GS Plant Foods vs. Neptune's Harvest: Fish Fertilizer Compared

If you've searched "neptune's harvest fish fertilizer" or "neptune's harvest vs" anything, you already know it's one of the most established organic fish fertilizers on the market — in garden centers and farm stores since the 1970s. We think our Organic Liquid Fish Fertilizer and Fish & Kelp Liquid Blend are worth a look too — so here's an honest, side-by-side breakdown instead of a sales pitch. Where Neptune's Harvest wins, we say so.

The short version

• Both are cold-processed fish hydrolysate — not heat-treated fish emulsion. This is the biggest myth in fish fertilizer shopping: not every "fish fertilizer" is hydrolysate, but both of these are. Neither brand has an "overcooked" odor or nutrient loss problem to solve here.
• GS Plant Foods costs less per bottle at Quart and Gallon sizes — the sizes most home gardeners actually buy.
• Neptune's Harvest's 5-Gallon pail undercuts GS's on price at that bulk size.
• Neptune's Harvest has the broader retail footprint (Tractor Supply, Walmart, Lowe's, independent nurseries) if you want to buy in person.
• GS Plant Foods ships direct and small-batch, with a matching Fish & Kelp blend priced close to its fish-only formula.

Processing: hydrolysate vs. hydrolysate

This one's a wash, and we're not going to pretend otherwise. GS Plant Foods' Organic Liquid Fish Fertilizer is a cold-processed fish hydrolysate — no heat, so amino acids, enzymes, and natural oils stay intact. Neptune's Harvest describes its Hydrolyzed Fish Fertilizer the same way: a "unique cold process" that "protects heat-sensitive nutrients." Neither is the heat-treated fish emulsion (like Alaska-style fertilizers) that gives fish fertilizer its reputation for a stronger, lingering odor.

If you see "fish emulsion" used loosely to describe either of these products elsewhere online, that's imprecise — both brands are hydrolysate by their own product descriptions.

Full comparison

Fish & kelp blends (matching NPK 2-3-1)

How pricing tends to shake out

We're deliberately leaving exact numbers out of the tables above — both brands adjust pricing throughout the year, and a hardcoded price table goes stale fast. Here's the pattern that's held true across our research instead:

• At the sizes most home gardeners buy — a Quart or a Gallon — GS Plant Foods consistently prices noticeably below Neptune's Harvest's equivalent size, for both the fish-only formula and the fish + kelp blend.
• GS Plant Foods prices its Fish & Kelp blend within a dollar of its fish-only formula. Neptune's Harvest charges a meaningful premium for its Fish/Seaweed Blend over its Hydrolyzed Fish Fertilizer at the same size — so the "why pay more for the blend" math favors GS if you want both fish and kelp in one bottle.
• That gap narrows — and can flip — at bulk sizes. At the 5-Gallon pail tier, Neptune's Harvest has come in cheaper than GS Plant Foods' equivalent, on both the fish-only and blended formulas. If you're fertilizing a farm, large property, or buying a season's supply at once, it's worth comparing current 5-Gallon pricing directly rather than assuming the small-size pattern holds.
• Check current listings before you buy. Since pack sizes, dilution rates, and pricing all shift independently on each site, the fairest comparison is the live price divided by however many diluted gallons your specific use case calls for — not the sticker price alone.

Choose GS Plant Foods if...

• You want the lower entry price to try a fish fertilizer at Quart or Gallon size.
• You want a fish + kelp blend priced close to fish-only, rather than paying a real premium for the blend.
• You want to know exactly which seaweed you're feeding your plants — we name the species and origin (Norwegian Ascophyllum nodosum).
• You'd rather buy fresh, direct-shipped, small-batch product and skip the retail shelf.

Choose Neptune's Harvest if...

• You're fertilizing at scale — its 5-Gallon pail has priced lower than GS's equivalent in our research, though it's worth confirming current pricing for your order size.
• You want to buy in person at Tractor Supply, Walmart, Lowe's, or a local nursery today.
• You value a 60-year track record over a newer direct-to-consumer brand.

Frequently asked questions

Is GS Plant Foods fish fertilizer the same as Neptune's Harvest?

Not identical, but similar in method: both are cold-processed fish hydrolysate, not heat-treated fish emulsion. GS Plant Foods' Organic Liquid Fish Fertilizer is NPK 2-3-1; Neptune's Harvest's Hydrolyzed Fish Fertilizer is NPK 2-4-1. Both are OMRI Listed.

Is fish hydrolysate better than fish emulsion?

Generally yes — the cold process used by hydrolysate fertilizers (including both GS Plant Foods and Neptune's Harvest) preserves amino acids, enzymes, and natural oils that heat destroys in true fish emulsion. If you're comparing either of these brands to a heat-treated fish emulsion product, that's where the hydrolysate advantage applies — not between GS and Neptune's, which use the same processing method.

Does GS Plant Foods fish fertilizer smell?

It has a light ocean scent that fades after application, per our own product listing. One verified customer review notes it "smells strong" during mixing and recommends preparing it outdoors — which is true of most fish-based fertilizers, hydrolysate or not.

Which is cheaper, GS Plant Foods or Neptune's Harvest?

It depends on the size. GS Plant Foods is cheaper at Quart and Gallon sizes — the sizes most home gardeners buy. Neptune's Harvest is cheaper at the 5-Gallon pail size.

Explore more

• Organic Liquid Fish Fertilizer – NPK 2-3-1
• Fish & Kelp Fertilizer Organic Liquid Blend
• Organic Liquid Kelp Seaweed
• Shop all Specialties (fish, kelp & more)
• What Is Fish Fertilizer? Benefits & How to Use It
• Mixing Matrix: dilution rates for every GS Plant Foods product