Pumpkin Pollination Information

[I wrote this explanation for one of my kids' schoolmates.]

So you have some Atlantic Giant pumpkin plants growing and have a question on how to pollinate the flowers to get pumpkins.   I'll explain... there are 2 different kinds of flowers, and both kinds occur on one plant.   There are male flowers, and female flowers.   Only the female flowers may develop into pumpkins.   The males never will.   Here are some pictures so you can see the difference.   As a plant is growing, it first develops male flowers only.   They will open and die without being of much use (they only last 1 day each).   Shortly (another week or so), the plant will grow and mature a bit more and start to have female flowers as well as males.   The females are usually further out on the vine.   By the first week in July, you should be close to having female flowers if you don't have them already.  

Male Atlantic Giant Pumpkin Flowers Male Atlantic Giant Pumpkin Flowers

In the picture, look at the flowers in the coke can plus a flower sticking out of the top of a fence post.   These are male flowers.   Notice the straight green stem ends, and petals just begin.   I peeled some petals back so you can see inside- there is just one large stamen holding pollen, with cool ridges in it that kind of looks like a brain.   (I think it actually has another name on a pumpkin flower, not being a true stamen, but it is essentially a stamen, generating pollen.)   Look at some pollen with a magnifying glass or microscope- pumpkins have some of the largest pollen grains of any other plant.   While it looks like dry yellow dust if you get it on your finger, you'll see they are really moist looking spheres. Look at the ridges too.   The ridges split open in the morning when ripe to release the pollen inside each ridge.  

Female Atlantic Giant Pumpkin Flowers Female Atlantic Giant Pumpkin Flowers

The other picture has 2 close ups of a female flower.   I've peeled some petals off so you can see what's inside.   Notice the swelling at the top of the stem- a "baby pumpkin" just below the base of the flower petals.   The inside of the flower looks different too, with a pistil having usually 4 or 5 segments, called lobes on pumpkins.   Each lobe will grow to be a separate grouping of seeds within a pumpkin.   Your pistil may not look quite this defined or have any white showing- the segments may be squished together more than the flower I have in the picture, and will probably be pure yellow.   The female flowers open very early in the morning, perhaps about sunrise.   If you look closely, you can tell when a female flower will be opening the next morning because the normally green petals will develop a yellowish tinge in the evening, around supper time. The yellowish ones will open tomorrow morning, the green petaled ones will open some other, later day.   Same thing with the males- when the petals get yellowish in the evening, you know they will open the next morning.   You will want to protect the blossoms of a few male flowers in the evening around suppertime by tying a plastic bag around each of them so that when it opens the next morning (early, while you're still sleeping), the bees won't steal all of the pollen before you get to it.   The bees can't get through the plastic bag. By 9 AM, all the pollen from the unprotected male flowers will surely be gone- taken away by the bees.   That's why I suggested protecting the ones you want to use.  
To hand pollinate a female pumpkin flower, you need to pick or cut off a few fresh (just open today) male flowers (1, 2, 3, or 4).   Picking them won't hurt the plant. Day old flowers (male or female) will not work for pollination.   Peel the petals completely off, leaving just the single stamen with the stem attached (to hold onto).   Take the male flower over to a freshly opened female, and gently brush and rub the stamen all over the top of the pistil in the female flower, to rub off the pollen.   You may not be able to see much happening, because everything's yellow, but it will work.   You can use a few male flowers (if you have them) for each female to increase the chance of pollination.   You don't have to get up at the crack of dawn to pollinate the flowers- I usually sleep in and do it anytime between 7:30 and 9 AM and it has worked just fine.   You can tell if your pollination worked after a few days by looking at the female blossom.   The petals will be droopy and dead looking (eventually falling off)- but that's normal- the flower itself only lasts 1 day.   If the "baby pumpkin" at the base of the flower looks dull colored, and hasn't grown in size, it's dying, and the fruit did not "set" (the pollination didn't work).   Sometimes this happens even if you do everything right. If it does, don't worry, as there will be plenty more female flowers soon.   If the baby pumpkin looks shiny, and has increased in size, then the pollination worked, and a pumpkin is now growing there.   You can fertilize the plant with Miracle Gro plant food per the directions on the package and everything will grow bigger   (you won't notice it right away, but it will help).  

If you have any other questions, I'd be happy to help!

For more pumpkin growing info, here's some more advice:
60-second guide to growing giant pumpkins