How to Grow the Biggest Broccoli

Sow broccoli seed indoors about six weeks before the last frosts. Bury them about 1/2 inch deep in damp compost and place on a bright windowsill at a temperature above 50 degrees Fahrenheit. Gradually acclimatize your seedlings by exposing them to outdoor conditions.

Transplant your seedlings outdoors during the spring. Plant them in rich, well-drained soil that has been enriched with 50 percent compost or 3 lbs. of fertilizer per 100 square feet. For optimum growth, plant broccoli in slightly acidic soils with a pH between 5.8 and 6.5. Leave 18 to 24 inches between plants and 36 to 40 inches between rows.

Water your broccoli plants as soon as the surface of their soil starts to dry out, aiming to keep it evenly moist down to a depth of 6 inches. Ohio State University Extension advises that consistent moisture is necessary for good heads to form. Water in the morning so that the foliage is completely dry before nightfall. This prevents fungal diseases from forming. Provide a mulch of organic matter at least 3 inches deep to hold in moisture and stop weeds.

Fertilize your broccoli plants about a month after planting with 1 lb. ammonium nitrate per 100 feet of row. For optimum results, get your soil tested by a laboratory so that you know exactly which nutrients to provide.

Monitor your plants carefully and pick off any caterpillars or grubs. Treat persistent infestations of caterpillars or aphids with an insecticidal spray.