Get the soil food web working so your plants will thrive

The loyal reader knows I am an organic gardener. My first book was on the soil food web and popularized the concept that plants produce carbon-based exudates designed to attract specific microbes. These feed, protect the plant and improve soil structure. Organic gardeners use the soil food web.

Obviously, the key to the soil food web, besides the plant-producing exudates, is to ensure there are ample numbers and kinds of microbes for the plant to attract and to choose from. This begs the question as to what kind of soil to use and how to handle seeds. What are the best things you can do at the start of the season to employ the soil food web efficiently?

Let’s start with soil mixes. You will find soilless seed starting mixes, soil-based seed starting mixes and compost-based mixes. In case you are wondering how you can use a soilless seed starting mix in a soil food web system, you need to know that most of the initial microbes a plant utilizes for nutrition are in and on the seed itself. This is why it is not a good idea to sterilize seeds.

The idea behind seed starting mixes is that they are very light and loose so that seeds can easily germinate and roots don’t have a difficult time channeling into and through the soil. As an astute gardener, you need to pay attention to what is use in these mixes, however.

Peat, I must point out, is a universal no-no when it comes to gardening these days so don’t use it in starting or other soil mixes. More and more soilless seed starting mixes are now coconut coir based, made from coconuts obviously, and environmentally acceptable. You will also find perlite and vermiculite, both natural products which are fine. Some mixes contain diatomaceous earth which serve to replace peat.

OK, many soilless mixes are heated to kill pathogens that might cause problems like damp-off, which will kill seedlings. These “sterilized” mixes work because the seed carries the necessary microbes that will populate the soil at germination.

Potting mixes contain heavier soils. The big advantage to using them is that they contain more nutrients and microbes that supplement those seed-borne microbes. Thus they last longer as plants grown in soilless mixes usually need to be put into real soil shortly after they develop leaves or feed.


Then there is compost. There are lots and lots of soil food web microbes in compost. Pathogens are usually kept in check by the diversity of microbes, but those that can cause problems may enter a plant before the diversity can take them out. This is why seedlings can suddenly die back. This is, damping-off — wherein seedlings simply keel over dead — and why many gardeners transplant into compost, but only after plants get several leaves. Good air circulation, by the way, is a great why to help ward off damping.

So much for the mixes. What about the seeds? There is always a concern that seeds be organic. The fact of the matter is that commercially available seeds are organic unless there is a specific indication that the seed is coated, which is usually a process reserved for agricultural plantings. The only thing you want to coat your seeds with is an endo mycorrhizal fungi mix, so roll yours in some or sprinkle it over seeds.. Do mix some of this into the starting soil so that roots will become infected as the roots come into contact

I do not advise fertilizing soils before starting seeds in them. Get the seeds up and running first. Once germination occurs, consider adding kelp as it has been shown to be extremely effective in helping microbes work together to run the soil food web. A good start to the season is to get that soil food web working.

Jeff’s Alaska Garden Calendar:

Alaska Botanical Garden Spring Conference: The conference is March 23-24 on the second floor of the Dena’ina Civic and Convention Center. This is an important conference for Alaska gardeners, a veritable must-attend event. Registration is required.

Flower seeds to start: Lobelia (seeds need light), snapdragons (seeds need light, cool), carnation, verbena, pelargonium, fibrous begonia, dahlia from seed and sweet peas.

Herbs to start: Lavender, lovage, lemon balm, sage

Vegetables to start from seed: Celery, leeks

Jeff Lowenfels

Jeff Lowenfels has written a weekly gardening column for the ADN for more than 45 years. His columns won the 2022 gold medal at the Garden Communicators International conference. He is the author of a series of books on organic gardening available at Amazon and elsewhere. He co-hosts the "Teaming With Microbes" podcast.