Re: The Doucet Theory on Pumpkin’s with SplitPersonalities
Diana,
Will you marry me?
Greg
Diana Doucet wrote:
> I have a theory on a leading cause of sag lines (Dill Rings), blowouts
> and splits in large pumpkins that occur in maturing fruit mid to late in
> the season. These problems usually lead to catastrophic failure of the
> fruit. Since we are now upon the season that these types of problems
> occur, it is a good time to throw my theory on the table for discussion.
>
> First a little background. When a pumpkin is small, it is solid
> pumpkin meat. As it grows, a large cavity forms in the interior of the
> fruit. This cavity is filled with air, seeds and pumpkin guts. By the
> time the pumpkin is mature, air comprises a significant percentage of
> the interior cavity.
>
> Did you ever wonder how air gets inside the pumpkin? There are no holes
> in the fruit to let the air in as the pumpkin grows and the interior
> cavity expands in volume. The answer is that air must permeate the
> shell at some measurable rate and fill the cavity as the pumpkin grows.
>
> How quickly air can permeates through the pumpkin shell probably varies
> somewhat from pumpkin to pumpkin depending on the thickness and density
> of the shell. As the pumpkin grows, the rate air can permeate probably
> increases as the total surface area of the pumpkin shell increases. The
> rate that air permeates probably also increases in a proportional
> fashion to increases in the pressure differential between the outside
> and the interior of the pumpkin. (Are you following all this?)
>
> A pressure differential between the interior and the exterior of the
> pumpkin will occur if the fruit has a sudden growth spurt and the cavity
> expands faster than air can permeate through the shell into the pumpkin.
> A pressure differential would also result from rapid changes in the air
> temperature within the interior of the pumpkin or to a lesser degree
> from abrupt changes in atmospheric pressure.
>
> All this discussion on pressure differentials is leading to my theory so
> please bear with me. When I was in high school, we did an experiment in
> science class where we heated a gallon sized metal container and then
> tightened the cap on so that it was airtight. We then let the container
> cool. As the air inside the can cooled, it contracted. The container
> slowly collapsed in upon itself as if an invisible hand was crushing it.
>
> As the air contracted, it created a pressure differential between the
> inside and outside of the can creating a crushing force on the can. A
> pressure differential of just one pound per square inch (psi) could
> create a crushing force of two hundred pounds on the can because the
> surface area of the can was about two hundred square inches. (Multiply
> the pressure differential in psi times the surface area of the container
> in square inches to obtain the total crushing force.)
>
> If we now talk about pumpkins and think of them as large sealed
> containers filled with air like the containers in my old experiment; a
> similar process is at work on a daily basis. The air pressure on the
> outside of the pumpkin is atmospheric pressure, which is relatively
> constant regardless of temperature. The air inside the pumpkin is
> heated during a hot day expanding the air inside the pumpkin and
> increasing the internal pressure on the shell walls. If the air expands
> enough, the pressure in the pumpkin will exceed the outside pressure and
> air will start permeating slowly out of the pumpkin cavity. At night,
> as the air in the pumpkin cools, it contracts creating a negative
> pressure differential between the inside and the outside of the pumpkin
> and a crushing force on the shell walls. The pumpkin also grows during
> the night, increasing the cavity size and magnifying the crushing force
> on the shell walls. Air slowly permeates into the pumpkin to relieve
> this pressure but remember this is a slow process so the pumpkin acts
> like a sealed container with a very slow leak in it.
>
> A pressure differential of just a pound per square inch in a large
> pumpkin could result in a crushing force of over a thousand pounds being
> exerted due to the large surface area of the pumpkin shell. Just think
> of five big guys sitting on your pumpkin drinking beer!
>
> This brings me to my Theory.
>
> The Doucet Theory on Pumpkins with Split Personalities – Expansion and
> contraction of the sealed pocket of air inside the pumpkin is a major
> culprit in shell integrity disorders.
>
> This theory leads to a host of possible failure modes:
>
> The constant mechanical cycling of the shell, as the air inside the
> pumpkin warms and cools on a day to day basis, causes weak areas in the
> shell structure to wear down and eventually fail. Splits along a rib
> seam where the shell is the thinnest or a blossom end split would be
> possible examples of this type of failure.
>
> A large negative pressure differential caused by rapid cooling of the
> internal air and/or a growth spurt would cause a significant crushing
> force on the gourd as discussed above. If the crushing force becomes
> too great, it will cause the shell wall to collapse catastrophically and
> split internally. An internal split perpendicular to the ribs would
> cause a sag line (Dill Ring). An internal split along a rib seam might
> manifest itself as a weak area and become a hole if it reaches the
> surface of the shell.
>
> A large positive pressure differential caused by rapid heating of the
> internal air will blow the pumpkin up like a balloon and could cause a
> blow hole in a thin area of the shell or external split in a weak area.
>
> I’m sure that other factors cause the pumpkin shell walls to fail. Just
> the weight of the pumpkin shell itself and how it is supported by the
> ground and stressed by the stem could cause the shell to fail
> mechanically and split. Also uneven growth in the shell walls could
> cause internal stresses that eventually result in structural failure.
> But, I believe expansion and contraction of the sealed pocket of air
> inside the pumpkin is a major culprit in shell integrity disorders.
>
> This theory suggests that steps to minimize the rapid heating and
> cooling of the pumpkin should be taken. Shading should be provided
> during the day and the pumpkin should be covered with a blanket at
> night. It is also important to avoid growth spurts caused by the uneven
> application of water or fertilizer.
>
> Since I have never seen this idea posted or written about before, I’m
> seizing the opportunity to take credit for it. I would like it if
> anyone of you out there tried to poke holes in my theory or had any
> comments. Until you prove me wrong, don’t temperature cycle your
> gourds.
>
> diana
>
> 3rd year grower
> best 587 est. 1999
> zone 9, SF Bay Area, CA
>
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