Grafting Tomatoes: Splice Grafting Step by Step

A grafted tomato looks like any other at first glance. The difference sits two fingers above the soil: a small bulge, the scar where two plants have grown together. Below, a wild-tomato cross with a root system that rarely falls ill and still pulls nutrients from tired soil. Above, your favourite variety, which you grow for its flavour and not for its toughness. It sounds like nursery craft, but it works at the kitchen table. Anyone who has ever raised seedlings on the windowsill already has everything they need.

What grafting actually means

Grafting combines the strengths of two plants. The rootstock, botanically often a cross of Solanum lycopersicum and the wild Solanum habrochaites, brings vigour and resistance to soil-borne diseases. Its fruit would be too small and bland for you. The scion, the upper part, is your chosen variety: an aromatic beefsteak, an old heirloom, a sweet cocktail tomato. Both are separated at the seedling stage and rejoined crosswise. What grows together then shares its vascular pathways: the root sends water and mineral salts up, the leaves send sugar down.

The principle is ancient and comes from fruit growing. With tomatoes it was long used only in professional operations, because there the same greenhouse soils are planted for decades and fungi such as Verticillium or Fusarium accumulate. For the home garden the technique has only become interesting since ready-made rootstock varieties are available as seed and cheap silicone clips hold the join stable.

Who it pays off for and who it does not

Grafting is not a must. In fresh, healthy garden soil a good variety brings a generous harvest even without a rootstock. In certain settings, though, the effort clearly pays off.

It makes little sense if you plant in a different outdoor spot every year and grow tough, modern varieties anyway. Then you put work into something the soil does for free. And honestly: anyone growing tomatoes for the first time should master raising seedlings reliably before reaching for the scalpel.

The most common beginner mistake does not happen at the cut but already at sowing. Rootstock and scion must be equally thick at grafting time. Because many rootstock varieties germinate a little more slowly, you sow them three to five days before the chosen variety. Note down both sowing dates. If you sow both on the same day, you often end up later with one thin and one thick stem, and those do not fit together cleanly.

The right timing

Grafting is done at a very young stage, when the seedlings have two to four true leaves and the stem is about pencil-thick. In practice, depending on sowing, that falls in CW 8 to 12, so late February to late March. That fits well with the usual sowing date for greenhouse tomatoes. More important than the calendar date is the stem thickness: too thin and the cut tears out, too thick and it heals slowly and the clip holds poorly.

Splice grafting step by step

Splice grafting, sometimes called top grafting, is the most common method for tomatoes. You cut both plants with an angled cut and set the head of the scion onto the foot of the rootstock. A silicone clip holds the cut surfaces together until they knit. Work in a clean spot, wash your hands, and use a fresh, sharp blade.

1. Prepare your tools

   Scalpel or a new razor blade, grafting clips with 1.5 to 2 mm inner width, a spray bottle of water, and a clear dome or a large clear bag. Wipe the blade briefly with alcohol.

2. Cut the rootstock

   Cut the rootstock just above the seed leaves with a smooth, angled cut at around 45 degrees. The root with a short stem stays in the pot, the upper part is discarded.

3. Cut the scion

   Cut your chosen variety at the same angle. This time you keep the upper part with the leaves. Make sure both cut surfaces are the same size and meet flush.

4. Join them

   Set the scion onto the rootstock so the cut surfaces fully overlap. Slide the silicone clip over the join. It holds both parts in place without crushing them.

5. Mist immediately

   Mist the freshly grafted plant finely with water and place it under the dome. From now on only moist air and shade matter.

Do not despair if the first attempts fail. Simply set up more plants than you need in the end. A rate of two successes out of three attempts is completely normal at first, and with a little practice you will soon manage almost all of them.

The healing phase decides success

Now begins the part many underestimate. The cut surfaces must knit before the upper plant loses too much water. For that you need a kind of mini greenhouse: high humidity close to saturation, temperatures around 22 to 25 degrees, and above all shade. Direct sun would wilt the not-yet-supplied variety within hours.

Keep the plants fully closed and shaded for three days. From day four you open the dome a little more each day and carefully let light in. After five to seven days the scion stands upright on its own, without wilting, when you take off the dome. That is the sign that the vascular pathways are reconnected. Only then do you slowly get the plant used to normal conditions.

Once the join has knit, you grow the plant on like any other young tomato: bright, moved somewhere cooler, hardened off slowly. One point stays important for the whole gardening year, though. The graft union must always stay above the soil. If you plant the tomato deeper, the scion forms its own roots and the entire advantage of the tough rootstock is gone. So set it shallower than ungrafted tomatoes and keep the scar exposed.

Combining rootstock and variety wisely

You buy the rootstock as seed of varieties bred specifically for it. Common and widely available are vigorous hybrids bred for disease resistance and vigour. They bear no fruit worth mentioning, and that is deliberate: all the strength should go into the root system and the scion set on top.

Almost any variety you like works as a scion. The effort pays off especially with weak-growing but aromatic varieties that often struggle on their own. If you are unsure which variety suits your site, the overview of variety types from cocktail to beefsteak helps. A grafted plant grows more vigorously than usual, so give it more room and remove the side shoots consistently, or the foliage turns into a jungle.

A word on disease prevention: grafting strengthens the root but does not make the leaves immune. Against the dreaded late blight only a dry leaf canopy, an airy position, and a rain cover still help. The rootstock protects above all against what comes from the soil.

Frequently asked questions