Seaweed is largely under-appreciated in the gardening world, classed merely as a soil conditioner or a fertiliser. Its benefits are so extensive, though, that it really should be given top billing in any maintenance programme for lawns, fine turf or garden plants.

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Seaweed contains over sixty minerals and trace elements, along with numerous biostimulants, and it also contains iodine, which is an excellent disease suppressant. I first learned what it could do during my years as head greenkeeper at Lahinch, on the west coast of Ireland, where the sea supplied it by the tonne — and I have used it on fine turf ever since, right through to the bowling and golf greens I have built and managed in Scotland. As you can probably tell, I’m a bit of a fan of our sea-borne, slippery friend, and no wonder. All of the above reasons make seaweed a top-class supplement for both grass and garden.

The Wonder of Seaweed in Your Garden

Seaweed can be used as a fertiliser or soil conditioner in many different forms, for example:

• Seaweed can be dug into your soil in its raw form, straight from the beach
• Seaweed can be dried and either granulated or powdered (sold as seaweed meal)
• the goodness can be extracted from seaweed to form a concentrated seaweed liquid.

In modern fertiliser use, liquid seaweed makes a highly efficient base for the nutrition of a wide variety of plants. This is because it can be safely mixed with most of the commonly used sources of nitrogen, phosphate and potassium, along with supplements like iron. The seaweed stimulates the soil bacteria which, in turn, help to release much of the nutrient content. In many cases these nutrients are locked up in the soil and not available to plants, whether you’re feeding grass, tomatoes, vegetables or flowers. Seaweed combats this, helping you to make the most of any nutrients being applied and reducing the quantity required for healthy growth.

To add to the list of benefits, seaweed is also valuable in helping to break down organic matter. This is a particular benefit when treating turf, where thatch can be a serious problem if not managed properly — it’s one of the reasons I consider it an essential part of fine turf maintenance. Finally, as if we haven’t heard enough about the wonders of seaweed, it’s also a very high quality food supplement for both animals and humans. But let’s not get greedy — before we go and eat up our entire supply, let’s first deal with its uses and benefits on our lawn and garden.

Seaweed Fertiliser: Discovering the Benefits

The benefits of using seaweed on plants were first discovered many years ago by farmers living and working beside the sea. They would harvest the seaweed from the shore as it was washed in by storms, then spread it on the land prior to planting the crops. The benefits were particularly noticeable on potatoes, always susceptible to disease, as the fields treated with the seaweed consistently produced better crops with very clean skins.

One side effect of seaweed use was the presence of a very distinctive flavour in the potatoes, something quite noticeable when compared to normal potatoes. This is no longer an issue, though, now that growers have access to very easy-to-apply granular fertilisers. This variation of the seaweed fertiliser doesn’t have the same side effect, the strange taste disappearing during drying or granulation.

The seaweed fertiliser was also found to improve soil quality over a number of years. This is now known to be because the alginates act as a flocculant, breaking down heavy soils into a crumbly, free-draining material. Conversely, almost fifty percent of seaweed’s constituents are humus-forming, so light sandy soils become more fertile and less prone to drought damage.

How Can Seaweed Help Your Garden?

As you will see from the pictures above, seaweed can work wonders for your garden in many different ways. The following are examples of how seaweed can help you in your garden:

• Flowers tend to produce more vibrant colours with an application of seaweed
• Vegetables produce healthier, disease-free crops
• Seaweed-treated grass will be greener and produce a healthy, dense sward, providing other maintenance work is carried out correctly
• Seaweed helps to prevent club root and blossom end rot
• Seaweed will prevent blight and scab on potatoes
• Dusting plants with seaweed powder deters blackfly and greenfly
• Carrots dusted with seaweed powder seldom suffer damage from carrot fly

On fine turf, seaweed also earns its keep in dealing with specific problems: I have used seaweed meal as part of the programme for curing dry patch and compaction on a bowling green, where its water-holding, humus-forming character makes a real difference on droughty, thatchy surfaces.

Applying Seaweed Fertiliser to your Garden

If you are lucky enough to have access to fresh seaweed, it can be spread straight onto the garden. Although it can be dug into the drills fresh with potatoes, the best way is to collect it during autumn and winter, when stormy seas will provide you with ample material. Then you can spread it onto the surface of the vegetable garden, where it will break down a little over the cold season, suppressing weeds as an added bonus. When spring comes around, you can dig the material straight into the soil.

Seaweed can also be used as a mulch in and around shrub beds and annual and perennial borders, where it will break down slowly, releasing nutrients into the soil while again acting as a natural weed suppressant. The one exception is to avoid treating rhododendrons, azaleas and other acid-loving ericaceous plants. This is because seaweed creates quite alkaline conditions, not conducive to these types of plants.

Looking for Pre-Prepared Seaweed Fertiliser?

If you don’t have easy access to the beach, there is a good range of pre-prepared seaweed fertiliser on the market. You’ll find seaweed extract as one option, and this organic concentrated seaweed fertiliser is another good choice. For UK readers, we also stock the products I use myself in the Lawns For You shop: seaweed meal for soil improvement and dry patch work, and a turf care liquid fertiliser for feeding through the growing season.

Not sure which form suits your garden best? I’ve written a separate guide to help you choose: What Seaweed Fertiliser is Right For Your Garden.

If you would like advice for your own lawn rather than general guidance, I offer a personalised online lawn care plan, wherever you are, and lawn care services in person around Dumfries.

If you have any experience of using seaweed yourself, I’d love to hear about it. Please leave me a comment below letting me know what you think about seaweed for lawn and garden care.