Your backyard tomatoes should be tall enough to begin staking in May (Zone 5). We highly recommend staking and training tomatoes early, while they are small. If you wait until they flop, you risk breaking the tender stalks.
Keep on pinching the suckers of your heirloom tomato varieties. Suckers are the growth that comes out where the big leaf attaches to the main stem of the plant. By plucking them off, you will increase your chances of bigger fruit and a more bountiful harvest.