Grafting Tomatoes: The Secret to Unlocking Amazing Tomatoes

Tomato grafting is a practice that many gardeners use to improve their tomato yields. This secret has been practiced for decades and is fairly easy to do. In this article, gardening expert Jenna Rich shares everything you need to know about grafting tomatoes this season.

tomato grafting

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The first time I heard about grafting tomatoes, it seemed like something only a scientist could pull off. But the more I researched the potential benefits and saw other farmers were doing it, it seemed silly not to give it a shot!

While grafting is most commonly used in orchards, grafting vegetable plants such as tomatoes, cucumbers, and eggplants is taking hold in the farming and gardening world, and it’s exciting.

Once you see the results from a grafted tomato plot, you’ll never return to the traditional way of growing tomatoes. Before you start, it’s important to know the basics. Continue to learn exactly what grafting is and why it’s the secret to unlocking amazing tomato plants in your garden this season!

What is Grafting?

Close-up of grafted tomato seedlings with wooden supports in white planting bags. Seedlings have vertical slightly hairy stems and oval green leaves. A special clip is fixed at the grafting site.
Grafting combines plants to benefit from disease resistance and vigor, with the desired tomato variety.

Grafting is the act of splicing together two different plants of the same species. This allows the gardener to reap the benefits of the rootstock variety.

The rootstock, or stock, is bred for disease resistance and vigor but not necessarily for fruit production. The scion is the tomato variety you’d like the fruit of, which is grafted to the rootstock.

While it does come with some additional time and cost, the benefits outweigh the trouble that goes into the process of grafting.

Why You Should Graft Your Tomatoes

Close-up of a grafted and trimmed tomato seedling in a garden, planted in coconut fiber in sandy soil. The seedling has a pale green upright stem, slightly hairy, with compound leaves that consist of oval, pale green, large-toothed leaflets. A translucent plastic clip is attached at the grafting site.
Grafting combines rootstock and scion to enhance tomato production and reduce disease pressure.

We all have our favorite heirloom tomatoes. And we also know that heirlooms are prone to disease and pest pressure. They aren’t as accustomed to the changing climate and do not produce nearly as much as modern-day hybrids.

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Grafting has many benefits, including increased tomato yield.

In a nutshell, grafting combines the characteristics of the rootstock with the delicious tomato of the scion. This results in higher production, lower disease pressure, and a longer season of enjoying your favorite tomatoes.

Farmer-to-farmer tip: If you are growing tomatoes to sell, grafted tomatoes have many benefits.

  • The ability to transplant sooner because grafted tomatoes tend to handle cooler temperature soil
  • Faster growth
  • You’ll get mature fruit earlier
  • Plants have more trusses full of tomatoes
  • The ability to withstand long, hot summers, leading to a longer season
  • Increased profits and happy customers

The biggest problem you might have is finding more outlets at which to sell your tomatoes! Trust me. You’re going to have a lot more!

A Brief History of Grafting

Close-up of a grafted and pruned tomato seedling in a garden, planted in coconut fiber in soil with sand next to which a black hose for drip irrigation is held. The seedling has pale green upright stems, with compound pinnate leaves that consist of oval pale green, slightly serrated leaflets. At the bottom of the stem, at the grafting site, a translucent plastic clip is attached.
Grafting has a long history, from ancient farmers grafting gourd plants to modern examples.

The first record of grafting is thought to have been back in 500 AD when farmers grafted together several different gourd plants because they wanted larger fruit and a greater root system. That’s farmer ingenuity right there.

Then in the 1920s in Japan, grafting was reintroduced to farmers. It was viewed as a revolutionary way to produce vegetables when an article was published about a man named Ukichi Takenaka, who grafted a watermelon onto a pumpkin. By doing so, he successfully overcame the dreaded Fusarium wilt.

More recently, you may have heard of apple trees being grafted or the ever-popular “fruit salad trees,” where several different types of fruits are grafted together on a single rootstock.

Pre-Grafting

Close-up of short cut tomato stems with plastic grafting tubes attached, in starter seed trays. Stems are green-pink, slightly hairy. Trays are plastic, with deep rounded cells filled with moist soil.
There are three common tomato grafting methods: splice graft, side graft, and cleft graft, that require practice.

There are three widely accepted ways to graft tomatoes that I will discuss here. The splice graft, the side graft, and the cleft graft. They can all seem a bit scary and strange. But just like anything else, it just takes some practice to get used to it. Based on my experience, you’ll get better with every cut

What you’ll need to get started:

  • A miter-cut grafting knife or traditional razor blades
  • Rootstock seeds
  • Your favorite tomato seeds (that are about to get even better). They will be referred to as scions.
  • Different-sized silicone clips and/or side graft spring clips
  • Support stakes
  • Misting spray bottle
  • Humidity domes or a healing chamber

Start your tomato seeds as you usually would, noting that rootstock varieties typically have inconsistent germination and growth. To avoid confusion, we start our scion varieties in 50-cell trays and the rootstock in individual 2-inch pots.

This is so that when it’s time to cut and clip, there is no way to mix up the two varieties, and the tray of 2-inch pots can go straight into the healing chamber.

At about the 3-week mark, compare the size of the rootstock and scion tomatoes. You want the stems to be as close in diameter as possible for a successful graft. Remember that you can do your grafting in more than one session. The growth of your scions will catch up to the rootstock.

Once you have enough tomatoes that match up in size, grab your supplies and healthy tomato plants. Preferably start in a mild-temperature workspace out of the sun when getting started.

Splice Grafting

Tomato seedling grafting technology close-up. The tomato seedling has two stems attached with a grafting clip, and two oval leaves.
Make angled cuts on the rootstock and scion, match similar stem sizes, secure with a clip, and add support if needed.

Notice the grating knife features different stem notches. Find a comfortable grasp and line the stem of your rootstock with one of the stem notches.

The way this tool is built makes it pretty foolproof. Just make sure you hold the stem in the same notch each time. The design holds the razor blade at the correct angle (about 45°) each time you cut. This way, your stems line up with one another before grafting.

At this time, go ahead and snip the tops off of the rootstock above the cotyledons (those small leaves on the lowest part of the plant and the first to emerge) and discard them. Find a clip size that works for each of the rootstocks and clip it right on.

These vary in size, ranging from 1.5-3.5 mm. It’s a good idea to have several sizes to choose from. Now, look around for a similarly sized scion top and snip it above the cotyledons. Use the same angle you cut the rootstock. The angle matching up as close to perfect as possible is very important for a seamless graft.

Farmer-to-farmer tip: If you are growing on a larger scale and are doing several trays of these at a time, you can do all the cuts at the same time. You might expect that all of the rootstocks will die as soon as you cut their tops off. But I promise you, they won’t. Work swiftly and confidently. You have some time. It’s better to take your time than to rush and make mistakes.

Pro tip: If the stems aren’t exactly the same size, always pair a larger rootstock with a smaller scion. The reason is if you do the opposite, the plant may become top-heavy and fall over. However, if it’s too small, there may not be enough surface area to “take,” so try to get the stems as close in diameter as possible.

Now that you have your scion top and rootstock bottom cut, loosen the clip and lower the scion top into place, lining up the angled cuts until they are snugly touching.

Now tighten the clip back around the two stem pieces. Make sure the cuts are in the middle of the clip for stability. Add a support stake if necessary.

Side or Tongue Grafting

Close-up of a woman's hands making an incision with a blade on the stem of a plant for grafting, against the backdrop of a white bowl with blue clips and a starter black round-mesh seed tray. The stem is upright, green, slightly hairy, with oval green leaves.
For side grafting, use a new razor blade to avoid contamination.

Side grafting is done with a regular, sharp razor blade. Be sure to use a brand-new razor blade each time you are grafting to avoid any disease contamination. For this method, you will still cut off the top of the rootstock to begin. Then identify a similarly stem-sized scion.

Make an upward cut near the top of the rootstock stem about ⅔ of the way through the stem. Make a similarly placed downward cut in the scion and fit the cuts together. Using a side graft spring clip that fits both stems, secure them together. Then put them into a pot together and add a little soil.

At this point, they are ready to be covered with a humidity dome or put into a healing chamber for 2-3 days. After this time, remove the plant (s) and make only a partial cut in the scion stem so the plant can acclimate to using the rootstock roots.

If you make a full cut right away, the plant may be shocked. Put it back into the healing area for 2 more days. Then you can cut the rest of the scion stem off. A day or two more in the healing area is advised.

Cleft or Top-wedge Grafting

Close-up of female hands grafting a plant using top-wedge grafting method. A plant in a black planting bag, has an upright green stem with a notch, into which the stem of another similar plant is inserted for grafting.
Top-wedge grafting requires less humidity for healing compared to other methods.

As with the other two types, start by cutting off the top of the rootstock. Then, using a new, sharp razor blade, slice a small slit down the center of the rootstock stem vertically, about .5 cm.

Then, cut your similarly stem-sized scion top into a wedge the same length as the slit you just made in the rootstock. Imagine it to be sort of like the shape of a flathead screwdriver. Place the scion “wedge” into the slit and clip the graft area.

The main advantage of this method includes not needing such high humidity to heal the graft. Some sort of healing area is still advised.

Post Graft Care and Healing

Close-up of a garden bed with growing grafted tomato seedlings. The bed has a layer of coconut mulch and a long black hose with holes for drip irrigation. The tomato plant has upright stems and compound leaves consisting of oval, large-toothed, pale green leaflets. Translucent plastic clips are attached to the bottom of the stem at the grafting site.
Maintaining proper humidity levels is crucial for graft healing.

Proper humidity levels are vital after grafting takes place. Humidity helps the graft wound heal and ideally remains around 90-95%, except if you cleft graft.

If you are doing this on a fairly small scale, humidity domes work just fine. You should lightly mist and then cover the tomatoes immediately after their “surgery” and then store them in a warm environment out of the sun. This could be under a greenhouse table, in a home closet, or in a healing chamber.

Farmer-to-farmer tip: A healing chamber will be crucial if you are grafting several trays of tomatoes at a time. This will allow you to control the humidity and keep all your plants in the same environment.

During this time, the plants are simply healing, not growing. Keep this in mind when planning for your season. You may want to start your tomato seeds earlier than usual to account for the time the plants will need to heal. After 2-3 days in a healing chamber or under humidity domes, you should crack the door or dome to decrease the humidity.

You should also think about introducing some light. For us, this means simply cracking the door of our healing chamber a bit more each day. This allows the plants to acclimate slowly. Eventually, they receive a full day out of the healing chamber under indirect, artificial light.

Later still, we bring them out to our greenhouse, introducing them to the real sun with the protection of shade cloth, then eventually, direct sunlight.

If at any time during a new stage, as part of the post-graft process, your plants start to wilt or look unhealthy, they may not be ready and should be placed back into the previous stage. Just keep a close eye on them throughout the process.

This may sound like an extra amount of care, and perhaps it is. But imagine you just had surgery, and you were given a bandaid and sent back to work the next day. I promise if you baby these plants just a little bit after the grafting process, which in the grand scheme of things is about 4 weeks, you will be blown away by the results.

Note that the silicone clips will work their way off as the stems grow. Retrieve these all and disinfect them before using them again. Bottom water or misting will be best for a while as the tops continue to heal.

A Few Important Notes

Close-up of hands in white gloves grafting a tomato plant. The tomato plant is small, has a thin green stem with a pair of tiny oval green leaves attached to the stem of another tomato with a translucent clip.
When grafting, be cautious of suckers produced by the rootstock below the graft line.

When using any grafting technique, if you cut above the rootstock cotyledons, remember that you will need to check for early suckers that the rootstock is sending out. Since these would be below the graft line, the sucker will produce rootstock fruit you don’t want.

To avoid this issue entirely, you can cut below the rootstock cotyledons. Your plant will be a bit shorter, and it may be a little tougher to graft, but there won’t be any possibility of suckers as the rootstock will have no leaves of its own.

Also, remember those adventitious roots I mentioned earlier? Your scions might start forming lots of these at the graft point. This is normal. Just snip them off or allow them to dry out completely before planting out.

Grafting tape may be used to aid in the healing process.

Transplanting Grafted Tomatoes

Close-up of a gardener's hands in gray gloves transplanting a grafted tomato plant in the garden. The soil is moist and black. The tomato seedling has vertical stems with pinnately compound leaves consisting of oval bright green leaflets with serrated edges. A garden shovel is inserted on the soil nearby.
After successfully grafting and healing tomato plants, the crucial part is transplanting them carefully.

If you have successfully grafted and healed tomato plants, keep reading because the most crucial part of now having a successful season with these tomato plants is actually transplanting.

Any solanaceous vegetable plant, which tomatoes fall in the category of, forms small, bristly roots along their stem, called adventitious roots. If you hold a sizeable tomato plant up to the light, you can see little hair-like fuzz. These are the roots.

These roots are formed from non-root material, and the term adventitious means they have the ability to become a root if they come into contact with soil. Pretty cool!

Now, if you think about being told to bury tomatoes (un-grafted plants, that is) deep beneath the soil when transplanting for a strong plant base, this may make more sense now. The adventitious roots all along the stem will shoot out into the soil, becoming real roots. This adds strength and stabilization to the tomato plant, setting it up for success after transplanting.

I mention all of this because in the case of grafted tomatoes, the graft line must not be buried beneath the soil surface. If this happens, the whole process of grafting will have been a waste. This is because the scion variety stem will send out roots, transitioning back into the scion variety and losing the effects of the graft altogether.

So when transplanting grafted tomatoes, dig your hole a little more shallow than you usually would. After adding any amendments or compost to your hole, tuck your tomato in, and keep that graft line well above the soil surface. Give the plants support if needed; from here on out, they can be treated as usual.

Frequently Asked Questions

It’s ok. Just snip them off as soon as you can before they start sending energy to those parts and producing fruit. To avoid this in the future, cut your rootstock below the cotyledons so there is no chance of it sending out suckers. It may be a little tougher to cut the stem, so just take caution.

It sounds like maybe your rootstock size is larger than the scion tops. Find a scion with a similarly sized stem for better results.

If you see some limp leaves and slimy centers of tomato plants, you may have watered too much. Remember, the humidity dome holds humidity in very well, and as long as you keep your humidity level high enough in a healing chamber, you shouldn’t have to water much. Maybe just a spritz every few days. If the soil feels damp, the plants are fine.

After about a week or so, you can sacrifice one of your plants by taking it out of the humid environment and seeing how it does. It worked if the top doesn’t fall off and the plant doesn’t go limp! Now you can slowly introduce your plants to the real world.

Once they are further along, you will see a clearly healed graft line. You should be able to gently tug on the top of your plant with no problem when grafts are successful.

Final Thoughts

Grafting tomatoes may seem scary, but once you try it out a few times and see the drastic results, you won’t want to go back. Although it is more costly to graft and it takes time, energy, and patience, I bet you’ll be thrilled with the increased production, decreased disease pressure, and overall performance.

Before you know it, friends and neighbors will be asking you what your tomato-growing secret is when you’re swimming in tomatoes. Happy grafting, you got this!

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