Some of you may have seen grafted tomatoes cropping up in garden centers over the past couple of seasons. But what really is the difference between a grafted tomatoes and non-grafted tomatoes? Grafted tomatoes have turned up for many of the same reasons that we graft other plants. Tomato grafting first because practice in the 1960s when grafting was mainly done to make the tomato plants more disease resistant. Now, grafting is done for a number of different reasons. Sometimes growers graft tomatoes so that they are more resistant to abiotic stresses (salinity, drought, flooding) or they choose rootstocks that are better suited to their growing conditions (soil, temperatures, etc). This hardier rootstock is then attached to a scion (aka "the top part") of a variety that the growers want. In some cases, grafting can also cause the tomato plant to be higher yielding, extending it's growing season at the beginning and the end.
One common factor among grafted tomatoes that you'll see when you're shopping around your garden center this spring is that, usually, these plants are more expensive than your normal tomato plants. For some, the cost is worth it for the higher yield and higher tolerance to several factors. But if you want to try your hand at grafting and skipping the higher prices at the register, here's a step-by-step tutorial for grafting your own tomato plants.
Step 1: Choose your rootstock. This really dependent on your zone and what you want your rootstock to do for your plant. Johnny's seeds has a whole section devoted to tomato rootstocks that you can find here. Clicking through them you can see what they're best for (resistances, vigor, etc) and find what you need.
|We used Early Girl as our rootstock.|
Step 2: Pot up your rootstock like you would any tomato. The one difference is you want to leave a good amount of the stem above the soil line. Usually it's good practice to sink some of the stem below the soil to initiate more root growth. In this case, you need a good amount to work with so keep a lot above ground. If you have time, you can even leave this tomato to grow a few days in it's new pot to ensure that the roots are healthy and strong before you graft.
|One of the Early Girls awaiting decapitation.|
Step 3: Decapitate your rootstock. That's right, chop it right off. Using a razor blade is generally the best way to do this. Our department has a lot of them sitting around for this purpose. You want to behead the plant below the cotyledons because if you cut above them, they will eventually turn into suckers on your mature plant, cutting down on yield.
|Our cuts were just below the cotyledon leaves.|
|Our sad-looking decapitated Early Girl.|
Step 4: The next few parts take a bit more precision and skill than the earlier parts. We grafted our tomatoes a bit earlier than normal so our plants were TINY. You can probably do this much easier with a little bit larger tomato plant. You'll need to make a cut directly down the center of the remaining rootstock to make the slot where the scion will sit. This cut can be a few centimeters long. We made our cuts so that they were as deep as our razor blades (shown in the picture above).
|A little bit fuzzy, but you can see the cut.|
Step 5: Choose your scion. This is the top part of the plant that you will get all the growth and, most importantly, the fruit from. You can really choose any variety that you like best for this.
|We used Striped Marvel tomatoes for our scions.|
Step 6: More decapitation! Cut off the top of your scion, leaving a good amount of stem to work with. This way, if you make a mistake, you can cut it off and still have more stem left.
Step 7: Shave off the outer parts of both sides of the stem so you have a wedge. The wedge should be about as long as your cut into to rootstock that you make in Step 4. This way it will fit into the cut on the rootstock nice and snug with not much wiggle room.
|If I were to turn this over, the other side of the stem would look the same.|
Step 8: Fit the pieces together. This might take some delicate maneuvering, but your scion wedge should fit into the cut rootstock pretty well.
|The scion and rootstock wedged together.|
Step 9: Wrap the graft area with parafilm. This stretchy material is probably the best way to keep a graft together and help it heal well. This might be tricky keeping the scion and rootstock in the right position while you wrap the stems, so you might want to enlist a second pair of hands to hold them in place for you while you wrap it up.
Step 10: Keep your grafted plant well cared for. Mist your plant regularly so it doesn't dry out and the plant can take in moisture through the leaves while the graft is still healing. Place it in an environment with less light and moderate heat. Do not place it in bright, direct sunlight or a hot environment. This will stress the plant and cause the graft to fail. Grafts usually take about a week to successfully heal.
There you go! And this information is coming from one of our graduate students who studied grafted tomatoes for a research project, so I'm hoping that's pretty reliable. His one word of caution is that you will find many resources that teach tube grafting, where you forgo any wedge cutting and just stick the top on the bottom and wrap it up. One of the big reasons that this method I described above (called cleft grafting) is more successful is because there's more tissue area touching and able to bind together. Pretty simple, but be careful with tutorials that teach you tube grafting. You might not have as much success.
For more info on grafting check out this Organic Gardening article or, if you want to get super science-y, you can find the research from our graduate student teacher here.