Aubergines, chillies, cucumbers, tomatoes, melons, squashes and sweet peppers can be grafted onto suitable rootstocks.

Grafted vegetable plants can have greater vigour and/or more resistance to soil-borne diseases and pests such as nematodes. This is particularly useful when growing vegetables in the greenhouse border when it may be impractical to use fresh soil every year or practice crop rotation. The advantages are fewer if you usually use containers or growbags each year.

Grafting can be especially valuable for ‘heritage’ cultivars as modern cultivars have some resistance already.

Some grafted plants such as tomatoes can offer earlier fruiting and heavier crops. Commercially, among the main reasons for grafting, are resistance to fungal wilts, encouraging growth and resistance to low temperatures.

Spring is the time to grow rootstocks and scions (the cultivar of vegetable you wish to grow) from seed. As scions and rootstocks grow at different speeds consult suppliers of rootstock seed for exact sowing intervals.

The precise timing depends on the vegetable plant and the conditions you have in which to grow the young plants on. Plants can become leggy if the temperature is too high and the light uneven – such as can happen on a sunny windowsill early in the year.

For outdoor crops, sowing in late March is ideal for crops such as tomatoes, peppers and aubergines, since May to early June is the earliest these warmer climate plants can be moved to outside conditions.

With a heated greenhouse and temperatures of around 15°C (60°F) in which to grow plants on, sowing of tomatoes, for example, could start in mid-February.

Preparation

You will need to grow two batches of plants; the rootstock and the fruiting cultivar (variety). All the well-known cultivars (varieties) will graft. 

1. Sow tomato rootstocks seed a few days earlier than the fruiting cultivar as the seed is somewhat slower to germinate. The germinating temperature should be 17–21°C (65–70°F).
2. High light levels are vital – seedlings can very quickly become leggy – greenhouses are ideal, but windowsills are more challenging.
3. When the seedlings have reached the expanded leaf stage, they are ready for pricking out into individual 7.5cm (3in) pots.
4. They should be grown on in a lower temperature of 13–16°C (56–60°F).

Plants are ready for grafting when they are at least 10cm (4in) tall and have a good stem thickness.

Grafting

Wash hands thoroughly before working on the plants. Choose rootstock and scion plants with similar size and thickness of stem for grafting.

What you will need: A very sharp sterilised blade, such as a scalpel or razor blade (to minimise bruising of the stems), grafting clips* (or Sellotape), clear plastic bag or covered propagator. *Grafting clips are readily available from online suppliers.

Wedge (or cleft) grafting step-by-step (suitable for tomatoes and many other grafted vegetables)

1. Rootstock preparation: Cut off the upper stem of the rootstock and discard, retaining the base. Make a vertical slit up to 1cm (½in) long into the top of the cut-off stem.
2. Scion preparation: Cut off the upper stem of the scion but retain the upper part and discard the base. Cut the base of the scion into a V-shape.
3. Insert the scion base into the slit of the rootstock to complete the wedge graft.
4. Secure the two halves of the wedge graft with a grafting clip. Sellotape could be used instead of a grafting clip to wrap around the union but can be very fiddly.
5. Cover immediately with a clear plastic bag or covered propagator. Place out of direct sunlight and keep at 15-19°C (59°F-63°F).
6. Uncover daily to air plants and check watering. Keep moist but not wet. Note: adventitious roots may form up the stem if conditions are too humid.
7. Once the graft union has calloused and plants are growing strongly (around two to three weeks), remove all covers and clips or Sellotape.

Other grafting techniques

Variations on the wedge grafting technique can also be very successful. These include the saddle graft (inverted V) and the splice graft. See photo gallery for details.

The approach (side-by-side) graft may also be used but takes up more space since the top and bottom of both the rootstock and scion are retained until the graft union has taken.

Rootstocks are divided into two groups:

1. Solanaceae rootstocks for tomatoes, aubergines, sweet and chilli peppers. Two commonly available for the amateur gardener are: tomato F1 Aegis and Estamino F1.
2. Cucurbitaceae rootstocks for cucumbers, melons and watermelons. The most commonly available for the amateur gardener is cucumber ‘Triumph’.

Seed of tomato and cucumber rootstocks is available from Moles Seeds, tel. 01206 213213 and Kings Seeds, tel. 01376 570000.

Grafted vegetable plants are as prone to the usual above ground pests and diseases as their ungrafted counterparts. These include glasshouse whitefly, glasshouse red spider mite, powdery mildew, and tomato and potato blight.

The physiological disorder blossom end rot,  in tomatoes is not significantly affected by grafting. They should, however, be free of soil-borne diseases and pests.