To Prune or Not to Prune?

by Jack LaRue

Good morning, Pumpkinistas!

This very timely article from the July 2009 issue of the Pollinator Press, the official newsletter of the Pacific Giant Vegetable Growers (www.pgvg.org). I am a long-time member, and highly recommend joining this organization, particularly if you reside in the Pacific Northwest. Fortunately, they also accept out-of-state and international members too.

To Prune Or Not To Prune?

By Jack LaRue

Should I prune my pumpkin plants?
Why should I prune my plants?
What should I prune?
How should I prune?
When do I start / stop pruning?
Should I terminate the secondary vines?
Should I terminate the main vine?
How large shall I let the plant get?

Recently I attended a seminar on how to grow giant pumpkins. One of the speakers mentioned that he does not
prune his plants. This caught me by surprise. I wonder how many growers are not pruning their plants. His statement
reminded me of a question that Dick Wallace asked me a few years ago. Dick asked me if I wanted to grow
giant pumpkins or salad? An un-pruned pumpkin plant can grow a huge salad and okay giant pumpkins. I do not
want to grow okay giant pumpkins. I want to grow really big giant pumpkins. So what do you want to grow?
Why should we prune our plants? A plant that is not pruned soon turns into a tangled mess of leaves and vines.
The plant will compete with itself for light, food and water. A tangled plant is also much harder to maintain. The
answer is simple. Unless you want to grow salad you want the plant to concentrate most of its energy on growing
a giant pumpkin.
To prevent the plant from becoming a tangled mess it is a widely accepted practice to prune all of the tertiary
vines. Some growers will prune every other secondary vine as well. The benefit to pruning every other secondary
is less vine burying and a more open plant. An open plant is easier to maintain. An open plant also has better air
circulation which helps prevent and reduce the spread of disease. The draw back to pruning every other secondary
is less leaf surface and the lack of male flowers needed for pollination.
How should I prune? I use a pair of scissors and a bucket of bleach water or a bottle of alcohol. No not for
drinking, for disinfecting the scissors when I move to a different plant. Some growers will have a pair of scissors
or knife for each of their plants. Again this practice is to help prevent the spread of disease from one plant to another.
I like to prune early in the morning and let the plants heal for 10-12 hours before I bury vines. I compare a
cut on the plant to a cut on your finger. If you cut your finger you want to let it heal or produce a scab before you
start working in the soil. The same conditions apply to your plants. The soil is full of pathogens waiting for a port
of entry into your plant. Do not open the door for them!
The choice of pruning patterns is up to the grower. There are many patterns to choose from - only the growers
creativity is the limiting factor. To my knowledge there is no one pattern that works better than any of the others.
Growers need to plan ahead and prune their plants to fit the allotted space. The important factor here is manage the
plant and not to let it get out of control.
When should I start / stop pruning? I like to start pruning my giant pumpkin plans shortly after the main vine is
on the ground. When I stop pruning depends on the size of the plant and the time of the year. If the season is cool
and the plant is small I will let it grow until late in the season. Yes, I have been guilty of growing salad! If the
plant is large with a fruit set on the main vine out 15 feet or better, it is time to start terminating vines.
Should I terminate the secondary vines? Yes! When is up to you. The length of the secondary vines can be determined
by space or time. I usually let the secondary vines run at least ten feet before I terminate them.
Should I terminate the main vine? Again up to you. I never terminate the main vine. I may have all of the secondary
vines terminated but leave the main vine or the vine with the fruit set on it grow as long as it can. I want
the plant to concentrate all of its energy on the vine with the fruit. If that is the only vine still growing it makes
sense that the plant will send its energy to that vine.
How large should I let the plant get? At least 400 square feet or as large as the season will allow. What I mean
is get the plant as large as you can before fruit set. After fruit set you need to answer Dick’s question do you want
to grow salad or pumpkins?

Many thanks to Jack LaRue and Jim Sherwood!