingredients to look for in a good commercial potting soil would include:
- compost
- perlite or vermiculite
- sphagnum peat moss
It is your decision whether to look for water-holding granules and time-release fertilizers. Some people prefer to add fertilizers and control the moisture content themselves.
When I don’t have the time to make my own potting soil mixture, I have found that Miracle-Gro Moisture Control is a potting soil that gives consistently good results for both seed starting and growing in containers.
Tip: The bag of soil should be light, as heavy bags may have too much sand or they could be saturated with water.
How to Prevent Damping-Off Disease
If you have ever started your plants indoors from seed, you have probably experienced a common problem called damping-off. This is when seedlings that are only a few days old suddenly shrivel and die, or just fall over.
If you take a close look at the seedlings you will usually see that the roots have rotted, or a dark spot of rot has developed on the main stem.
The culprit behind damping-off is fungi that may appear if you are using garden soil for your potting soil. Soil that comes straight from your garden often carries disease-promoting fungi that is hard on young seedlings, but doesn’t necessarily harm older plants or plants sowed directly in the garden.
Damping-off is caused by different fungi, and it is most often fatal, but the good news is that it is entirely preventable. Here are the steps I have found useful in preventing damping-off:
- Make sure your seed starting containers are thoroughly clean, especially if you are reusing containers from the year before.
- Use a sterile potting soil that contains vermiculite and peat moss. Do not use regular garden soil.
- Start with small containers (I use very small plug trays that have 128 plugs per tray and then pot up to 4″ pots when the seedlings have several sets of leaves.
- Go easy on the watering. If you can, water from the bottom. I water from the top, but with very minimal amount of water, pretty much just a dribble actually. Check the bottom tray to see if the water has seeped through to the tray. If so, you have watered too deeply.
- Keep grow lights close to the seedlings, only 1-3 inches away.
- Have a fan blowing across the tops of the seedlings to help their stems become sturdy. You may have heard about “tickling your seedlings” with your hands. Tickling the seedlings and a gentle fan on them has the same effect.
Now….give seed starting a try. You can grow so many more exciting varieties when you start plants from seed. Plus, it’s a great sense of accomplishment to watch something grow from beginning to end!
FAQ
Potting soil is lighter, sterile, and formulated for containers with good drainage. Garden soil is denser, may carry disease organisms, and doesn’t drain well in pots.
Can I use soil from my garden to start seeds? Not recommended. Garden soil often carries fungi that cause damping-off in seedlings. Use sterile potting mix for seed starting.
Fungi in non-sterile soil, combined with overwatering, poor air circulation, or lights too far from seedlings. It’s preventable with clean containers, sterile soil, and careful watering.
Moist but not soggy. When you squeeze a handful, it should hold together but not drip water. Water sparingly from the top or bottom-water to avoid oversaturation.
Miracle-Gro Moisture Control has given me consistent results for both seed starting and container growing. Look for mixes with compost, perlite, and peat moss.
For a detailed guide and journal for growing tomatoes, check out my Tomato Workbook on Amazon for $11.99.
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