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Grafting Could Give Tomato Plants Higher Yield, Tastier Fruit

Jul 13, 2016

Farmers markets are full of bright colored produce at this time of year. Think sweet stone fruit, tart berries and tomatoes of every color. People love tasty heirloom tomatoes but they can be hard to grow and they’re expensive. That’s why researchers want to create a stronger plant. They’re doing this using a new twist on an old technique.

Scott Stoddard is an expert when it comes to tomatoes. He plants rows and rows of the fresh-market crop on farms across Merced and Madera counties for the UC Cooperative Extension. 

Scott Stoddard hopes these little seedlings when full grown yield a large amount of tomatoes.
Credit Ezra David Romero / Valley Public Radio

“They end up on sandwiches at Subway,” Stoddard says. “Also at any of your common hamburger places, In-N-Out, McDonald's, you name it.”

Right now those tomatoes taste fine and yield plenty, but he wishes they were more flavorful and had an even larger crop. So today he’s conducting something of an experiment at a farm north of Madera.

He and a crew of farmworkers are planting 3,500 seedlings about a foot and a half from each other using this machine called a finger planter.

“So it grabs the planter and it swings around towards the bottom and opens it up at the bottom and drops it in there and there is also water going into here,” says Stoddard.

But unlike the rest of the tomato plants grown in this field - or almost any outdoor field in California - these tiny shoots are grafted.

Stoddard’s taken disease-and-insect-resistant plants, cut the top off them and placed the tip of a weaker but tastier yielding tomato plant into the exposed tissue. The plants live in a greenhouse for a couple months where they slowly fuse together before they’re ready for planting.

Scott Stoddard hopes that each of these little tomato plants will yield enough to make up the cost difference of grafting.
Credit Ezra David Romero / Valley Public Radio

“Now we got them in the field and so approximately 83 days from now, if all goes according to plan, we will be harvesting out here and we will see if we can see some yield differences,” Stoddard says.

Grafting is used for all sorts of trees, but is used less for plants like tomatoes for large-scale outdoor production. The process is a workaround for temperamental soil and pests like little worms called nematodes. 

"The hypothesis here is that rootstocks will provide an economic yield increase of these varieties over an un-grafted plant." - Scott Stoddard

The growing technique has proven successful for tomatoes grown in hot houses, but Stoddard wants to see how the grafted plants will do out in the open planted in Central California’s nutrient rich soil.

“The hypothesis here is that rootstocks will provide an economic yield increase of these varieties over an un-grafted plant,” says Stoddard. “That’s what we’re testing to see if that’s true.”

He’s fairly certain the crop will take off, but he needs to make sure grafting will pan out economically before he recommends the practice to the growers he advises. He says since grafted plants are more expensive than regular seedlings he will need to see at least a 30 percent increase in yield.

“They are very price sensitive,” Stoddard says. “This is why it’s experimental. So we do this on a very small basis and see if there’s something potentially there that the growers might end up taking and moving on with.”

Grafted tomato plant.
Credit Ezra David Romero / Valley Public Radio

About 150 miles north of this farm in Madera, Margaret Lloyd a UC Cooperative Extension farm advisor for Yolo, Solano and Sacramento counties is also grafting tomato plants. But she’s grafting heirloom varieties onto soil resistant plants at UC Davis.

Lloyd says heirloom tomatoes have a harder time fighting off disease and can easily bruise or break open.

Once the plants are grafted they are kept in a nursery until they are ready to be planted.
Credit Ezra David Romero / Valley Public Radio.

“We’re kind of working at this level of finding non-chemical management tools that will help overcome these challenges so they [farmers] can continue to grow these nice heirloom varieties,” says Lloyd.

She’s planted a quarter-acre field of the most common heirloom types – Brandywine, Cherokee purple and Marvel Stripe – as well the yellow Sun Gold Cherry tomato and a salad variety called Charger.

“We’re trying to understand some of the initial questions about whether these heirloom varieties that we're interested in can be grafted and how these combinations might perform under our environmental conditions,” says Lloyd.

Just like Stoddard, Lloyd is collecting data from the trial to see if grafting makes sense for the growers she represents. If both projects are successful Lloyd and Stoddard agree that consumers could, in time, have a tastier larger assortment of tomatoes for purchase in stores and at farmers markets.