Kelp: A Gardener’s Best Friend

Why to Use Kelp in Your Garden

by Sandy Swegel

Our local garden club invited a rose expert from Jackson and Perkins to give us some winter inspiration this week. Rose growers are like tomato growers….they have their own little secrets and rituals to make their roses the best and the biggest. Our expert showed us pictures from his own garden that made me a believer in kelp. His plants treated with kelp and fertilizer were bigger and more robust than plants treated with just fertilizer If you are going to use soil amendments in your garden, kelp should be at the top of the list right after organic fertilizer.

So what does kelp offer?

Sea Minerals.
Kelp and other seaweeds are good sources of trace minerals that are often deficient in ordinary garden soil. So kelp is a good ingredient as a fertilizer…but not a substitute for your regular fertilizer.

Plant Growth Hormones.
OK, this is the real reason gardeners love kelp. Its natural plant growth hormones (cytokinins) stimulate extra growth in our plants and in our soil microbes. This is the “secret weapon” part of using kelp in your garden. Kelp stimulates roots, plant growth, flower production by virtue of the hormones even more than because of the vitamins and minerals.

Plant Health and Resilience.
Plants treated with kelp showed more drought resistance and bug resistance. Aphids, in particular, don’t like the taste of kelp and avoided kelp sprayed leaves. Anecdotally, I have found that a kelp foliage spray reduces powdery mildew.

How to Use Kelp

Kelp comes as kelp meal and as a liquid. An interesting thing about kelp is that when you apply kelp changes what kelp does for your plant. If you want sturdier roots, add kelp meal when planting to stimulate root growth. If you want more flowers on roses or tomatoes, apply it as a spray when your plants were budding. (Thanks researchers from the marijuana industry for these studies.) Some tomato growers use kelp weekly once tomatoes start to flower. If you are trying to improve your soil, apply meal or liquid to the soil once soil temperatures are above 60 or so when soil microbes are active. I like to use a weak kelp liquid spray weekly during hot spells in summer and spray all over the tops and undersides of leaves. It perks the plants up and gives the garden a lovely ocean smell. Plants absorb kelp better through leaves than through roots.

How Not to Use Kelp

More kelp isn’t better than small amounts of kelp. Don’t just throw it on your garden thinking more is better. Think about what effect you want. Do you want more tomatoes? Then applying kelp when the tomato is growing leaves but not making flowers yet will give you more leafy growth, not more tomatoes. On the other hand, a little kelp spray on your greens will increase the number and vitality of leaves.

Do Your Own Experiment
If you are going to add kelp to your repertoire, try a science experiment. Select a plant that you give kelp to and one a little further away that doesn’t get kelp. Do they behave differently?