Gardening experts say that watering hydrangeas with seaweed before September arrives can boost blooms and keep the plants healthier. Seaweed is packed with nutrients that are not usually found in standard fertilisers, and it can improve soil health, encourage growth, and strengthen root systems.
Why Seaweed is Beneficial
Graham Smith MCIHort, a horticultural specialist from LBS Horticulture, told Ideal Home: "Seaweed is good for plants as it contains many useful plant nutrients, such as nitrogen, potassium, phosphate and magnesium. It is also rich in trace elements that are not usually found in common fertilisers, such as copper, zinc and manganese."
He added: "Flowering plants, particularly roses and hydrangeas, respond well to seaweed, producing more vibrant blooms and stronger stems."
Expert Endorsement
Gardening enthusiast and writer Mickey Gast also recommends incorporating seaweed into hydrangea soil. On the garden website Rural Sprout, she said: "One 'magic' ingredient that hydrangeas in particular seem to love is seaweed." She highlighted that seaweed "works really well" when applied during the plants' active growing period, spanning March to September.
How to Use Seaweed
Mickey prefers liquid seaweed "for ease of use", though it is also available in dry form as a concentrated powder. While you can apply clumps of brown seaweed to your plants, they should not be used as a substitute for fertiliser. Instead, experts recommend choosing a seaweed-based fertiliser that serves both purposes, as gathering seaweed from beaches is prohibited in the UK.
When using liquid seaweed, it is typically advised to use "one part seaweed liquid for 100 parts water". Therefore, for a two-and-a-half-gallon watering can, use approximately one hundred millilitres of liquid. Add this to the watering can and give it a gentle stir. Then apply it instead of regular watering at the hydrangea's base. The beneficial aspect is that it also functions as a "good foliar feed", meaning it "won't harm the plant" if the foliage gets watered as well.
