Wednesday, May 3, 2017

Determining tomato varieites

The pun in the title is meant to call attention to the growth habit of tomatoes as gardeners pick varieties for planting this month.

Determinate tomato growth ends in a flower while indeterminate types produce vegetative growth and flowers until frost. Of course there are some inbetweens. They are  known as semideterminate types but even that doesn't fully capture growth habits as some are sprawling and some short, upright plants.

Determinate 'Fantastico' F1 hybrid
grape tomato. All-America Selections.

What's the big deal about growth habit other than considering it in allocating garden space, planting distances and staking needs? A lot.

Last time I wrote about the narrow temperature range for pollination of flowers. Determinate types tend to produce flowers all at once and then not many additional ones as they top out. That is great if you want many tomatoes at one time for canning or marketing. It doesn't work out so well if the bulk of flower production occurs during a cold or hot period that is poor for pollination and results in few fruit.

The other consideration is fruit flavor. As Randy Gardner, tomato breeder at the Mountain Horticultural Crops Research station of North Carolina State University, has been noted as saying, the fruit of determinate types will never have the flavor of indeterminate types. They don't produce the ample amount of leaves to photosynthesize and supply fruit that indeterminate types do. He is the breeder of the "mountain" tomato series including 'Mountain Spring' and 'Mountain Merit'. Both are 70-some day to maturity types and are recommended for commercial growers in Colorado.

Mr. Gardner has also said in interviews that his varieties are bred for commercial producers but were adopted by home gardeners in the East when an outbreak of late blight widely took out plants a few years ago. We have little problem with late blight in the dry West, especially if you water at the soil level and keep foliage dry (no overhead sprinklers).

While Mr. Gardner and other plant breeders have bred more disease resistance into their hybrids than heirlooms have, that generally isn't a big reason for choosing varieties here unless you have a problem with TSWV or some other specific disease.

In general I recommend that home gardeners choose indeterminate types or at least a mix of indeterminate and determinate. Even if you want to grow tomatoes for paste you have the choice of indeterminate 'San Marzano' or newer, shorter-season indeterminate hybrids rather than determinate 'Roma'.

Know the growth habit of the variety you are planting as well as the days to maturity (80 days or less in Denver) before purchase.

Photo Credit: 'Fantastico' F1 tomato - All-America Selections