Growing Grapes in Your Backyard
|Topic||What is trunk girdling and how do I do it?|
Trunk girdling is the removal of a thin strip of bark all the way around the trunk. It is done each year on an area of the trunk or cordons that was not girdled in previous years. The practice temporarily disrupts the downward flow of carbohydrates and hormones through the phloem (inner bark) and, when timed properly, increases the berry size of most seedless table grape varieties. It can make berries about 10 to 30 percent larger when done correctly. For best results, it should be done about 10 days after full bloom – generally in mid to late May. Trunk girdling should only be done on mature vines that are at least 4 to 5 years old. If the trunk is thick and convoluted, consider girdling main branches, and consider girdling only some branches so you can see for yourself the difference in berry size from the girdling compared to branches not girdled.
Girdling knives can be purchased at vineyard supply stores and through the internet. They have two blades that are a specified distance apart. You could also use two single cuts, but it can be difficult to make a uniform strip width.
Begin by removing the loose bark in the area to be girdled. The width of the strip should be about 3/16 to 1/4 in. wide. It is essential that all of the phloem tissue is removed, so press fairly hard. Check for completeness about 20 minutes after the girdle is made – a proper girdle will have the appearance of an all-white, fibrous ring of wood (xylem). Remove any brown portions of the ring; if there is even 1/8 in. of phloem tissue left, the girdle's benefits are lost. Be sure not to cut so deep as to damage the water-conducting xylem and weaken the vine. With a proper cut, the ring should pull out easily. Callus tissue will begin to grow from where the cuts were made and callus growth will progress inward. Within several weeks the bark will reform.
Photos (pdf): Before and after photos of pruning overgrown vines on an arbor. Photos: Chuck Ingels