Growing Things: The finer points on pruning tomatoes

Q

I was wondering if you could discuss the practice of pruning indeterminate tomatoes. I’ve been pruning mine with varied success. I find the yields, particularly on the heirloom varieties, can be quite small. I once grew a grafted purple Cherokee tomato and did not prune and I had great yields, but I have not been able to replicate that success. I don’t know if my mom just grew determinate types, but I don’t recall her ever pruning her tomatoes. Have gardeners always pruned their tomatoes? Is it absolutely necessary? Are there different advantages on pruning/not pruning in shorter growing seasons like mine?

A

This is one of those gardening questions that has as many answers as there are gardening expert opinions. I did a quick search on the current state of how the gardening community feels about pruning indeterminate tomatoes and stopped after the first two articles because both were diametrically opposed viewpoints.

​Let’s begin by defining what an indeterminate tomato is. According to Wikipedia, “Indeterminate tomato plants are perennials in their native habitat but are cultivated as annuals. Determinate, or bush, plants are annuals that stop growing at a certain height and produce a crop all at once.” In other words, indeterminate tomatoes just keep on growing throughout the season while determinate grow, stop and produce all at once.

​Since an indeterminate tomato will have blossoms and fruit throughout its entire life pruning is the best way to contain the plant since these tomatoes grow unchecked. Researchers at Purdue University found that pruning, namely, removing branches below the first main stem, increased the average fruit weight in some cases but not the total yield for each plant.

​Many indeterminate types will produce as many as 10 or more stems. My advice for pruning indeterminate types is to prune them back to two main stems. I do this pruning early in the growing season to keep the plants contained and to keep them from taking over the tomato patch. This pruning method will usually produce larger but fewer fruits. If you want more fruit, try pruning to four main stems. I also search the plant during the growing season for ‘suckers’ that are not going to develop into a stem. These suckers appear in the crotch between the stem and a branch. I pinch these out with my fingers.

I don’t remove all of the suckers leaving two or three to improve the yield. I used to cage my indeterminate types but I now stake them. When caged they required less pruning perhaps to four or five stems and now two stems with the staking.

​As for your question on whether there’s an advantage or disadvantage to pruning in short-season areas like ours — my opinion is that there’s no advantage to not pruning. I have always had good success growing indeterminate tomatoes by pruning, and this is supported by an excellent paper from the University of Idaho on growing tomatoes in shorter-season locations.

​Revitalizing foliage

Q

I have some blue oat grass in several locations in my garden. My question is, should I be cutting the grass down in the spring so it can grow new?

A

Yes, you should remove the old foliage before the new leaves emerge neat in order to keep the plant looking and tidy. Every two to three years, divide the clump in the early spring. The division seems to renew the plant vigour and keep it energized. I’ve seen many of these grasses look old and tired without being divided.

Learn more by emailing your questions to [email protected], reading past columns or my book Just Ask Jerry . You can also follow me on Twitter

@justaskjerry01.

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