Giant pumpkins are members of the Cucurbitaceae family and from the Cucurbita Maxima species. Giant pumpkin varieties include: Big Max, Prizewinner Hydrid and Full Moon to name a few but the most popular is the Atlantic Giant pumpkin variety. Giant pumpkins as with other pumpkin varieties will produce both male and female flowers and so self or cross pollination (pollen from another plant) can occur. Pollination is the process of transferring pollen from the male flower to the stigma (or lobes) of the female flower.
Many growers will hand pollinate female flowers on giant pumpkin plants to control the pollinations to ensure the genetic heritage of the seeds produced. The grower can do this by using male flowers from the same plant or from a different plant of a different seed line (still the same variety) to encourage certain characteristics produced in seeds. This also ensures that pollen cannot be carried in by a bee from a nearby pumpkin plant of a different variety but within the C. Maxima species. In this situation, the fruit would appear normal but its seeds would produce fruit that looks much different.
It is an easy task to distinguish between male and female pumpkin flowers. Male flowers are found on a smaller stem that is usually several inches tall growing directly from the vine at locations where leafs rise from the vine. Upon the opening of male flowers, you will find they contain a round tipped protrusion covered with pollen particles all around it. Female flowers, which are typically much less numerous than males, are located also at leaf junctions right near males. Female flowers are much shorter and contain roughly a grape sized baby pumpkin just below the flower. As female flowers open, below the petals is the stigma which will usually include multiple sections (this stigma can vary in appearance especially with the Atlantic Giant pumpkin variety). Both male and female pumpkin flowers will open upon maturity for the pollination process to occur. Observing and studying both flower types from formation to maturity will give you a good idea when they are about to open as they will grow in size and transition from a green to a yellowish color. Determining when flowers become mature will be key to successful hand pollination.
As you are preparing for giant pumpkin hand pollination, you will want to ensure that female flowers are kept no warmer than 85° F. Any warmer and female flowers will not likely set fruit and aborts will occur despite your best efforts. This can especially be a problem in the United States and Canada as very hot temperatures are often present in the summer time when pollination is occurring. You can cool down female flowers by placing frozen bottles of ice around the flower and concealing the area with a cloth blanket to keep coolness in.
Male and female flowers open up early in the morning, so plan to perform pollinations ideally no later than 8:00 AM. For this reason and to guard against bee intrusion (because they will wake up before you do) you must shield both male and female pumpkin flowers from insect contact. You can do this by using twist ties (like you find that seal loaves of bread) to tie shut male and female flowers. Seal up flowers the night before you expect flowers to open and apply the tie to the top portion of the flower to not harm delicate parts. Plan to use extra males maybe 3 to 4 per female flower. There should be plenty of male flowers so it should not be hard to find this many.
In the morning, when you are beginning to pollinate giant pumpkins, gather the male flowers by cutting them at the base of their long stem right off the vine. Take them to where the female flower is. Remove the twist tie from the female flower (the flower petals ideally will partially open up their on after this, if not its okay). Then take the first male flower and remove its twist tie and tear off each petal, exposing the protrusion covered with pollen, take and brush this protrusion gently all around the female stigma, cover it as much as possible. Repeat this process for at least 2 other male flowers. This theoretically should work with one male flower, but using a few more will ensure more pollen is transferred increasing the chances of a successful fruit set. Any additional male flowers can be opened like the others but instead of brushing them along the stigma (which should have plenty of pollen on it already), take a small piece of metal wire and scrap the pollen off the male protrusion and let if fall on the stigma. It is the opinion of this author and grower that brushing more than 4 male flowers on to the female stigma could cause pollen to get “brushed off” the stigma and ultimately cause harm to the flower and reduce chances of a successful fruit set. During the pumpkin pollination process, be on guard for bees as they can and will land right onto flowers as you are working if you don’t move them away.
Be sure to take note of the date you are pollinating and which plant is the mother crossed by the plant of the father. You should plan to set several fruits on your plants as some will likely abort and some may not be shaped well, this way you get to choose exactly which 1 or 2 fruits (or more) you want to grow to maturity. You will likely have several weeks to perform pollinations and it’s wise to take advantage of them to ensure you have the best possible fruit sets for the best possible giant pumpkins.
RESOURCES / REFERENCES:
Langevin, Don. (1998). How To Grow World Class Giant Pumpkins, II. Norton, MA: Annedawn Publishing.
Ed Thralls, Extension Agent II, Orange County & Danielle Treadwell, Assistant Professor, Horticultural Sciences Department, Institute of Food and Agricultural Sciences, University of Florida. Home Vegetable Garden Techniques: Hand Pollination of Squash and Corn in Small Gardens, Publication #HS1149. University of Florida IFAS Extension. Retrieved from: http://edis.ifas.ufl.edu/hs398