What grafted tomatoes are and why to plant them

A grafted tomato is two plants joined together: a disease-resistant rootstock (the root system) fused to a fruiting variety you want to grow (the top part). The graft point is the visible knot or scar where they meet, usually a few inches above the soil line. You plant it the same way you would a regular tomato seedling, but the graft union itself must stay above ground — burying it defeats the whole purpose.

Grafted tomatoes cost more than standard seedlings because they resist soil diseases like fusarium and verticillium wilt, which can kill an ordinary plant mid-season. If your garden has had tomato disease problems before, or if you are planting in the same bed year after year, a grafted variety can be the difference between a harvest and a loss. The rootstock does the heavy lifting underground while the top produces the tomato variety you actually want to eat.

Key Takeaways

  • The graft union (the knot where the two plants join) must stay above the soil surface when you plant, or the scion will root and you lose the disease resistance.
  • Harden off grafted seedlings for 7 to 10 days before planting outdoors, because they are often grown in controlled nursery conditions and need gradual exposure to sun and wind.
  • Plant grafted tomatoes at the same depth as a regular seedling — with the lowest leaves just above soil level — but never bury the graft point itself.
  • Support the graft union with a stake or cage from planting day onward, because the joint is structurally weaker than a natural stem and can snap under the weight of fruit.
  • Pinch off any shoots that emerge below the graft union, because they come from the rootstock and will not produce the fruit variety you want.

Preparing the planting site and soil

Grafted tomatoes need the same conditions as any tomato: full sun (at least 6 to 8 hours daily), well-draining soil, and protection from strong wind. The graft union is the weak point, so wind matters more than it does for standard plants. If your garden is exposed, plan to stake or cage the plant when ready.

Amend your soil with compost or aged manure before planting. Grafted tomatoes are not more or less hungry than regular ones, but they do benefit from consistent nutrition because the rootstock is working hard to deliver water and nutrients to a heavy-fruiting top. Mix 2 to 3 inches of compost into the top 8 to 10 inches of soil, or dig a planting hole and backfill with a 50/50 mix of native soil and compost.

If your garden has a history of soil-borne disease, that is exactly why you chose a grafted plant. You do not need to sterilize the soil or change your routine — the rootstock will handle what would have killed an ordinary tomato. However, do not plant a grafted tomato in the same spot where a diseased tomato died the previous year if you can avoid it. Rotate to a different bed if one is available.

Hardening off before planting outdoors

Grafted seedlings arrive from the nursery in a controlled greenhouse environment. They have not experienced outdoor sun, wind, or temperature swings. If you plant them directly outside, they will wilt, sunburn, or stop growing for weeks while they adjust. Hardening off — gradually exposing them to outdoor conditions — takes 7 to 10 days and is not optional.

Start by placing the seedling in a sheltered spot outdoors (against a wall, under an eave, or in dappled shade) for 2 to 3 hours on day one. Each day, increase the time outdoors and the amount of direct sun by an hour or two. By day 7 or 8, the plant should be outside all day. On day 9 or 10, leave it out overnight if nighttime temperatures are above 50°F. Once it has spent a full 24 hours outdoors without wilting, it is ready to plant in the ground.

If you skip this step or rush it, the plant will survive, but it will sit stunted for 3 to 4 weeks while it toughens up. That delay pushes your harvest back by the same amount. The 10 days of hardening off pays for itself in earlier fruit.

Planting depth and positioning the graft union

The graft union must stay above the soil surface. This is the single most important rule. If you bury it, the scion (the fruiting variety on top) will root into the soil and bypass the rootstock entirely. You lose the disease resistance, and you have wasted money on a grafted plant.

Plant the seedling so that the lowest true leaves are just above the soil line, the same way you would plant a regular tomato. The graft union — the visible knot or scar — should be 1 to 2 inches above the soil surface. If the seedling is tall and leggy, you can bury the stem up to the lowest leaves (tomatoes will root along a buried stem), but stop before the graft point.

Dig a hole slightly wider and deeper than the root ball. Set the seedling in place, backfill with soil, and water thoroughly to settle the soil and eliminate air pockets. The graft union should be clearly visible above the finished soil level. If you are unsure where it is, ask the nursery before you leave — a small photo or marking on the pot usually shows it.

Staking and supporting the graft union

The graft union is a scar, not a natural joint. It is structurally weaker than the rest of the stem and cannot support the weight of a mature tomato plant without help. Install a stake, cage, or trellis on planting day, before the plant is established. Waiting until later risks damaging the roots when you drive a stake into the ground.

Use a sturdy stake (at least 1 inch diameter, 5 to 6 feet tall) or a heavy cage. As the plant grows, tie the stem loosely to the support with soft ties (cloth strips, plant tape, or velcro straps work well). Tie below the graft union and again every 12 to 18 inches up the stem. The goal is to keep the graft point from flexing or bending in the wind.

Some growers use a short stake (2 to 3 feet) placed directly under the graft union to prop it up, then a taller stake or string trellis for the rest of the plant. This double-support method works well if you have the materials. The important thing is that the graft union itself does not move.

Removing rootstock shoots and ongoing care

As the plant grows, watch for shoots emerging from the stem below the graft union. These come from the rootstock, not the scion. They will never produce the tomato variety you want — they will produce whatever the rootstock variety is, which is usually a small, disease-resistant type bred for root strength, not fruit quality. Pinch or cut these off as soon as you see them.

Rootstock shoots are straightforward to spot because they look different from the main plant: smaller leaves, thinner stems, and a different growth pattern. Remove them at the base with a clean pinch or pruner. Do this every week or two during the growing season. If you let them grow, they will compete with the scion for water and nutrients and reduce your harvest.

Otherwise, care for a grafted tomato exactly as you would a standard plant: water deeply and consistently (1 to 2 inches per week), fertilize every 2 to 3 weeks once flowering starts, and prune suckers (shoots between the main stem and branches) on indeterminate varieties. The graft does not change watering, feeding, or pruning schedules — it only changes disease resistance and support needs.

Troubleshooting common grafted tomato problems

If the plant wilts despite adequate water, check the graft union for cracks or damage. A damaged graft can fail mid-season, cutting off water flow to the top. If the union looks intact but the plant is still wilting, the problem is likely soil moisture or disease in the rootstock itself (rare, but possible). Dig down and feel the soil 6 inches deep — it should be moist but not waterlogged.

If the plant grows slowly or produces few flowers, it may not have hardened off properly, or it may be in too much shade. Grafted tomatoes need the same light as regular ones. Move it if possible, or wait — a slow start often catches up by mid-summer. If growth remains poor and the graft union looks healthy, the problem is likely soil fertility or inconsistent watering, not the graft itself.

If you see shoots below the graft union that you missed, remove them when ready. The longer they grow, the harder they are to remove cleanly. If the graft union itself cracks or splits, the plant is likely finished — a broken graft cannot be repaired in the field. Stake it heavily and hope, but plan to replace it next season.

Frequently Asked Questions

Can I bury the graft union if my seedling is too tall?

No. You can bury the stem up to the lowest leaves, but never the graft union itself. If the seedling is very tall and leggy, it is better to plant it at an angle (tilted in the hole) so the graft stays above soil, or to return it to the nursery for a shorter one. Burying the graft defeats the entire purpose of buying a grafted plant.

What happens if I forget to remove rootstock shoots?

They will grow and compete with the fruiting variety for water and nutrients, reducing your harvest. Remove them as soon as you notice them. If you miss them for several weeks, the plant will still produce fruit, but less of it. Pinch them off at the base and the plant will redirect energy back to the main stem.

Do grafted tomatoes need different fertilizer than regular tomatoes?

No. Use the same fertilizer schedule and amounts you would for a standard tomato. Grafted plants are not heavier feeders, but they do benefit from consistent nutrition because the rootstock is working hard to deliver water and nutrients to the fruiting top. Avoid over-fertilizing, which can cause excessive foliage and fewer flowers.

Can I save seeds from a grafted tomato?

Yes, but the seeds will grow into the scion variety, not a grafted plant. The rootstock is not involved in seed production. If you save seeds and plant them next year, you will get a standard tomato plant without disease resistance. That is fine if you want to — just know that the offspring will not have the same advantages as the parent.

How long does a grafted tomato plant live?

One season, like any tomato. Tomatoes are annuals in most climates. At the end of the season, pull the plant and compost it. The graft does not extend the plant's lifespan — it only improves disease resistance during that one growing season. Next year, buy a new grafted seedling if you want the same benefits.