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Growing Giant Pumpkins - A Getting Started Guide
SOIL PREPARATION: Minimum space is approx.
400 sq. ft. per pumpkin plant. Twice that space or even more would be an advantage, and will generally result in larger pumpkins.
Prepare the soil by cultivation. Rake out larger stones, clumps of sod. etc. Incorporate into the soil an inch or more of
organic matter in the form of compost. aged manure, peat moss, leaf mold, or rotted straw. Adjust pH to 6.0 - 7.0. Prior to
planting, broadcast a balanced organic or commercial granular type fertilizer, and work into the soil.
STARTING SEEDS: Start seeds in 4" peat
pots about May 1-10 depending on local conditions. The tendency is to start too early, which generally works against the grower.
The plants will need warm soil and settled weather to grow well. Giant pumpkin seeds germinate best at 80 - 95 degrees F.
Germination will be slow and may fail at cool room temperature of 65 - 70 degrees F. A commercial propagation mat may be used,
or a warm microenvironment found. Some examples would be:
Over a hot water tank, in the oven with just the light on, in a cooler chest with warm bottles of water inside,
on a mantle near a stove, etc. Excess heat is to be avoided.
Seeds may be pre-spouted between moist towels to 1/4" root protrusion and then planted one to each 4" pot, rooted
side down and 1/2" soil over the rounded end.
TRANSPLANTING: After 2 - 5 days transplant
potted plant to prepared growing beds. Protect young seedlings with properly ventilated cloches or minigreenhouses.
Water as necessary to avoid heat stress or wilting. When
well established cloches may be removed. Wind protection may be needed until plant is well anchored with vines on the ground.
Mound soil over vines at several leaf axils to stabilize plant and to encourage secondary rooting from the vines. Water as
needed adding balanced soluble fertilizer to water once per week. Control weeds with mulching, shallow cultivation, and hand
weeding as necessary. Remember, shallow roots may extend 4 ft. or more out from perimeter of the plant.
FRUIT SET: The plant should blossom and
set fruit between July 1st and 20th. Male blossoms will appear first. Males are on long stems with a rod like structure inside
the flower. which is coated with pollen. The first open male flowers will be towards the center of the plant. Female flowers
are on a short stem, and have a small round yellow pumpkin behind the flower. The first female flower to open will be out
from the center of the plant on one of the vigorously growing vines. In the absence of bee activity or to get an earlier set.
the grower may hand pollinate a newly opened female blossom with several of the fresh male flowers. Pick several newly opened
male flowers and tear away the yellow flower portion, exposing the pollenbearing stamen. Leave part of the stem to use as
a handle and gently roll the pollen from the males onto the stigma in the center of the newly opened female blossom. Depending
on temperature and weather " is generally done from earlv to mid morning. Males from the same plant as the female to be pollinated
may be used (self-pollinated). However, for best quality, it is best to use males from a separate and not closely related
plant. (cross pollinated). The plant must be large enough to support a fast growing pumpkin: therefore setting a fruit too
early can have a negative result. The plant should have a minimum of 100 - 150 leaves before a pumpkin is set.
PRUNING : To avoid rampant crossing vine
growth, it is advisable to trim and prune. Generally 3 - 5 primary vines are allowed to grow out from the center of the plant
in different directions. Side vines will develop on each of the primary vines, alternately at each leaf. The side vines are
allowed to grow, but are trained away from one another or pinched back before they cross. These side vines would in turn produce
their own set of vines alternating at each leaf. This third set of vines (tertiary vines) is removed from each secondary vine
when they are small or in the bud stage. This results in a more open plant with better air circulation. which can help prevent
disease problems. A pumpkin can be set on each of these primary vine structures. After 2 - 3 weeks select down to the best
2 pumpkins.
STEM STRESS: Stress or tightness can develop
where the stem of the pumpkin attaches to the vine. The vine must lift off the ground. as the pumpkin grows taller. The vine
will be rooted to the ground on the under side. These roots must be severed several feet each way form the pumpkin. Also as
the pumpkin grows, the shoulders of the fruit on the stem end may contact the vine and create stress. This usually happens
on the side away from the center of the plant. The pumpkin may be moved very slowly, 1 inch per day, until it is at a 90-degree
angle to the vine (both shoulders equal distance from the vine on each side of the stem).
Never move the pumpkin early in the morning as the stems
and vines are brittle when it is cool. Adjustments should be made a little at a time in the afternoon, starting when the pumpkin
is approximately basketball size. It is helpful to have the pumpkin growing on the outside of a curved section of the vine.
In this way the pumpkin will have more room to develop without pushing on its vine. The vine can be manipulated at the time
of fruit set. Set the female blossom on the outside of a curved section of the vine. Stem stress symptoms can develop very
quickly with a fast growing pumpkin. The vines near the pumpkin should be checked frequently for tightness. When the pumpkin
grows taller, several feet of vine will be supported by the stem of the pumpkin in both directions. It is helpful to support
the weight of the vine with blocks of Styrofoam or other material in order to take stress off of the stem.
SHADING: When the pumpkin is small, the
leaves of the plant will shade it. When the pumpkin grows larger, shade should be provided. Shading reduces the aging stress
of direct sunlight on the tender skin of the fruit, and allows the shell to expand and stay flexible longer. Shading also
reduces the internal temperature of the pumpkin, reducing the threat of rotting or splitting.
SPLITTING OR CRACKING: Each year many
large pumpkins split or crack while growing at a rapid rate. We walk a fine line. The grower wants his pumpkin to grow as
fast as possible in order to reach a large size, and as a result may step over the unmarked line (sustainable growth curve).
Some seed stocks are more at risk than others, especially those with genetic potential to produce pumpkins over 700 pounds.
Factors which may help to avoid splitting, include:
1. Try to grow your pumpkin at an even moderate pace
over the entire season
2. Try avoiding large doses of fertilizer and water
at critical phases of the pumpkin growth cycle.
3. Try having a high level of organic matter and an even concomitant moisture level to help moderate and buffer
against growth spurts and stops.
Multiple fruits on a risky cultivar may act as shock absorbers, spreading a surge in uptake over two or three
pumpkins. Applying a fungicide and reducing water and fertilizer to the plant can manage minor cracks. Stem splits often appear
much worse than they are. The stem is hollow and may split all the way through and tear into the flesh of the pumpkin a small
amount. Sometimes this releases the stress allowing the pumpkin to develop. Treat all wound sites with fungicide, allow for
good circulation, and keep the area dry. Occasionally a stem split or a surface crack will continue to expand and deepen until
the seed cavity is breached. Once the seed cavity is exposed to the outside atmosphere, the pumpkin is no longer a viable
candidate for competition. No effort should be taken in regards to plugging or patching, as the pumpkin will rot from the
inside out.
PESTS AND DISEASE: Problems vary widely
from region to region. In the Northwest, giant pumpkin plants are relatively free of pest and disease problems.
Sometimes black aphids appear on the undersides of the leaves later in the season. Aphids can spread the mosaic
virus, but this hasn't been a major problem for Northwest growers. It is best to contact an experienced local grower for specific
problems in a given area. Information may also be available trom County Agricultural Agents and garden centers in regards
to insect or disease problems affecting pumpkins or squash in region. Where vine borers and cucumber beetles are present.
plants may need preventative action before pests are active
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