Tomato Grafting: How to Grow Disease-Resistant Heirloom Tomatoes

Last Updated on July 3, 2019 by Aaron von Frank

Tomato grafting is a relatively advanced gardening technique used to produce extremely disease-resistant tomatoes — and make heirloom tomatoes disease-resistant. Tomato grafting can be essential for gardeners and farmers growing tomatoes in hot, humid climates (like the southeast US) where tomato diseases proliferate. 

Want to grow disease-resistant heirloom tomatoes? Try tomato grafting! 

We live in the southeast, USA. In case you’ve never been here, it’s so hot and humid in the summer, that you have to take a hot shower at night to cool and dry off. (Not really, but you get the point.)   

Unfortunately, soils in our region have also been ravaged by years of unsustainable farming and soil management practices.

This is not a healthy ecosystem with living soil. It’s a broken one courtesy of unsustainable farming practices.

The combination of hot, humid weather conditions + poor soil + intensive monoculture farming practices means our region is the ideal breeding ground for every tomato disease known to mankind. Some of the worst tomato diseases are fusarium wilt and verticillium wilt which can turn seemingly healthy tomato plants into limp heaps seemingly overnight. 

What are heirloom tomatoes and why should you grow them? 

Think of heirloom tomatoes as “antique” varieties of tomatoes. Some of them date back hundreds of years, and have cultural significance to their regions of origin.  

Heirloom tomatoes are renown for their rich, distinct flavors and their unique shapes, colors, and sizes. People who’ve eaten their first sun-ripened heirloom tomato directly off of a plant at Tyrant Farms have remarked that they “never knew tomatoes could taste this good.”

An heirloom tomato snack (black prince and persimmon tomatoes with thai and purple basil) at Tyrant Farms. Yum!

The older heirloom tomato varieties might have incredible flavor, but they are nearly impossible to grow year after year in the same spots in the southeast because tomato plant pathogens build up in the soil. That’s why many gardeners and farmers in our area only grow hybrid tomatoes.   

What are hybrid tomatoes?  

Hybrid tomatoes are genetically stabilized crosses of other tomato varieties. They’re typically very vigorous and productive. Many hybrids have also been bred to be highly resistant to a wide range of tomato diseases. 

Chances are, nearly every tomato in your local grocery store is a hybrid tomato. 

In this fascinating NPR interview, Barry Estabrook, the author of Tomatoland, outlines some unfortunate truths about many of today’s tomatoes. Namely, the most commonly grown hybrid varieties were bred to:

1. be disease-resistant,
2. produce indestructible fruit that lasts virtually forever, and
3. be visually appealing (big, round and red).

Notice that “better flavor” was not included in that top-3 list of priorities. Nor was “more nutritious.”   

What if you could somehow get the flavor and nutrition of heirloom tomatoes with the disease-resistance and root vigor of hybrid tomatoes. We’ve got good news: you can!

 

 

 

 

 

 

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Black beauty tomatoes. We’ve had some that get almost uniformly dark black/purple, but these beauties have some gorgeous red flame action going on below those purple shoulders. All the best flavor notes you could want in an heirloom tomato with some extra anthocyanin for your health. #blackbeautytomatoes #heirloomseeds #growjourney #heirloomtomatoes

A post shared by Tyrant Farms (@tyrantfarms) on Jul 27, 2018 at 8:21am PDT

Tomato grafting to grow disease-resistant heirloom tomatoes on hybrid rootstock

Plant grafting is a process wherein a cutting/branch of a desired plant lineage is grafted atop a hardy rootstock from another plant. It’s an ancient technique that likely dates back at least 3,000 years. 

Nearly all apples, peaches, pears, plums and similar fruits that we enjoy today are grown using plant grafting.

A grafted Craig’s Crimson cherry at Tyrant Farms (the graft line is clearly visible a few inches above the ground).

Can you graft tomato plants too? Yes! 

In fact, grafting tomatoes is fairly easy to do. You can graft tomatoes to produce extremely vigorous, disease-resistant heirloom tomatoes plants that are also genetically true to the original. This means you’ll get that great heirloom flavor and you’ll be able to save the seeds for future years.

How to graft heirloom tomato plants

There are three basic methods that can be utilized to grow grafted heirloom tomatoes:

1. Approach Grafting
2. Cleft Grafting
3. Tube Grafting

After reviewing the nuts & bolts of all three methods, we decided on Cleft Grafting. Why? It seemed to be the easiest method requiring the least amount of purchased materials. 

Since Cleft Grafting is the only tomato grafting method we have experience with, that’s the method we detail below. (*We did try grafting a couple of tomatoes using Approach Grafting and they all died—this was probably due to our lack of experience, not due to any fault inherent to the method itself.)

Step by step: cleft grafting heirloom tomatoes

Overview:

Cleft Grafting requires slightly larger tomato plants than the other two grafting methods. The tomato plants’ stems should be about 1/4 to 1/2 inch in diameter.

You’ll need one disease resistant hybrid tomato plant and one heirloom tomato plant for each grafted plant you intend to grow. Popular hybrid root stock tomatoes that you grow from seed are:

• Estamino – Has good resistance to fusarium crown and root rot, and intermediate resistance to root knot nematodes, and tomato spotted wilt virus.  
• Fortamino – Has intermediate resistance to tomato spotted wilt virus, root knot nematodes, and corky rot. 

Materials you’ll need for tomato grafting:

• Razor blades (or box cutter),
• Rubbing alcohol in small bowl (to clean the blades before and after cutting each plant),
• Parafilm grafting tape to secure and hold the heirloom plant top to the hybrid root stock base,
• Small planters for each newly grafted plant,
• Spray bottle/mister.

Tomato grafting steps:

1. Start your hybrid seeds before your heirloom seeds. 

Put your hybrid rootstock seeds into small containers about 1 week before you sow your heirloom tomato seeds. The hybrid root stock plants must be at least the same size if not larger than the heirloom stalks you’ll eventually be grafting onto them.

2. Match a hybrid to an heirloom to graft. 

After the plants have produced at least 5 leaves or grown to be 1/4 – 1/2″ thick, pick out a hybrid and an heirloom to graft together. Again, it’s important that the hybrid base be AT LEAST as thick if not thicker than the heirloom tomato’s stem you’ll place on it.

3. Hybrid surgery: make the wedge opening.

At first, it feels really strange to decapitate perfectly healthy tomato plants, but you’ll get used to it! Cut the hybrid plant between 2″ and 4″ above the soil line (do a straight cut parallel to the ground).

Remove any remaining leaves on the hybrid plant base, then cut your “wedge opening.” The wedge opening is a single cut straight down the center of the hybrid stem. You’ll be putting your heirloom stalk in the opening shortly.

4. Heirloom surgery: make the top graft wedge. 

Cut your heirloom plant off of its base parallel to the ground, approximately 2-4″ above ground level. Next, carefully cut a “wedge” on the heirloom’s bottom stem by cutting both sides of the heirloom stem into a V-shape to fit into the hybrid plant base’s “wedge opening.” 

The purpose of this step is to prepare the V-shaped wedge at the bottom of your beheaded heirloom tomato seedling to slip into the wedge opening of the decapitated hybrid tomato seedling.

Next, remove all but the top scion leaves on the heirloom stalk so the plant can put it’s energy into rooting/grafting rather than maintaining its leaves.

5. Join & tape the plants. 

And the two become one! Firmly insert your heirloom wedge (top) into your hybrid wedge opening (base) making sure that at least one side of the outside edge (cambium layer) of the scion is lined up with the outside edge of the rootstock so as to ensure good “blood flow” between the two plants.

Cut a small piece of parafilm off your roll, and stretch it out (not too thick, about 3″ of tape AFTER it’s been stretched so the plant can break out of it when ready). Wrap the strip of stretched parafilm tape around the grafted area.

Some people use grafting clips instead of parafilm tape, but we like tape better since the plant tells you when it’s ready by breaking out of the parafilm tape rather than you guessing when it’s time to remove the clip.

6. Days 1-3: Cover grafted tomatoes and keep them in a warm, humid, dark spot while spraying.

Your freshly grafted tomatoes are going to need a lot of loving. They need to be kept in a humid, dark place completely out of the sun. We put ours under plastic storage bins in our garage during this step.

Keep them very damp for the next three days, using a spray bottle several times per day to spray down the stem and foliage, and keep the roots moist. It’s difficult to overmist during this step. 

7. Days 4-7: Place grafted tomatoes in shade. 

Bring your grafted tomatoes out from the dark, but make sure they’re in a shady spot, watering often until around day 7. If they seem like they’re going strong, try moving them into partial sun but keep an eye on them to make sure they don’t look wilted or stressed.

8. Days 7-10: Bring grafted tomatoes into sun.  

Now it’s time to bring your grafted tomatoes into full sun! Keep a close eye on them, especially when you first move them into sun. If they look limp or stressed, move them back into a shadier spot. Make sure the soil never dries out.  

9. Day 10: Transplant your grafted tomatoes. 

Put your grafted heirlooms into the ground in a full sun spot. Make sure that your graft line is NOT below the surface of the soil, since this will make the heirloom susceptible to whatever diseases are in your soil.