In The Greenhouse: Practical Greenhouse Advice For The New Year

 

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I N this month’s column, I would like to touch upon several areas which I’m lumping together and calling “practical greenhouse advice” to be sure that growers start the new year on the right foot. Oh, and if you haven’t heard from me yet this year, Happy New Year!
Planting Density
Planting density, also known as plant population, is simply the number of plants per specified area. Usually, in the U.S., this number is in square feet per plant. If your planting density is too low, you are not maximizing the expensive real estate within your greenhouse walls and are wasting space and other resources that cost you money, such as water, fertilizer, heat, etc.
On the other hand, if your planting density is too high, you are also wasting money. How can this be? By crowding too many plants into your greenhouse, the plant productivity (yield) per plant drops. The yield over the entire greenhouse actually levels off even though there are more plants in the greenhouse.  
However, what is worse is that the costs of producing that limited yield 
actually go up. Why? The labor for growing and maintaining more plants goes up — more pollinating, more suckering, more leaning and dropping, and more picking (smaller fruit). The material costs of water, fertilizer, and sprays also increase. Furthermore, with crowded plants, the efficiency of spraying insecticides and fungicides is reduced since the foliage becomes too dense. Consequently, both insects and diseases may increase.
Now, let’s discuss the best planting density. For most greenhouse tomato growers, a density of 5 square feet per plant is ideal. So, multiply the greenhouse length times the width to get the greenhouse square footage. Subtract any area that will not be used for plants. Then divide that square footage by 5 square feet. That is about the number of plants your greenhouse can comfortably handle. Rounding is acceptable.
Cluster Pruning
Cluster pruning (or cluster thinning) does not mean pruning off entire clusters, but rather thinning the number of fruit in a cluster to a lower number than what they try to set. I’ve had newbie growers call me to express their excitement that their tomato plants are producing 15 fruit per cluster! Unfortunately, what they do not realize is that if they leave all 15 (or other high number) fruit, most of them will be too small to be marketable.
Tomato plants have a limited carrying capacity — the total yield that they can produce — that is defined by both the environment and genetics. So, for example, if a plant could produce 30 pounds of fruit under normal conditions, it could be 60 fruit that each weigh about a half pound (reasonable size), or perhaps 120 fruit with an average weight of about a quarter pound.  
Even worse, though, is that if all fruit on the plant are allowed to develop, the variability in size will be enormous. Those 120 fruit may range from an ounce or smaller to nearly a pound. Conversely, with cluster pruning, the variability is greatly reduced to the point that most fruit will fit in the 8- to 10-ounce range, which is what most of the American market looks for in a beefsteak tomato.
So, how many fruit per cluster? There are several good answers. Some growers prune to four fruit per cluster. Others prune to three per cluster. Still others alternate three, four, three, four, up the plant. All of these are much better options than letting all of the fruit mature. The effect on fruit size and marketable numbers is very positive — larger fruit, more marketable fruit, and more consistency in size.

In this month’s column, I would like to touch upon several areas which I’m lumping together and calling “practical greenhouse advice” to be sure that growers start the new year on the right foot. Oh, and if you haven’t heard from me yet this year, Happy New Year!

Planting Density
Planting density, also known as plant population, is simply the number of plants per specified area. Usually, in the U.S., this number is in square feet per plant. If your planting density is too low, you are not maximizing the expensive real estate within your greenhouse walls and are wasting space and other resources that cost you money, such as water, fertilizer, heat, etc.

On the other hand, if your planting density is too high, you are also wasting money. How can this be? By crowding too many plants into your greenhouse, the plant productivity (yield) per plant drops. The yield over the entire greenhouse actually levels off even though there are more plants in the greenhouse.  

However, what is worse is that the costs of producing that limited yield actually go up. Why? The labor for growing and maintaining more plants goes up — more pollinating, more suckering, more leaning and dropping, and more picking (smaller fruit). The material costs of water, fertilizer, and sprays also increase. Furthermore, with crowded plants, the efficiency of spraying insecticides and fungicides is reduced since the foliage becomes too dense. Consequently, both insects and diseases may increase.

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Now, let’s discuss the best planting density. For most greenhouse tomato growers, a density of 5 square feet per plant is ideal. So, multiply the greenhouse length times the width to get the greenhouse square footage. Subtract any area that will not be used for plants. Then divide that square footage by 5 square feet. That is about the number of plants your greenhouse can comfortably handle. Rounding is acceptable.

Cluster Pruning
Cluster pruning (or cluster thinning) does not mean pruning off entire clusters, but rather thinning the number of fruit in a cluster to a lower number than what they try to set. I’ve had newbie growers call me to express their excitement that their tomato plants are producing 15 fruit per cluster! Unfortunately, what they do not realize is that if they leave all 15 (or other high number) fruit, most of them will be too small to be marketable.

Tomato plants have a limited carrying capacity — the total yield that they can produce — that is defined by both the environment and genetics. So, for example, if a plant could produce 30 pounds of fruit under normal conditions, it could be 60 fruit that each weigh about a half pound (reasonable size), or perhaps 120 fruit with an average weight of about a quarter pound.
 
Even worse, though, is that if all fruit on the plant are allowed to develop, the variability in size will be enormous. Those 120 fruit may range from an ounce or smaller to nearly a pound. Conversely, with cluster pruning, the variability is greatly reduced to the point that most fruit will fit in the 8- to 10-ounce range, which is what most of the American market looks for in a beefsteak tomato.

So, how many fruit per cluster? There are several good answers. Some growers prune to four fruit per cluster. Others prune to three per cluster. Still others alternate three, four, three, four, up the plant. All of these are much better options than letting all of the fruit mature. The effect on fruit size and marketable numbers is very positive — larger fruit, more marketable fruit, and more consistency in size.

 


Greenhouse Tomato Short Course

I hope you will consider coming to the Greenhouse Tomato Short Course March 6 and 7. The Short Course is the longest running program of its kind in the U.S., now in its 22nd year. It will be held at the Eagle Ridge Conference Center in Raymond, MS, just outside Jackson, and close to the Jackson-Evers International Airport.

If you are a relatively new grower, you will learn hundreds of tips from the best speakers in the country. If you are still considering whether this business is the right one for you, the very low registration fee will be the best money you could spend to answer that question before you invest thousands of dollars.

For more information, check the website: http://greenhousetomatosc.com

See you there. 

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