How to Graft Tomatoes

Reader Contribution by The Natural Gardening Company
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Interest in tomato grafting is high among gardeners these days. Grafted plants can be expensive and sources of supply are few. Learning how to do it yourself not only saves money but gives you unlimited options for what varieties you choose to graft. With a little practice, you can become skilled at this worthwhile technique. The benefits of learning include a more productive and disease-resistant tomato crop.

This blog post covers the steps that go into the process commonly called “head grafting,” also known as Japanese grafting, because this is where the technique was first developed. This method allows you to graft your chosen tomato variety (the scion) with rootstock. Rootstock does not produce fruit or foliage but is vigorous and resistant to diseases.

Materials for Grafting Tomatoes

1) Silicone grafting clips (the most popular sizes are 1.5 and 2.0mm);

2) A new, straight edged razor blade;

3) A spray bottle filled with water;

4) Rootstock seeds (we offer a certified organic variety called Estamino that is vigorous and produces well-balanced plants);

5) Scion seeds (heirlooms are popular for grafting because their production can be uneven and they have no disease resistance)

6) A clear plastic bin with lid to hold a tray of grafted plugs.

Plant Your Scion and Rootstock

Your rootstock and scion plugs may grow at varying rates. The first time around, estimate it will take 21 days from seed-planting to stems on each plant that is large enough to graft. Through trial and error, you will find the ideal timing so that the diameter of the scion stem matches the diameter of the rootstock. Your grafts will not all be successful.  It is recommended that you plant 2-3 times as many scion and rootstock plants as you think you will actually need.

The scion is ready when it has 2 or 3 true leaves. When you are ready to begin, prepare a clean working surface with all your materials at hand. Make a mental note of your placement of the scion tray and the rootstock tray and make it a habit to put them in the same spot (one left, one right) whenever you graft — you don’t want to confuse them when you begin cutting. Finally, wash your hands. You don’t want to inadvertently introduce harmful organisms to the cut surfaces.

Remove one rootstock plug from the tray. Look it over carefully and decide where to cut. The cut should
always be just below the cotyledons (the small set of leaves first from the bottom) and at least 1/2″ above the soil line. Use your razor blade to remove the cotyledons. Then cut just below them at an angle between 30 and 45 degrees. After cutting, slide a silicone tube over the cut end of the rootstock. The tube should fit firmly for the best results.

Next, examine your scion plugs and select one with a stem diameter that matches your rootstock. Remove all but the top leaves to reduce transpiration while the graft is healing. Cut at an angle matching the angle of the rootstock, either about 1/3″ above or below the cotyledons. You want an exact fit between the scion and the rootstock.

Align the scion with the rootstock and slide the scion into the tube so the two cut surfaces meet cleanly. The grafting tube should hold the scion and rootstock together firmly.

Move the grafted plant to a clean cell tray. Spray the grafted surface with a fine mist after completing each graft to prevent it from drying out. Keep them in the shade and away from strong wind currents while you proceed with additional grafts.

Healing Grafted Plants

Next comes healing, a critical part of the process. If all goes well, your grafted plants will heal in 4 to 7 days. Ideal conditions for healing are high humidity — upwards of 100% — and steady warmth, with temperatures between 82 and 84 degrees. For the first 24-48 hours, keep the plants in total darkness to prevent transpiration from the scion. Thereafter, they need moderate light roughly equivalent to the intensity of two side-by-side fluorescent tubes.

If you have a greenhouse, these conditions can be met by placing a table beneath a bench and covering it with plastic to retain humidity. Or you can put your grafted plugs in a propagation chamber for the first 48 hours and then beneath a shaded bench and misters for the duration. Home gardeners need a similar arrangement. The easiest solution is a clear plastic storage bin with a lid, the type found at many hardware centers. Choose one large enough to hold your plug tray with grafted seedlings.

While your plants are healing, too much water applied to the soil can create a thin layer of water on the grafted surface. This moisture can create a barrier which interferes with the union between the scion and rootstock. The best way to water during the healing period is to mist the graft union at regular intervals. If you are using a clear storage bin, fill the bottom with about 1/2″ of water before you put your grafted plants inside. This should provide enough moisture and create a high level of humidity inside the container. Make sure the lid on your container has a good seal. If in doubt, tape over any openings. Approximately one week after making your grafts, you should begin to expose your plants to more light and increased airflow by gradually opening the lid. The entire process will take about two weeks.

The grafting tubes will fall away from the graft as your tomato plants grow. To prevent the introduction of disease, do not reuse your grafting tubes.

One final note: When you transplant your grafted plants into your garden, keep the graft line at least 1/2″ above the soil surface to prevent the introduction of disease.

We wish you success!