Lemon Boy
Heirloom Tomato in the US

Starting heirloom tomatoes from seed is the way to go, seeing as you rarely find good plug plants. Get your seeds going indoors about 6-8 weeks before your last frost date, using seed trays or small pots filled with good potting mix. Sow them about a quarter inch (6mm) deep. For folks in Zone 5, March or April is your window, same for Zone 6 in February or March. Zone 7 growers can start February or March, and if you're in Zone 8 or 9, January or February is ideal. Keep them warm, around 70-75°F (21-24°C), and give them plenty of light.

Once your seedlings have their first proper leaves, called true leaves, gently prick them out and pot them up into individual 3-4 inch (7-10cm) pots. Keep them growing strong indoors or in a greenhouse. Before planting out, you'll need to harden them off for about a week, gradually getting them used to the outdoors. Plant them in the ground or in large containers once all danger of frost has passed, making sure they're a good 2-3 feet (60-90cm) apart for decent airflow. Strong staking is a must, like I say, these can get big and heavy.