Short answer: 1 level teaspoon (about 5 grams) of COMPLETE 12-4-8 per gallon of water delivers roughly 158 ppm nitrogen, a solid standard feeding rate for most actively growing plants. Use half that for gentle maintenance feeding and up to double it for heavy feeders.
This guide gives you the exact rates, the PPM behind them, and the simple math so you can mix any strength you need.
The quick rate chart
| Feeding goal | Per gallon | Approx. PPM Nitrogen |
|---|---|---|
| New / repotted / seedlings | ¼ tsp (1.25 g) | ~40 ppm |
| Light / maintenance (every watering) | ½ tsp (2.5 g) | ~79 ppm |
| Standard / production (every 7–14 days) | 1 tsp (5 g) | ~158 ppm |
| Heavy feeders (citrus, tomatoes, figs, bananas) | 1½–2 tsp (7.5–10 g) | ~238–317 ppm |
| Foliar spray | ¼ tsp (1.25 g) | ~40 ppm |
Mix thoroughly until fully dissolved before applying. Because it's a fresh-mixed water-soluble powder, make only what you'll use.
What you're actually delivering at the standard rate
At the standard 1 tsp (5 g) per gallon, here's the full nutrient picture, not just nitrogen:
| Nutrient | PPM at 1 tsp/gal |
|---|---|
| Nitrogen (N) | ~158 ppm |
| Phosphate (P₂O₅) | ~53 ppm |
| Potash (K₂O) | ~106 ppm |
That 3-1-2 balance in the jar carries straight through to the 3-1-2 balance in the solution, roughly three parts nitrogen to one part phosphorus to two parts potassium, the proportion most actively growing plants use.
The math, so you can mix any strength
PPM (parts per million) is just milligrams of a nutrient per liter of water. For nitrogen from this product:
PPM nitrogen ≈ grams of product × 2.64 (per gallon)
That comes from the 12% nitrogen content divided across a gallon (3.785 liters). So 5 grams × 2.64 ≈ 158 ppm, 2.5 grams × 2.64 ≈ 79 ppm, and so on. Want a target PPM? Divide it by 2.64 to get grams per gallon. Targeting 200 ppm N? That's about 7.6 grams, or roughly 1½ teaspoons.
A level teaspoon of this powder weighs approximately 5 grams. Always level the scoop for consistency, a heaped teaspoon can carry 50% more than a level one.
How often to feed
- Every watering (constant feed): use the light rate, ½ tsp per gallon. This suits steady growers and is gentle enough for regular feeding.
- Every 7–14 days: use the standard rate, 1 tsp per gallon, watering with plain water in between.
- Heavy feeders in peak season: the higher rate every 1–2 weeks, watching the plant's response.
- Dormancy / slow growth: reduce feeding during periods of slow growth, short days, or cold.
Tips for clean results
- Dissolve fully before applying. Stir until the water runs clear, especially in cold water, which dissolves powder more slowly.
- Water thoroughly after feeding so nutrients distribute through the root zone rather than concentrating at the surface.
- For foliar spraying, use the low rate, spray in early morning or evening, and avoid hot, sunny conditions to prevent leaf marking. Filter the solution if your sprayer has a fine nozzle.
- Start conservative on new or stressed plants and work up as they establish.
Frequently Asked Questions
How much 12-4-8 do I use per gallon? For most plants, 1 level teaspoon (about 5 grams) per gallon every 7–14 days. Use ½ teaspoon for gentle feeding every watering, or up to 2 teaspoons for heavy feeders.
What PPM is 1 teaspoon of 12-4-8 per gallon? Approximately 158 ppm nitrogen, along with about 53 ppm phosphate and 106 ppm potash.
Can I feed 12-4-8 every time I water? Yes, at the light rate (½ tsp per gallon, ~79 ppm N). Water thoroughly and follow the rate chart.
How do I hit a specific PPM target? Divide your target nitrogen PPM by 2.64 to get grams of product per gallon. For example, 150 ppm ÷ 2.64 ≈ 5.7 grams.