Grafting Tomatoes – By Master Gardener Dennis Adamson
By Alan on Jun 05 in Blog tagged bleach solution, cotyledons, Dennis Adamson, Dr. Larry A. Ruff, grafting, grafting clips, grafting tomatoes, healing chamber, Lehi, Master Gardener, moisture probe, razor blades, rootstock plant, scion, seeds, sterile water, temperature, Thanksgiving Point Gardens, transplant, Utah | Comments Off
Week 60: Grafting Tomatoes
I am going to delay the overall propagation article until the next week. In last week’s article I talked about Dr. Larry A. Ruff’s description of grafting heirloom tomatoes onto more vigorous, disease-resistant tomato rootstalk. This was part of one of our Advanced Master Gardener lectures at Thanksgiving Point Gardens Lehi, UT.
I looked on the Internet for the grafting clips and found a seller that had 15 for $10. I checked with one of the seed companies and found that for an additional 50% cost I could get 200. I have already received them and included was 6-page information sheet on the correct tomato grafting procedure. I thought that those who want to try this would enjoy a full description of the process.
They recommend starting the seeds for grafted tomatoes 6-8 weeks before transplant. If one is faster growing than the other then start the slower growing ones a day or two before the faster growing ones so that the stalks will be nearly the same diameter at grafting. (Later, in the article, will be a description of a way to get around this.) Also, grafted tomatoes stop growing during the healing process so they will take one to two weeks longer to get to the transplant stage. They also recommended over-seeding by 25% so that you will have plenty of plants to attempt the grafting.
The plants are usually ready to graft 2 ½ to 3 weeks after sowing. The easiest way check, if they are ready to graft, is to take a 2mm grafting clip and make sure the stalk fits snuggly into it.
They recommend the soil temperature be 80°F (27°C). This can be obtained by using with a soil heating mat and a soil temperature probe. After germination reduce the temperature to 64-66°F (18-19°C) to encourage a stockier plant. They will also need sunlight or grow lights at this point.
Be as sterile as possible in the grafting process. They recommend washing the work area with a bleach solution. Thoroughly clean your hands or use surgical type gloves and don’t smoke in the grafting area. It is best to do it indoors where there is a constant temperature, out of the sunlight and with no fan or draft present. Always use new razor blades and clips. 
The grafting procedure starts by taking the rootstock and cutting the stem with the razor blade at a 45° angle just below the cotyledons. The cotyledons are the embryonic first leaves of the plant and usually have a different appearance than the later leaves. They will be the bottom leaves when the plant forms other leaves. The scion is the portion of the plant that contains the desired leaves, flowers or fruiting portion that carries the genetic portion of the plant that you wish to duplicate. Find a scion whose stem matches the diameter of the rootstock stem and sever it, again just below the cotyledons at a 45° angle. If the stalk is too large on the scion at this point, then move above the cotyledon to where the stem matches the diameter. The same technique can be used if the rootstalk is too large in diameter. If this is done then the rootstock may re-sprout from latent buds. These can be removed later. Some people will remove all but the leaf at the growing point to decrease respiration and the number of leave for the plant to support. Experiment to see which works best in your hands. Put the grafting clip ½ way over the rootstalk half and then put the scion half in place, matching up the angled ends. If the temperature is hotter than desired, mist the plants before grafting. You can continue to re-mist in the healing chamber or go high tech and use a cool mist humidifier in the chamber. Another tip is to put the scions in sterile water to keep them moist if you want to do more than one at a time. If you do multiple sessions of grafting, change the razor blade and re-sterilize the area and your hands.
They recommend a ‘healing chamber’, near the grafting station, to minimize the movement of the grafted plants. 
The healing chamber keeps the plants at high humidity (80-95%) and in indirect low light to diminish their respiration and drying while the new vascular components reconnect at the graft site. The soil should be kept at 71-74°F (22-23°C). Water the plants the day before planting, but not on the day of grafting. Too much water in the soil will send water up the stalk and push the scion off the graft junction. Try to keep the chamber closed for 3 days while monitoring them from the outside. If they appear to be wilting, you should raise the humidity level. On the 4th day open the chamber and check the moisture level, preferably using a soil moisture probe. 
If you need to, water the plants using a bottom watering method and then reclose the chamber. On the 5th day allow the humidity to slowly decrease by opening the chamber a small amount. If wilting occurs, close again and retry each subsequent day. Eventually you will get the plants to where they are thriving without the cover on. The plan is to gradually getting them to normal greenhouse temperature and humidity. After a few days in the greenhouse or similar conditions they are ready to be handled. The silicone clips should fall off by themselves as the stem increases in diameter. They claim that the spring-loaded clips have a greater potential to constrict the growth of the stem.
When you plant the grafted tomatoes, be sure that the graft site is about the soil level or the scion will send out roots and negate the whole grafting process. Also prune any suckers as they develop since these will grow into a rootstock plant. At this point treat a grafted tomato the just as you would a normal tomato.
The following site is the source of most of the information in their article and also has step-by-step photos of the process.
https://www.johnnyseeds.com/t-growers_library.aspx
This will give you their grower’s library and you can click on: Grafting Tomatoes for Increased Vigor and Disease Resistance.
Another positive factor with grafting is that the yield appears to increase. In 2010 Johnny’s research farm in Albion, Maine used 3 plants from 5 different tomato varieties and grafted them onto a hardy rootstock. They also grew 3 plants on their own rootstock. They showed an average of over 40% greater yield on the grafted plants with one, Geronimo being 66%. The full data can be found by going to the above site and then to: Grafted Tomato Yield Data.
Another site that has step-by-step photos and instructions is:
http://therealgarden.com/2011/04/tomato-grafting-time-to-cut/
Alma 16: 17 … “but that they might receive the word with joy, and as a branch be grafted into the true vine, that they might enter into the rest of the Lord their God.”
