The widely used Masterblend recipe combines three dry ingredients in a 2:2:1 ratio by weight. For strawberries, mix it weaker than the standard recipe. Always check the instructions on the bags you buy, since they are the final word.
The Three Parts
- Masterblend 4-18-38: the base formula, supplying phosphorus, potassium and trace elements.
- Calcium nitrate: supplies calcium and most of the nitrogen.
- Epsom salt (magnesium sulfate): supplies magnesium and sulfur.
The Standard Ratio
The recipe most growers quote is 12 grams of Masterblend, 12 grams of calcium nitrate and 6 grams of Epsom salt for 5 gallons of water. That works out to roughly 2.4, 2.4 and 1.2 grams per gallon, often rounded to 2, 2 and 1.
Mixing for Strawberries
Strawberries are sensitive to salt and prefer a milder solution than tomatoes. Start young plants at about half the standard recipe, and run established plants at half to three-quarters. If you have an EC meter, aim for roughly 1.0 to 1.5 mS/cm.
Why Each Part Is Dissolved Separately
Calcium nitrate reacts with the phosphates and sulfates in the other two ingredients when they meet in concentrated form, and the result is a solid that plants cannot use. To avoid it:
- Weigh each ingredient with a digital scale. Spoon measures are not accurate for powders.
- Dissolve the Masterblend completely in the full volume of water.
- Dissolve the Epsom salt in, and stir.
- Dissolve the calcium nitrate last, stirring until the water is clear.
Never mix the dry powders together, and never combine them in a small amount of water.
After Mixing
Test the pH and adjust it to between 5.5 and 6.5. Store the dry ingredients sealed and dry, where they keep for years.
Related guide: Nutrients for Kratky strawberries.
