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Determinate vs indeterminate: why does it matter?

When Karen and I planted our 2020 garden, we made the one mistake you never want to make with tomatoes: we didn't check whether the plants we bought were determinant or indeterminate.

Our assumption that the cherry tomato plants would be small (small tomatoes means small plant, right?) and the romas would be big, was 180 degrees wrong.

The Great Green Goddess of Gardening was on our side, however. Karen has been able to stake up the indeterminate cherry tomatoes -- and the determinate romas have plenty of string fencing to grow on.

I've been asked to write more about the differences between indeterminate and determinant tomato plants. Since I clearly needed to review, I'm glad to do so.

In simple terms, determinate plants are like bushes or shrubs; indeterminate plants are like trees. Determinate plants are genetically set to grow to a certain size and stop. Indeterminate plants will keep producing stems, leaves and fruit as long as they get enough water, light and warmth.

Indeterminate tomato plants

During the first month of an indeterminate tomato plant's life, it can grow so fast that it doubles in size about every two weeks. 

If it isn't supported, the weight of the fruit and the side branches will cause the plant to fall over on to the ground. When the main stem is horizontal, the plant has an even greater tendency to branch out to the sides. 

A healthy indeterminate tomato plant that isn't supported can easily cover a four-foot by four-foot area with as many as 10 stems, each three to five feet long. At this point, you'll have a bramble. The leaves will shade themselves. The fruit will fall to the ground and rot. Bugs and disease will be attacking the plant.

It can be a challenge to keep up with a fast-growing indeterminate tomato plant, even if you do stake it up.

Staking and pruning are critical to having a healthy indeterminate tomato plant. Side stems or branches should be pruned away below the first flower or fruit cluster. Then as the plant grows, you should prune away suckers, the branches that start in the crotches or axils between the leaves and the main stem. The suckers appear from the bottom of the plant upward, which is why you need to be pruning early.

With fewer stems and side branches to feed, more of the plant's resources can go into producing larger fruit steadily throughout the growing season. With fewer, well distributed branches, the leaves are exposed to the sun.

Supporting the vine is important for its health and productivity -- and for ease of harvesting. Forget about the standard tomato cages that can be found in garden centers. 

An indeterminate tomato vine needs sturdy stakes at least five to six feet high; the plants can grow up to 10 feet tall and get heavy.  Having fencing or a trellis along the stakes early in the season can also be helpful to stretch branches out sideways. You'll find a variety of ideas for tomato supports here. There's plenty of room for creativity.

Many popular tomatoes such as Beefsteak, Big Boy, Brandywine, Sungold and Sweet Million, are indeterminate. As Karen and I discovered, cherry tomatoes can be indeterminate.  Most heirloom tomatoes are also indeterminate. 

The advantage of indeterminate tomatoes is a season-long producer of fresh tomatoes. Indeterminate tomatoes tend to be big enough to cover a sandwich or eat like an apple.

Determinate tomato plants

These plants grow in a defined pattern: they stop producing shoots once flowers form on the ends. This is followed by a burst of ripening fruit and a final leaf expansion. The fruits develop and ripen in a short time frame, about two weeks. As the fruit ripens, the leaves age and drop off.

Commercial growers like this type of tomato because plants can be mechanically harvested at the same time. For home growers, the advantage is an early harvest. This is good if you want a lot of tomatoes at one time for canning or canning tomato sauce. These are also a good choice if you have a short growing season.

Most determinate plants grow to four to five feet tall. Some versions of these can be grown in containers such as Patio Princess, Bushsteak, Tumbler, Patio F1 Hybrid, Bush Early Girl, Baxter's Bush Cherry, Sweet Baby Girl, Tumbling Tom Yellow or Balcony.

They, too, should be supported because the ripening fruit are heavy. Cages are often too small, but galvanized fencing with openings at least four-inches square can work.  It can be curled into a cylinder and wired together at the edges to make a large cage. It should be stabilized with two stakes. You can wire the cage to the stakes. You can also stretch fencing out horizontally and support it with stakes.

Examples of determinate tomatoes are Romas, San Marzano, Amish Paste, Celebrity, Marglobe and Rutgers.




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