Seaweed Benefits for Your Garden

The word “seaweed” has one of the shortest definitions in the Canadian Oxford Dictionary. It is simply laid out as “any of various algae growing in the sea or on the rocks on the shore.” With an introduction like that, it may take a stretch of the imagination to picture a pile of seaweed performing miracles in our garden.

So what is so magical about seaweed? It is a rich, non-polluting source of natural organic minerals and trace elements, amino acids, carbohydrates and several essential plant growth hormones. It hastens seed germination, stimulates root growth, and increases the production of blossom and fruit set. It increases the capacity of the soil to retain water, giving extra protection in times of drought. Seaweed also acts as a soil “conditioner,” stimulating microbial activity, and is an excellent source of organic matter. In addition, seaweed reduces insect and disease problems, and can even increase a plant’s resistance to cold and frost damage. Pretty impressive.

The big questions for most of us are what kind to use, where to get it and when to use it.

How to Use Seaweed in Your Garden

Bill Rose farms organically in Short Beach, NS. He has used seaweed for as long as he could drive a horse to the shore to harvest it. Bill’s favourites are rockweed (Ascophyllum nodosum)—the kind that has the plump balls on the fronds that we used to pinch between our fingers when we were kids —and Irish moss (Chondrus crispus), the curly purple-looking stuff we sometimes see drying roadside in our coastal villages.

“It comes up with the tide in wind rows. One day it will be there and the next day you get an east wind and it’s gone, so you have to go with the tide,” he said, adding that there’s always a bigger bounty after a storm. Bill’s soil is rich and brown. It is loaded with various kinds of worms which is an added bonus for gardeners. “You get all the micronutrients from the sea. It’s fairly high in nitrogen and potash and it sweetens the ground. It makes the soil much easier to work with. It just crumbles up and stays nice and soft.”

This year Bill experimented with a new way of growing potatoes. It was a huge success. “First I put straw (on the ground) in the fall to rot up the sod. In the spring, I took a fork and pushed the sod aside, then I put a good layer (about eight inches) of year-old rockweed on top and ran the tiller to mix it up a bit. Then I made a little trench with my hoe, dropped the potato seed, and pulled a little dirt over. As soon as they came up, I put a good layer of straw all around.” The beauty of planting potatoes this way? No weeds, no hilling, no potato bugs, and the ground is so soft that you can dig the potatoes with your hands!

Let it Rot

The trick with seaweed is to let it sit all winter. If you mix some straw in your pile, it will have a chance to aerate and it will decompose faster. I’ve heard of someone who got into big trouble when he tried to till seaweed into his garden—fresh from the beach. I suspect he also had a lot of kelp mixed in, which can be thick and rubbery. He ended up untangling miles of mangled, gooey strips of seaweed from his tines.

Another approach is to spread a layer of fresh seaweed on your garden in the fall, after everything is harvested. It will crumble over the winter and you’ll be ready to proceed in your normal way next spring.

Alternatives to Fresh Seaweed: Liquid or Dried

For those who cannot gather their own seaweed at the shore, check the garden centres for dried, ground seaweed products. It is sometimes sold as a “meal” and usually looks like large flakes of ground pepper, only olive green or brown in colour. For home gardening, use three pounds per 100 square feet or two pounds per 100 foot row; 10 pounds per 1,000 square feet of lawn; and two to three per cent total volume of potting mixes.

Another product to look for is a seaweed extract that can be purchased in dry, granular form. It looks like plump black or brown poppy seeds, and dissolves in water to produce a dark liquid. If you can find this product, mix it in a ratio of one part granules to 50 parts water. You may be able to buy it premixed in liquid form.

Liquid seaweed can be used in many ways. Try it as a drench for transplants. You’ve likely seen your precious plants keel over from the trauma of going from the greenhouse or garden centre to the ground. Using seaweed at transplant time eliminates the shock. Simply soak each tray just before you plant. When I farmed, I used this method with thousands of transplants every year. I never had a plant droop or die. You can also make “seaweed tea.” Put several cups of decomposed seaweed in a bucket, cover with warm water and let it set for several days. If you strain off the liquid, the results should be similar.

Liquid seaweed is also great as a foliar spray. As soon as the first true leaves sprout—or as soon as the leaves come out for established fruit trees, flowers and vegetables —spray them. Repeat the process two to three weeks throughout the growing season. You can do this at any stage, as seaweed is non-toxic and harmless. This procedure also helps your plants withstand some of the effects of cold nights and frost damage.

Author Sandra Benitez once said: “In the biting honesty of salt, the sea makes her secrets known to those who care to listen.” Isn’t it time you headed for the shore?