Seaweed fertiliser is one of the most versatile natural feeds available, but like any tool, it’s most effective when used at the right time and in the right way. Understanding when and how to apply it—whether you’re feeding your houseplants in winter or giving your lawn a boost in spring—can make all the difference.
Why Timing Matters
Unlike synthetic fertilisers that dump nutrients into the soil, seaweed fertiliser works more holistically. It improves root strength, boosts microbial life in the soil, and encourages natural growth through hormones like cytokinins and auxins. That means it’s best used during periods of active growth or when plants are recovering from stress. Using it during dormancy or in excess isn’t harmful, but it may not provide the same benefits.
Spring: Wake-Up Call for Growth
Spring is one of the best times to apply seaweed fertiliser. Plants are coming out of dormancy, lawns are waking up, and seeds are being sown. Apply diluted seaweed feed to garden beds and vegetables once new growth appears. Lawns can benefit from a light foliar spray every 4 to 6 weeks starting in early spring. Houseplants, especially those on sunny windowsills, will also appreciate a monthly feed as they shift into active growth.
Summer: Support During Peak Activity
During summer, plants are working their hardest—flowering, fruiting, and growing quickly. This is when seaweed fertiliser really shines. Use it to support stressed plants during heatwaves, transplanting, or after pest treatment. Lawns can be fed every few weeks to maintain a deep green colour and improve drought resistance. Tomatoes, cucumbers, and herbs respond particularly well to regular seaweed feeding through the growing season.
Autumn: Strengthening Before Rest
As temperatures begin to cool, plants start to slow down. This is a good time to give one final round of seaweed feed to help roots develop and prepare for winter. It won’t force unwanted top growth, but it will support internal resilience. Lawns can be treated one last time in early autumn to help thicken roots. Indoor plants that continue growing in warm, light-filled rooms can still benefit from an occasional light feed.
Winter: Minimal Feeding, Maximum Care
In winter, most plants go dormant or slow their growth, especially in the UK. It’s generally not necessary to feed plants during this time, but seaweed can still play a role. A diluted spray can be used to help houseplants recover from dry indoor air or repotting. If you’re growing winter greens or using a greenhouse, seaweed can provide a gentle nutrient top-up without overwhelming the plant.
Application Tips
Always dilute your seaweed fertiliser according to the label—Aquaculture recommends around 10ml per litre of water for general use. For sensitive plants or seedlings, halve the strength. Apply with a watering can or misting spray, depending on the plant and season. Avoid feeding during intense midday heat or frost. As with any fertiliser, watch your plants and adjust based on how they respond.
Final Thoughts
Seaweed fertiliser can be used year-round if you understand your plants’ natural cycles. From early spring growth to summer resilience and autumn root strengthening, it’s a gentle but powerful tool for every stage. Whether you’re caring for houseplants, vegetables, or an entire garden, using seaweed seasonally ensures your plants get what they need—when they need it most.
