- Cut the plant's root system. The experts at Washington State University Extension say: “A stressed plant will hurry to produce offspring before it dies. One way to stress a plant is to cut it's root system. Push a shovel into the soil halfway around the plant, about 8 to 12 inches from the base.”
Hi. I've done the root-pruning method and it worked very well for me. I'd never heard of it until I read Dick Raymond's book, Joy of Gardening. If I recall correctly, this is what he suggested, and what I did:
1) Wait until the tomato plants have set fruit and the fruit are a good healthy size, that "they've been big and green for a week but they're still not getting ripe!!" look.
2) Take an ordinary garden shovel or spade, and using the width of the shovel/spade blade -- usually about eight inches at the digging end -- measure off about eight inches from the stem at soil level.
3) Eight inches away from where the plant stem goes into the soil, push the shovel/spade straight down into the soil on three sides of the plant. Not four; three. (The goal is to prune the roots back around most of the plant, not to kill it.)
4) Water the tomato plant right away after you prune it. Might be a good idea to do the root-pruning and watering in the early evening, so the plant has time overnight to recover.
Raymond said the damage to the plant would cause it to immediately start to ripen fruit, and I found it worked. Within a day or two, green tomatoes started turning red. My plants kept producing new flowers and fruit after the pruning, and they stayed productive into the first hard frost.
The main caution I would advise is to wait until the green tomatoes are looking full-sized for the plant. I've never tried root-pruning with immature fruit; just plants which had full-size fruit that were in that long, slow, waiting-to-ripen stage.
FWIW, I did this in a backyard garden in Toronto where the owner and another tenant also had gardens, and both prided themselves on the quality and size of their tomato plants. Felt kinda good to have the first ripe ones of the season.
The hashplant had 8 weeks, I harvested her mid nov but her buds are small.