Comparison: Best Seaweed Fish Fertilizer (Updated | Dec 1st)

All three versions share the same 2‑3‑1 NPK ratio and core ingredients—fresh North Atlantic fish and seaweed—so performance is identical. The main distinction is volume: the 18 oz is ideal for small container gardens, the 36 oz suits medium‑sized beds, and the gallon provides the most cost‑effective option for large plots or frequent applications. Packaging size also influences how often you need to refill your mixing container, with larger bottles reducing the number of purchases.

A 2‑3‑1 blend supplies a balanced mix of nitrogen, phosphorus, and potassium that encourages both foliage and bloom development, making it versatile for mixed gardens. A 2‑4‑1 formula contains extra phosphorus, which promotes stronger root systems and fruit set, so it’s often preferred for heavy‑feeding vegetable crops. For pure ornamental flower beds, the 2‑3‑1 ratio typically yields more vibrant blossoms, while the 2‑4‑1 can boost vegetable yields without sacrificing flower quality.

Yes, both the 36 oz and 1‑gallon GS Plant Foods products are OMRI listed, meaning they meet the strict standards for organic production in the United States. They are derived from natural fish hydrolysate and North Atlantic kelp, with no synthetic additives, making them safe for certified organic farms and home gardens. The label also highlights their ability to improve soil microbiology, a key benefit for organic growers.

The GS Plant Foods 1‑gallon liquid fish & kelp fertilizer typically provides the lowest cost per ounce, especially when mixed at the recommended 2 oz per gallon of water for regular feeding. Neptune’s Harvest gallon‑size 2‑3‑1 fertilizer is also economical, but its price per ounce is usually higher than the GS brand. For gardeners needing frequent applications across many beds, the larger GS container delivers the best overall value.

Dilute the concentrate according to the label—most products recommend 1–2 tablespoons (or 2 oz) per gallon of water for a standard feeding. Apply the solution as a soil drench every 2–4 weeks, or use it as a foliar spray until the leaves are thoroughly wet for faster nutrient uptake. Consistent timing and proper dilution prevent nutrient burn and help maintain steady growth throughout the season.

Neptune’s Harvest uses a cold‑process method that retains fish proteins and oils while eliminating the typical fishy smell, so it is virtually odor‑free during mixing. GS Plant Foods also formulates its fish & kelp blend to be low‑odor, though a faint marine scent may be detectable when first opened. Both brands are liquid concentrates, so they mix cleanly with water and do not leave residue on containers when used as directed.

Absolutely. The liquid nature of all the listed products makes them safe for indoor use when diluted to the lower end of the recommended strength (typically 1 tablespoon per gallon of water). Apply as a gentle foliar mist or soil drench, being careful not to over‑water, and repeat every 3–4 weeks to keep houseplants thriving. Outdoor applications follow the same dilution guidelines but can be applied more heavily for larger soil volumes.