What Are Grafted Tomato Plants? (Plus 5 Rootstocks)


Grafting tomato plants seems like a strange idea at first.  However, grafting can give you a big advantage in growing healthy plants and getting a better harvest.

So, what are grafted tomato plants?  A grafted tomato plant comes from two tomato plants of different varieties combined into one.  The bottom plant (rootstock) provides the roots of the new plant, and the top plant (scion) provides the stem, branches, leaves, flowers, and fruit of the new plant.  Grafting involves cutting both plants, attaching them at the cuts, and waiting for the two to heal together, forming a graft union.

Of course, there are lots of different options for both the rootstock (bottom part) and scion (top part) when grafting tomato plants.

In this article, we’ll talk about methods for grafting tomato plants, along with benefits and drawbacks of grafting.  We’ll also take a look at some equipment you need for grafting tomato plants.

Let’s get started.

What Are Grafted Tomato Plants?

A grafted tomato plant comes from two tomato plants of different varieties combined into a single new plant.  The two parts of a grafted tomato plant are:

  • Rootstock – this is the “bottom” part of the grafted plant.  The rootstock provides the roots of the new plant.  Ideally, the rootstock provides a strong root system with resistance to soil borne diseases.
  • Scion – this is the “top” part of the grafted plant.  The scion provides the branches, leaves, flowers, and fruit of the new plant.  Ideally, the scion provides good quality fruit that produces a good yield.
tomato plant roots
Find a rootstock with strong roots and good disease resistance.

In order to graft, both plants are cut above the cotyledons.  The cotyledon is the set of leaves that appear at germination – they are not “true” leaves.

After the rootstock and scion are cut, the bottom of the rootstock plant and the top of the scion plant are attached where they were cut (this point of attachment is called the graft union).

grafted tomato plant
The graft union is where the rootstock and scion were joined and healed together.
Image courtesy of: Carrivard via Wikimedia Commons https://commons.wikimedia.org/wiki/File:Tomato_graft_union.jpg

Once the wounds at the graft union heal together, the two plants become a new one.  The new plant has the best characteristics of both plants: strong roots, good disease resistance, excellent fruit quality, and interesting colors (such as tomatoes with purple skin or flesh).

There are many rootstock tomato plants to choose from (I have included 5 of them in a list later in this article).  You can graft heirloom or hybrid tomato scions onto these rootstocks.

Tomato Grafting Methods

There are a few different methods you can use when grafting tomato plants:

  • Approach Grafting – this technique is also known as Side Grafting or Side By Side Grafting.  It has a higher success rate, and can be used for larger plants.  However, it is more difficult and slower than the other methods.
  • Cleft Grafting – this technique is also known as Wedge Grafting.  The graft union is more secure than with tube grafting, so the rootstock and scion are more likely to hold together.  However, it takes more time than tube grafting.
  • Tube Grafting – this technique is also known as Splice Grafting or Japanese Top Grafting.  It is probably the easiest method to learn.  However, it requires grafting clips to hold the rootstock and scion in place so the graft union can heal.

You can see illustrations of these three grafting methods on the University of California website.

Tube grafting is probably the most common method used.  In this technique, both the rootstock and scion are cut at matching angles (usually 45 degrees for both).

tube grafting tomatoes
Both the rootstock and scion must be cut so that they can heal together into one new plant.
Image Courtesy of User Caryrivard via Wikimedia Commons: https://commons.wikimedia.org/wiki/File:Tube_Grafting_Technique.jpg

A grafting clip attaches them together at the graft union, allowing them to heal into one plant.  According to the Purdue University Extension, tomato stems should be at least 1.5 millimeters before grafting.

There are various sizes of grafting clips available, but the smallest are usually 1.5 millimeters.  The largest grafting clips are 3.0 millimeters.

When tomato plants are larger than this, it becomes difficult to provide the conditions they need to recover from the grafting process.

Generally, tomato plants will be ready for grafting 2 to 3 weeks after planting seeds.  However, you can use a grafting clip to check the stem size to be sure.

If the stem fits snugly inside the grafting clip size you have chosen, the plant is ready for grafting.  Just make sure that both the rootstock and scion are ready at around the same time!

According to the Colorado State University Extension, the healing process for grafting tomato plants takes around 2 weeks.  So, take this delay into account when planning your garden.

When grafting tomato plants, do not allow the cut ends to dry out.  The University of Massachusetts suggests that the cut surfaces will dry out in just a few minutes.

Instead, cut one rootstock and one scion at a time.  After you graft them together, move on to cutting the next set.

tomato seedling
Cut and join one pair of tomato rootstock and scion at a time. Cut ends of plants dry out fast.

After successful grafting, Johnny’s Selected Seeds suggests that you transplant the new tomato plant outdoors with the graft union above ground.

This prevents the scion (the less disease resistant variety) from coming into contact with the soil.  This protects it from any diseases that may be present.

Are Grafted Tomato Plants Better?

In many ways, grafted tomato plants are superior to their non-grafted cousins.  There are some drawbacks to grafting tomatoes, but they are outweighed by the benefits.

Benefits Of Grafting Tomatoes

There are several advantages of grafted tomato plants, including:

  • Strong Roots – when grafting, you can use rootstock from plants with larger, more extensive root systems.  This gives the grafted plant good drought tolerance and the ability to provide more water and nutrients for the fruit on the scion.  A strong root system also increases a grafted plant’s tolerance to environmental conditions like heat, cold, and salinity (saltiness).
  • Excellent Fruit – when grafting, you can choose a scion that produces fruit with good flavor and quality (such as many heirloom varieties), without the need to worry about disease resistance.
  • Disease Resistance – grafting allows you to select a rootstock that resists common soil borne diseases, including: Early Blight, Late Blight, Fusarium Wilt, Verticillium Wilt, and Bacterial Wilt. You can find a list of blight resistant tomato varieties here.
  • Increased Yield – when combined with a strong rootstock, a scion can provide more fruit, since the roots can deliver more resources than is possible with the scion’s natural roots.
dying tomato plant
Grafted tomato plants have better resistance to diseases such as Bacterial Wilt.

Although these are strong incentives to try tomato grafting, it is true that grafted tomato plants also have some drawbacks.

Disadvantages Of Grafting Tomatoes

Two of the biggest drawbacks of grafted tomato plants are:

  • Increased Cost – if you purchase grafted tomato plants, expect to pay more.  There are extra costs all around: for example, the labor to raise twice as many plants, cut them, and graft them, not to mention the extra time to let the graft heal.  If you do this work yourself, you will still need to buy equipment and twice as many seeds.
  • Lost Seedlings – the grafting process is not without risk.  The wound could become infected, or the plant could die.  This means you will need to plant more seeds, increasing costs further if you graft your own tomato plants.
tomato seedling
If you want grafted tomato plants, you will need to raise at least twice as many seedlings.

Tomato Grafting Supplies & Tools

If you do decide to graft your own tomato plants, there are some tools and supplies you will need to get started, including:

  • Grafting Clips
  • Grafting Support Stakes
  • Grafting Knife
  • Grafting Healing Chamber

We’ll start with grafting clips, which are necessary for the tube grafting method that we discussed earlier.

Grafting Clips

Grafting clips are placed over the graft union between the rootstock and scion.  A grafting clip holds both plants in place so that the cut ends can heal together to form a single new plant.

Johnny’s Selected Seeds has top grafting (tube grafting) clips in various sizes, from 1.5 millimeters to 3.0 millimeters.

Johnny’s also has side grafting clips available if you prefer the approach grafting method.  These clips are spring loaded and available in different sizes that will hold both younger plants (1.5 millimeters) and larger plants (up to 6.35 millimeters).

Grafting Support Stakes

Grafting support stakes work with top grafting clips to provide support to grafted tomato plants as they heal together.  These support stakes from Johnny’s Selected Seeds are 6 inches long and made of polypropylene.

They have pointed ends, so they go into soil easily.  These stakes only work with top grafting clips that have a channel for the stakes.

Grafting Knife

A grafting knife is used to make cutting tomato plants faster, easier, and cleaner.  This miter-cut grafting knife from Johnny’s Selected Seeds makes cuts at the proper angle, and is spring loaded so it opens automatically after cutting.

When cutting plants for grafting, be sure to keep the environment sterile.  Wash your hands, and use alcohol to clean the grafting knife between cuts.

Grafting Healing Chamber

A grafting healing chamber provides grafted tomato plants with the conditions they need to heal at the graft union.

The proper conditions for a grafting healing chamber include:

  • Warm Temperature – the ideal temperature is 72 to 85 degrees Fahrenheit (22 to 29 degrees Celsius).
  • High Humidity – the ideal humidity level is 90% or more.
  • Low Light – this reduces stress on plants as the graft union heals.

The Colorado State University Extension suggests that you use a Styrofoam box as a grafting healing chamber.  Put a tray of water at the bottom to maintain humidity levels.

Styrofoam prevents water from leaving the chamber, which keeps humidity levels high.  It also acts as insulation to keep the inside of the chamber warm.

For the first few days, cover the chamber with a blanket to ensure darkness inside.  After that, remove the blanket and gradually increase the humidity and expose the grafted plant to light.

Open the chamber twice daily to replace water and air inside.

If you like, you can also buy grafting starter kits from Johnny’s Selected Seeds:

5 Tomato Rootstocks To Use For Grafting

The ideal rootstock will have a large, strong root system and resistance to common tomato diseases, such as Bacterial Wilt, Fusarium Wilt, and Verticillium Wilt.

Here are 5 varieties of rootstock tomato seeds to use for grafting:

The ideal soil temperature for tomato seed germination is 65 to 85 degrees Fahrenheit (18 to 29 degrees Celsius).  At this temperature, expect seeds to sprout in moist soil in 6 to 11 days.

For more information, check out this article on grafting from the Purdue University Extension.

Can You Save Seeds From Grafted Tomatoes?

You can save seeds from grafted tomatoes.  Remember that the seeds will come from the fruit, which comes from the scion (not the rootstock).

tomato seeds
You can save seed from grafted tomatoes, but they will come from the fruit (scion), not the rootstock.

Also, remember that plants grown from hybrid tomato seeds may not resemble the parent plant.

Can You Graft A Tomato Plant Into A Potato Plant?

You can graft a tomato plant into a potato plant.  Tomatoes and potatoes are in the same family (nightshade).

The result of grafting a tomato plant onto a potato plant is often called a pomato.  It produces tomato fruit on top (from the tomato scion) and potato tubers in the soil (from the potato rootstock).

You can learn more about grafted pomato plants in this article from Wikipedia.

Conclusion

Now you know what grafted tomato plants are, how to graft plants together, and what equipment to use.  You also know about the benefits and drawbacks of this method.

If you are concerned about disease affecting your tomato plants, crop rotation can help – you can learn more about how to do it here.

You might also be interested in learning about what you can use for tomato ties.

I hope you found this article helpful.  If so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!

~Jonathon

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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