Only apply high nitrogen to strawberries early in the spring or when first planting them. 10-10-10 commercial fertilizer can be sprinkled at the base of the plants during the fruiting season. Then some higher nitrogen fertilizer after fruit bearing season before overwintering, say after September. Nitrogen will help the vines and runners get a good start, but during the growing season nitrogen will grow the green parts and restrict berry growth. Fertilization following this formula can be from either commercial or organic sources. Mulch and organics is what strawberries like and don't overwater.
