I am sure you have heard of determinate tomatoes and beans. I have known about them for years and knew they formed bushes and produced all of their fruit at one time. After that, they stop growing.
Turns out that most of the things I thought I knew about determinate plants is wrong! Not only that, but 99.9% of the gardening information about determinate plants online, in books, in seed catalogs and even Master Gardening Groups is incorrect.
Why should you care? This myth can cause you to grow the wrong type of vegetable.
The Gardener’s Definition of Determinate Plants
Gardeners have been taught that determinate plants, such as tomatoes, peas and beans, have the following characteristics.
- They have a bush form and a fixed mature height.
- They produce all of their fruit at one time.
- The plant stops growing once the fruit is ripe – the season for them is done.
- The fruit is usually ripe sooner than indeterminate varieties.
If you do a Google search you will see that all of the common sites use some form of this definition. I have known and taught these characteristics for 30+ years.
It is wrong!
It is true that determinate varieties tend to be smaller and grow in a kind of bush form. It is really just a short vine, but I don’t have a problem calling it a bush form.
Many determinate varies do set fruit sooner than indeterminate varies, so that point is also valid.
It All Starts With Observation
My journey of discovery started bout 4 years ago. I had always grown indeterminate beans and tomatoes because I wanted a long harvest season. I want fresh produce to eat and I was not interested in canning a big one time crop.
The problem with this approach is that both beans and tomatoes are warm crops that can’t be planted until well into spring. So my harvest did not start till about the first of August. So one year I planted some bush beans, hoping to get an earlier harvest, and it worked. They were ready for harvest several weeks before the pole beans.
After the first harvest I noticed something funny. The bushes kept growing and produced more flowers. In fact they produced beans constantly right up until frost. I had the same result the following year.
This year I grew a bush tomato called Tiny Tim in both a DWC hydroponic system and garden soil. Both started producing early and were still producing in October when we got our first frost.
Either I am a supper gardener or our understanding of determinate beans and tomatoes is wrong. I’m sure it’s the latter.
How Do Determinate Plants Really Grow?
What I find interesting about this myth is that while gardeners have been using the wrong definition for many years, botany has had it right all along.
The botanical definition of determinate is:
“plant growth in which the main stem ends in an inflorescence or other reproductive structure and stops continuing to elongate indefinitely with only branches from the main stem having further and similarly restricted growth”
This means that the main stem grows to a certain size and then the tip produces fruit (black line in the above photo). While this is happening, side branches form and these too grow to a certain size and produce fruit and more side branches. The new side branches also grow to repeat the pattern.
The net result of this growth is that the plant:
- Gets bigger and bigger all season long.
- Produces fruit all season long.
- Growth does not stop until frost.
The gardener’s definition of determinate is correct for the main stem which does stop growing and producing fruit. However, since this main stem also produces side branches the definition is incorrect for the whole plant.
If you spend some time in the right discussion groups you soon find that many gardeners report determinate plants growing according to the botanical definition and not the one used by gardeners. This isn’t the result of a few odd plants growing in a weird way. It’s the result of gardeners and garden writers not taking the time to properly understand how determinant plants grow.
Determinate vs Indeterminate vs Semi-Determinate
What is the difference between determinate and indeterminate? An indeterminate plant has a growing point that keeps getting longer. Flower clusters and side branches form along that stem. We call it a vine because it just keeps getting taller. The side branches behave just like the main stem and become vines in their own right.
Pruning tomatoes tends to hide this growth because we remove side branches and grow only a main stem or two.
A determinate plant grows to a certain height and then forms a terminal flower cluster instead of growing taller. It also produces side branches and flower clusters along the stem. These side branches also grow like the main stem and eventually end in a flower cluster.
What is a semi-determinate plant? Most definitions of semi-determinate are midway between determinate and indeterminate.
I can’t confirm the following, but I suspect people started noticing that determinate plants were not growing according to the gardener’s definition of determinate, so they invented a new category called semi-determinate. These are plants that grow shorter than tall vines and produce all summer long.
So instead of correcting the definition for determinate, people created a new myth about the existence of semi-determinate plants.
As far as I can tell the reported growth of all semi-determinate plants matches the correct definition of determinate. There really are no semi-determinate plants – they are determinate – if we use the right definition.
Are there tomato or bean plants that grow to a certain height, produce fruit and stop growing? I have not found any but if you know of some, please provide a link to the information in the comments below.
Do Indeterminate Potatoes Exist?
Lots of gardening sites talk about determinate and indeterminate potatoes, but this is another example of gardeners using the wrong definitions that then lead to confusion. For more on this see my post on Potato Towers.
Should You Grow Determinate or Indeterminate?
The main reason I grew indeterminate was to get a long harvest season, but now that we know determinates have an even longer producing season and produce their first fruit earlier, it seems as if determinate is a better option.
Another consideration is the space needed by the plants. Growing vines allows you to grow up and use very little ground space. A point for indeterminates. You also don’t have to bend as much to harvest climbers.
Some special cultivars, like my favorite Sweet 100’s are only available as vines, so I’ll keep growing them. On the other hand green beans seem to taste about the same from both bush and pole varieties.
Bush type plants are more easily attacked by our small 4 legged friends.
There is no right or wrong choice. Understand the two types and your needs, and make a decision based on that.
Are these plants annuals or are they semi perrinial? I live in Western Washington State on the SW edge of South Puget Sound. We’re usually warmer in the summer and get more snow in the winter when the snow level drops. We are SE facing and live close to a tidal bay. We don’t get enough of afternoon sun in the summer but plenty of sun all year round; often very windy conditions (growing drought tolerant plants like barberry not shielded is difficult – winds up to 60 mph in the winter).
Our golden privot, though supposed to be perrinial, is more semi evergreen and has dropped all its leaves only one winter out of four. We have an older gulf stream nandina that drops it’s leaves from cold winds or heavy snow but grows new ones within a month. Some things don’t get hot enough long enough and produce less than desired (veggies). On the other hand, I didn’t water the grass at all this summer and it only had a few brownish spots and now greening again.
Would the determinate and variations survive in my garden?
I didn’t mention the gophers carry a bacteria that some Japanese maples turn black and die. Thankfully, Iselli sells Korean/Japanese cultivars that are more hardy and bounce back (If you ever been to Taegu Korea, the climate range is 105 F down to below 0 F at night), though one of my two Sangu Kaku bounced back (I have several Japanese maples and one over forty years old).
I have several natural climate enemies that are hard to adjust for: wind, drought and humidity.
I think tomatoes are perennial, but in cold climates both are annuals.
Thank you for this. It finally makes sense!
Great discussion! I totally agree, as usually. I have noticed, as you pointed out, that the determinted type do continue to grow and produce fruit from the side branches after ( while ) the top of the plant tips off with a cluster of fruit. Thanks for your insightfulness. Cleve