Cover crops can add valuable organic material to your garden soil

Cover crops are extremely important soil food web tools.

Anyone listening to the “Teaming With Microbes” podcasts knows I am into them. Depending on which you use, these plants are capable of breaking up tight soils, improving drainage and soil structure and can be used to attract beneficial insects to the garden. The most famous of all are those cover crops that fix nitrogen from the air making it useable by plants.

I don’t write about cover crops enough. Perhaps this is because they are normally grown during the offseason and, unfortunately, nothing grows in Alaska during our offseason (unless it is grown inside). It is hard to break up frozen soil with roots and there will not be any nitrogen fixing because the special bacteria infect living roots, not frozen ones.

In other places where you can plant winter crops, the results can be amazing. One of my friends landed the job of refurbishing the landscaping around the famous Gateway Arch in St. Louis. The soil was so compacted by all the tourists that it needed help. So, he planted the entire grounds with hundreds of a special kind of giant turnip, of all things, which grew all winter, much to the puzzlement of those who visited the site. In the spring the soil was ready. This is how you get away with not rototilling.

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Listen to the podcast with Jeff and Jonathan White:

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We can use cover crops here. All of the offseason nitrogen-fixing cover crops will grow during our season. These include red clover, crimson clover, vetch, peas and beans. They attract rhizobia bacteria to then form root nodules in which they fix nitrogen. You can even inoculate them with these bacteria purchased from nurseries.

Note that any fixed nitrogen is mostly used by the host plant and rightly so, as it spends a lot of energy to support these bacteria. Once the cover crop is allowed to die and decay, the useable nitrogen is released for the next crop. Some fixed nitrogen usually leaks out into the soil, however, and is usable by, say, the tomatoes, peppers or cucumbers in whose pot the clover is planted.


If you want to break up garden soils, you can plant giant turnips during the season. Carrots will work, as will regular turnips and those long, cylindrical radishes. You could use a fallow part of your garden if you have one. Or you could plant them in rows with more wanted crops planted in between.

Both kinds of cover crops will add much appreciated, organic matter to your soils if you leave them to decay when the season ends. In addition, many of our regular crops can act as effective cover crops. The trick is to leave as much of the plant out in the garden post harvest so it can decay in the fall, winter and spring months. In essence, harvest and eat the snap peas, but leave the roots and pea leaves.

This year I am trying fava beans, a well-known cover crop. I picked up a few packets of seeds at a seminar on cover crops, but have never grown them. Wow. I can see where they will result in lots of organic matter. Already they are huge plants. Come fall, there will be plenty of beans to feed the family, but lots and lots of plant to leave to feed the soils.

Jeff’s Alaska Garden Calendar:

Alaska Botanical Garden: What is in bloom there (and hopefully next year in your garden because you visit the ABG Nursery). Check out

Harvest: Get going on those beans and snap peas. If you don’t pick them, the plants will slow down and stop producing. Kohlrabi loses texture and taste when it gets bigger than a hardball. Don’t forget all those radish you planted.

Stake plants: Take advantage of a sunny day to stake plants so they don’t fall to the ground on a rainy one.

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.