How to Grow Hardy Northwest Tomato Rootstock

Purchase your rootstock tomato seeds from a reputable source early enough to sow your tomatoes in early March, eight weeks before the planting date. Store them in a cool, dry place.

Mix water into the seed starter mix until it is damp, but not wet, and fill the pots. Sow one seed per pot five to seven days prior to the sowing date for plants to be grafted to the rootstock by cleft grafting and one to two days prior for tube grafting. Having the plants in individual pots eliminates the stress of transplanting them before grafting. Keep the soil evenly moist but not wet.

Use heat tape or a heating mat to hasten germination if desired. If the air temperature if 60 degrees F or over, no bottom heat is needed.

Place the pots into a full-sun location once the seeds have sprouted. A southern window is ideal. Turn the plants frequently to prevent stretching. Provide adequate air circulation to prevent the death of seedlings from fungal disease, known as dampening off.

Fertilize the rootstock plants with a one-quarter strength solution of liquid tomato fertilizer when they get their first set of true leaves. For cleft grafting, plants should have four to five sets of true leaves. For tube grafting, since the cut is made below the seed leaves, the size of the plants is only limited by the size you can comfortably work with. People with small hands and nimble fingers will be able to graft much smaller plants with as few as one or two sets of true leaves.