Making liquid kelp fertilizer at home requires just seaweed and water, using either a quick soak or a longer fermentation to extract the nutrients.
The process is straightforward: you extract the nutrients from seaweed into water, then dilute the resulting concentrate for use. Here’s exactly how to make liquid kelp fertilizer using two reliable methods, plus the dilution ratios you need to get right every time.
Method 1: The Quick Steep Method (3-Day Liquid Kelp)
If you need liquid kelp fertilizer in a few days rather than a few weeks, the steep method is the quickest choice. This gentle extraction produces a mild, balanced feed.
- Prep the seaweed. Rinse dried seaweed thoroughly to remove surface salt. Chop it into small pieces to maximize surface area.
- Soak. Submerge the chopped seaweed in water in a covered container. A non-airtight lid is best to let gases escape.
- Steep. Let it sit for 3 to 7 days. Stir it once daily. The water will gradually darken as it extracts the nutrients.
- Strain. Pour the liquid through a fine mesh strainer or cheesecloth. The liquid is ready to use immediately.
The result is a dark, nutrient-rich liquid. For a commercial-grade alternative without the wait, check out our roundup of the best kelp liquid fertilizers on the market.
Method 2: The Fermentation Method (Stronger Concentrate)
The fermentation method breaks the seaweed down completely, yielding a more potent concentrate that stores well. This is the traditional approach used by serious gardeners.
- Prep and submerge. Rinse and chop the seaweed, then place it in a bucket. Cover with water, leaving some headspace. Use a non-airtight lid or a cloth cover to allow airflow and reduce pressure.
- Brew. Stir the mixture every few days. In warm weather (above 65°F), it takes about 2–3 weeks. In cooler weather, it may take 2–3 months.
- Strain. Once the solids have broken down into a thick, dark liquid, strain out the remaining fibers through cheesecloth.
This method produces a stronger fertilizer, but it also creates a stronger odor during the brewing process—keep the bucket in a shady spot away from your living spaces.
How to Use Your DIY Liquid Kelp (Dilution Ratios)
Concentrated DIY liquid kelp is potent and must always be diluted before hitting your plants. The right ratio depends on how you apply it.
| Application Method | Dilution Ratio (Fertilizer:Water) | Notes |
|---|---|---|
| General Soil Drench | 1:20 | Use every 2 weeks during the growing season. |
| Foliar Spray | 1:10 | Apply in the morning or evening when stomata are open. |
| Hose-End Sprayer | 1:16 | Convenient for treating large lawn areas quickly. |
Store the strained concentrate in a cool, dark place. For foliar application, strain it extra fine to prevent clogging your sprayer nozzle.
Common Mistakes to Avoid
The most common mistake is using an airtight lid, which creates a pressure bomb and a terrible smell when opened. Always use a loose lid or cloth cover. Don’t skip rinsing the salt from the seaweed, and never apply the concentrate without diluting it first—it is very potent and can burn plant roots in its raw form.
FAQs
How long does homemade liquid kelp fertilizer last?
Stored in a cool, dark place, the concentrate can last for several months to a year. If it develops mold or a rotting smell, it is best to discard it and start fresh.
Can I use fresh seaweed from the beach?
Yes, but it is crucial to rinse it very thoroughly to remove surface salt. Too much salt in your fertilizer can damage lawn and garden soil over time.
Why does my batch smell so bad?
A strong smell usually means the mixture went anaerobic or the container was sealed too tightly. Using a loose lid and stirring occasionally introduces enough oxygen to keep the smell manageable.
References & Sources
- Biostim. “How to Make Liquid Seaweed Fertiliser.” Professional how-to guide on seaweed fermentation and steeping methods.