Kelp is key for giving your organic garden a microbial boost

Every fertilizer package has a so-called “NPK” listing representing the percentage of nitrogen, phosphorus and potassium (which are the primary essential elements needed by plants) on the front of the package. Sooner or later, you learn about the rest of the essential elements, calcium, magnesium and sulfur. And, a yellowing leaf or a cat-fat tomato might send you running to find a cause and you discover the micronutrients boron, chlorine, copper and iron.

There are 17 elements a plant needs to grow and reproduce. These are in the soil. Nothing else is needed, save hydrogen, carbon and oxygen which plants basically get from the air.

Think about it. You can’t play a game of cards with only 17, but everything we see, eat and smell in a plant is made out of those mere 17 elements. This is because there are an astounding 355,687,428,096,000 possible combinations of those elements — literally trillions available for biosynthesis of what the plant requires.

Take away one of these 17 elements and your plant won’t make it to produce seeds. Sure, even if you only have the top 7 or 8, the plant will grow but perform weakly; it will have problems as it won’t fully mature. As an aside, most soils also have the micronutrients your plants will need, so unless clearly labeled, most fertilizers do not contain them.

[‘Teaming With Microbes’ podcast: A recipe book for feeding the microbes in your soil]

In an organic system, organic matter provides all of these nutrients. This matter is broken down by microbes, which put the resultant nutrients into plant-useable form (see “Teaming With Microbes”). You don’t want to do anything to disturb their work such as sterilizing, tilling or using chemical fertilizers.

OK, organic fertilizers have what you need. However, the big gripe about organic gardening is that you can’t add fast acting fertilizers. Microbes take a while to do their thing, so if your plant has a nutrient deficiency, it may take too long for the microbes to correct it under an organic system.


To counteract this problem, organic gardeners (and I assume all readers of this column are growing organically) consider using kelp. Most use it because it provides plants with some the needed nutrients, especially the micro and trace elements. More important, however, are the phytohormones contained in kelp.

Phytohormones do lots of things like help strengthen plants, make them grow faster, cause cells to stretch, and regulate the timing of fruit formation and drop. Kelp’s main phytohormones are auxin, gibberellin and cytokinin. The latter greatly increases cell division, causing growth of roots and tips and also positively impacting photosynthesis (which also obviously beneficially impacts growth).

I guess you could simply say kelp helps plants grow efficiently. It also helps microbes by feeding them. In doing so, it increases the decay of organic matter into plant-useable nutrients.

I can remember collecting seaweed (probably not kelp, but related) as a kid, and tossing it into the compost pile. You can actually find kelp on our West Coast beaches and do the same thing or put it on your gardens in the fall.

Commercial kelp is much more accessible, however, and can be purchased in powdered or granular forms. It won’t burn roots or harm seeds, so you can mix it in your seed-starting mix or sprinkle some on roots when you transplant up or outdoors. You can’t apply too much, which is why some folks cover their garden beds using 50-pound bags of the stuff. I think that is a bit excessive.

To start using kelp, buy a box or jar of powdered kelp. Mix a handful into seed starting soil and put some into each planting hole when you transplant this spring. It will help your plants make the transition to being in the ground, provide some trace elements and help them better utilize the nutrients already in your soils.

Jeff’s Alaska Garden Calendar

Alaska Botanical Garden: Join. Join. Join. What are you waiting for. Discounts and first call at The Nursery, events and more, more, more. Plus you are supporting a terrific economic driver.

Recycle pots: Earth Day is April 22. There is a customer appreciation and recycling event at Habitat ReStore at 1200 W. Northern Lights Blvd. Alaska Plastic Recovery: Bring your #1, #2, #4, and #5 plastics for local recycling into plastic lumber! Learn about Patrick Simpson’s mission, and check out samples of his product.

Flowers to start from seed: Dahlia, schizanthus, nigella, phlox, portulaca, nemesia, marigold and nasturtiums.

Vegetables: Broccoli and cauliflower. Stagger if possible so you can stretch out harvest season.

Gladioli: Lots of concern about the height some have reached. Not to worry as you bury them a few inches deeper when planted outdoors.

(Listen to the new podcast, “Teaming WIth Microbes” wherever you hear podcasts and read the Teaming Quadrilogy)

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.