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By August 24, 2017 0 Comments Read More →

How to Graft Tomatoes (and other veg)

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Grafting brings the strong points of different varieties to a single plant – disease resistance of hybrid rootstocks and the flavour of heirloom varieties, for example. Mark Abbott-Compton investigates

A BRIEF HISTORY OF GRAFTING

Grafting has been common practice for centuries, but the grafting of vegetables only really took off in the 1920s. The first vegetables to be grafted were watermelon plants, which were grafted onto squash rootstocks to try to increase the yield in the 1900s in an effort to diminish fusarium wilt, which devastated the crop.

Since the 1920s Japan and Korea have led the way, with over 80 per cent of all the vegetables they cultivate being reliant on grafting techniques of one type or another.

Tomato grafting in Europe actually took off in the 1960s, but since the 1990s the grafting of melons, cucumbers and aubergines has also become popular, and today most of the tomatoes, melons and aubergines we buy from our supermarket will have been produced by grafted plants.

COMMERCIAL GROWING

Grafting is used commercially because it increases the amount of crop produced by a single plant. Replacing the rootstock of a plant can change the characteristics of that plant to make it considerably larger, with stronger growth characteristics. This can also be used to great effect if we are trying to grow heirloom or older varieties, which would traditionally have provided much smaller crops than most modern varieties.

Commercially grafted watermelon seedlings.

Another thing that makes grafting commercially viable is that when plants such as cucumbers, melons and tomatoes are young, their roots are very susceptible to thermal stress during early development. Therefore, if we use a rootstock that is more tolerant of hot and cold temperatures, we can actually get a much longer growing season, and it also gives the plant a better ability to withstand stresses.

In a similar way, by using grafting as a technique for our own vegetables, we can gain the advantages of stronger plants and greater resistance to disease and pests.

THE VARIETIES OF VEG YOU CAN GRAFT

The vegetables you can graft successfully are tomatoes, cucumbers, aubergines, peppers, chillies, squashes and melons.

WHY DO WE GRAFT VEGETABLES?

For the very same reasons as the commercial sector: increased crop yield, stronger plants and improved disease resistance. For example, in the case of tomatoes we can take the variety we want to grow and graft it onto a rootstock with far more resistance to soilborne diseases. We don’t even need to use exactly the same species – we can use wild rootstocks crossed with very specific varieties to give us much better disease resistance, and by pairing a hardy rootstock with a slightly less vigorous plant, the advantages of the rootstock are transferred to the whole plant. It does not change the inherent traits of the upper part, though, so the tomato (or aubergine, or whichever other vegetable you are growing) will still be the same size, texture and taste.

Grafted plants can also be grown to crop earlier, and with heavier crops. A grafted aubergine plant, for example, could well start to crop five weeks earlier than a standard non-grafted plant – a huge advantage with regard to productivity.

SELECTING ROOTSTOCKS

For most of us, when we consider grafting – taking a particular variety of plant and grafting it onto the rootstock of another plant, with the below-ground portion of the plant being the rootstock – we would choose the rootstock mainly for its ability to resist infection by soilborne diseases, to increase (or decrease) vigour (as with many fruit trees), or to increase yield. However, recently, it’s also become possible to buy grafted vegetables, both on their own rootstocks, or those of related vegetables, making it easier for the amateur gardener to test the science.

Until quite recently, grafting was an expensive and time-consuming way to produce a crop for small growers, but there are now suppliers selling the seed of varieties grown specifically to supply rootstocks, so you can graft your own plants, and with tomatoes it is actually far easier than you might think.

One point to remember when selecting matching sizes of variety and rootstock is the grafting tube size. Grafting tubes used for the grafting process should be selected according to the size of a plant: too big a tube will not hold the rootstock and the scion stock (the section above the soil) together to create the grafted union, while too small a tube will put too great a pressure on the fragile join, and may even deform the union. 

THE ‘TOMTATO

Recently, there has been the development of a plant referred to as a ‘tomtato’, which marries tomatoes and potatoes, giving you a crop of both from one single plant. A lot of people were surprised that it worked, but both come from the same plant family, and what’s interesting is that the potato is the tuber section of the plant, with the tomato as the fruiting section above ground, so grafting them together is sound science, and does work. Interestingly, you don’t get a large crop of either, but it is fantastic as an experiment, and also really interesting for children to show them the familial relationship between plants.

Tomtato.

Recently, the tomtato has been superseded in newsworthiness by a plant sometimes referred to as ‘egg and chips’, which consists of an aubergine grafted onto a potato – both again from the same family.

GRAFTING MELONS AND CUCUMBERS

The grafting of melons or cucumbers is harder to carry out in the amateur environment because it needs to be done when the seedlings are newly germinated. Both varieties are normally grafted onto squash rootstock, which is much stronger growing and more resistant to disease, but both the squash rootstock and the melon or cucumber develop hollow stems very early after germination – technically referred to as ‘hypocotyls’. You need to graft both plants together before the stems develop a large internal hollow section, which expands as the seedlings grow, reducing the contact area for the graft to take. Consequently, at the stage you are grafting you are dealing with very tiny seedlings with all of their inherent weaknesses.

Grafted cucumber plants.

Commercially, a more technical type of graft, called a ‘Hole Insertion Graft’, is often used because it can be more successful with hollow-stemmed plants, but it is a much more difficult challenge for the keen amateur to undertake.

GRAFTING TOMATOES STEP-BY-STEP

You will need to buy some grafting tube or grafting clips. These are now readily available in many good horticultural stores, but if you are not able to find any I would recommend a quick search online. They are quite inexpensive to buy.

The first thing you will need to do in order to graft tomatoes is to sow your actual chosen varieties about 4–5 weeks before you intend to graft them. Hybrid rootstock varieties may germinate slower, so they will normally need sowing 5–7 days before any heirloom varieties. Consequently, if you are going to be grafting using hybrid rootstocks – the most likely option – you will need to work out your optimum sowing times. It is a good idea to plant a few test seeds of each tomato (both rootstock and scion stock) earlier in the year to determine just how long the germination period is for each, if you are unsure. Both Submarinine F1 and Estamino F1 are strong and readily available tomato rootstocks.

Donor plants (scion stock).

A rootstock plant.

When the seedling has reached the two true leaf stage, it’s time to graft, but you can let your plants grow to 15–20cm tall, when they will be much easier to work with. Remove one plant at a time from the tray. It’s a good idea to keep the rootstock on the left and the scion stock on the right when working, so you always know for sure which is which.

Line up the rootstock and the variety next to each other and look for the point on the stem with the best diameter match (1.5mm is ideal) below the seed-leaf – technically called a ‘cotyledon’. Choose a grafting clip or tube to suit the diameter of the seedlings’ stems.

Use a sterile razor blade at an angle of about 45° to cut through each seedling stem, ensuring that the cut is as true as possible across both plants. Place a grafting tube or clip halfway down on top of the cut-end of the rootstock, then insert the scion, matching up the 45° cuts on the stems of both seedlings into the grafting tube or clip. The cut surface of the scion must align perfectly with that of the rootstock so that the plant tissue can easily fuse together properly, forming a strong union for both water and nutrient uptake.

  • Cutting a donor plant.
  • Donor plants.
  • A rootstock plant.
  • The matching grafting cuts.
  • Donor and rootstock with clip attached.

 

Finally, plant the grafted tomato into a 7.5cm pot using two-thirds multi-purpose compost and one-third perlite.

Move the grafted plants to a closed propagator and keep the humidity high, misting twice a day with water to prevent desiccation. Healing should take up to 7 days. There is no need to remove the tubes, as they will fall off naturally as the stems grow.

A grafted plant with the joint showing at the base of the stem.

POTENTIAL PROBLEMS

If you are going to use grafted tomatoes, do not plant them quite as deeply as is commonly recommended when planting out. Planting below the rootstock will allow roots to form from the original plant used as the scion stock, so it’s important that this section remains above soil level.

If you are considering buying grafted plants, you will find they are usually quite expensive – sometimes as much as five times the cost of a standard non-grafted tomato. You are paying not only for the growing time, but also for the time spent grafting, which is undeniably time-consuming, so perhaps this in itself is a good incentive to try doing some grafting for yourself!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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