Zone 5
In Zone 5’s short season, early-maturing heirlooms need indoor starts by mid-February and frost-safe outdoor planting after mid-May.
Start seeds 6–8 weeks before the average last frost date. Use bottom heat to maintain optimal soil temperatures for germination—most heirloom tomatoes require minimum soil warmth to sprout reliably. Seedling trays under grow lights on a south-facing windowsill work, but supplemental lighting prevents legginess and strengthens stems. By mid-March, switch to cooler nights (55–65°F) to harden off seedlings gradually.
Transplant only when night temperatures consistently stay above 50°F and soil reaches at least 60°F at 4 inches deep—often near or just after the average last frost date. Prepare beds with compost and a balanced organic fertilizer. Use black plastic mulch to warm soil faster and row covers to retain heat at night. Indeterminate types like Brandywine or Mortgage Lifter need stakes or cages installed at planting to avoid root disturbance later.
Harvest begins mid-July for early cultivars, peaking late July through September. Pick fruit when fully colored and slightly soft—taste peaks at peak sugar accumulation, not uniform redness. Watch for cracking after rain; pick slightly underripe if a downpour’s forecast. Succession plant quick-maturing types into early June for extended yields.
