Pond Scum & Algae as Compost: Turn a Nuisance into Nutrient-Rich Fertilizer

Pond scum and algae are living, nitrogen-rich organisms that break down quickly in compost, adding potassium and phosphorus too. Spring pond cleaning is the perfect time to harvest this free fertilizer.

How to Compost Pond Scum

1. Remove with pool skimmer or rake; drain excess water.
2. If water is salty, rinse with hose.
3. Build pile: 4–6 inch brown layer (straw, cardboard, leaves).
4. Mix scum with other greens (veggie scraps, coffee grounds, fresh grass); spread 3 inches over browns.
5. Top with handfuls of garden soil (adds microbes).
6. Moisten lightly; repeat layers until pile ≥3 ft deep.
7. Pile should heat within 24 hours. Turn weekly or when cooling. Check moisture every 2–3 days (damp sponge feel).

Using the Finished Compost

• Dark brown, crumbly, earthy = ready.
• Spread 3 inches before spring planting; dig in or use as mulch.
• For potting mix: blend 1:1 with perlite or coarse sand.

A win-win: cleaner pond, richer soil.