How to tell when to pollinate a female giant pumpkin blossom

Another gardener friend, Mac asked me a great question about the female flower and the timing of the pollination so I thought I’d give you all some more info.

When you spot a female pumpkin blossom that you want to hand pollinate later, you need to watch it daily as it grows.  The optimal position of a female flower will be on the main vine and at least 10 feet out or longer although I did pollinate one this year at 8 feet out for insurance in case no others ‘took’. I will also pollinate every female flower on the secondary vines that grow out from the main vine on the sides. This is all for insurance in case something happens to the best one. Later, after I feel confident which one of these pumpkins is growing the fastest, I will cull all but the first and second fastest growers. So each plant I care about, will have 2 giant pumpkins growing on them. The first and a backup.

Here is a female blossom NOT READY. The blossom is still very green although getting larger.

Here is a female blossom that will be ready to open the next morning. So how do I know when the female blossom will open? I watch the female blossoms closely (they are the ones with the baby pumpkin attached to the base of the flower. I always look for the blossom to get big (still closed) and then the day before, the blossom will get the slightest hint of yellow green on the tip. That’s when I know it will open the next morning. Works everytime. I cover the female flower the night before after the color change and get out in the patch early the next morning.

We have 4 hours from the time the blossom opens which is always first thing in the morning. This is usually between 6am -10am. So I cover the female flower the night before with a piece of row cover and get out in the patch early before the beez take all the pollen from the male flowers. Many times I cover three male flowers that will be ready the next day as well  (they haven’t opened up but look like they will the next day) so I have lots of pollen on them. The beez get out early too and will take it all of their pollen if not covered.  The pollen is food for the bees. It is protein for them. Beez will go after the nectar and the pollen on these plants. I’m sure the beez are attracted to the big blossoms and wonderfully sweet smell the blossoms emit. Someone should make a perfume out of this smell-it is wonderful. What would that be? Parfum de fleurs de citrouille (scent of pumpkin flowers)!! If I know I’m pollinating, I will get up early. Generally between 6-8 am is when I pollinate them but I have forgotten sometimes and ran out at 10 am to pollinate.

Then after pollination be sure to close up the female with a twistie tie or piece of string for 24 hours as shown here. After 24 hours, you can let the flower open up cause it will either be successful or not and you won’t know till after at least day 10 (that is the benchmark) if it was successful. The female flower shrivels up and drops off (like an umbilical cord) and the baby pumpkin will get larger and larger. If the pollination didn’t take it could be because of several reasons. One reason is because it was too hot the day of pollination (over 90°F). This might cause some pumpkins to abort later. The second reason is because we didn’t get enough pollen on the stigma part of the female blossom. Either way, you’ll see the pumpkin start to grow and then suddenly stop. It looses it shininess, getting duller and softer and usually spots show up as it decays which is a self abortion.  If this happens, cut it off. That is why we pollinate more than we need because sometimes the plant self aborts its babies if something is wrong-kind of like a miscarriage for us.

How to pollinate a giant pumpkin

Here are pictures on how I hand pollinate a giant pumpkin…

Here I’m getting ready to pollinate a giant pumpkin. I’ve gathered several male flowers that are  by my shoe. I have one in my hand ready. I try to use several male flowers to make sure I get enough pollen on the female flower. Notice the female flower just below my hand that is open and ready to be pollinated.

Here is a closeup of the male flower. The ants can be accidental pollinators too.

Here is a closeup of the female flower. When she opens up first thing in the morning, she is ready to receive pollen.

Here I’m peeling off the flower petals from one of the male flowers. I peel off the petals so only the stamen is left. That way it can get to the female stigma.

Here is the male flower with all the petals off.  Notice the pollen on the stamen and around the base.

Now I take the male stamen that is loaded with pollen and use it like a paintbrush to paint the pollen all over the female stigma. then I repeat with the extra male flowers.

Then I tie and close up the female flower so it can’t accidentally get pollinated by the beez. It will stay closed up for one day and then I will untie it as the female blossom will only acept the male pollen for about a 4 hour period. If you want to know who are the parent pumpkins, this is the way to control the assurance of the genetics. We try to get bigger and better pumpkins each year which is why we hand pollinate.

Giant Pumpkin Sex 101a

Ok, here’s the skivvy on giant pumpkin sex 101. I’ve been talking about giant pumpkin pollination a lot and have been giving bits and pieces of info and so want to be clear about WHY we choose to pollinate them and HOW we hand pollinate giant pumpkins.

First WHY do we pollinate them?

If I was growing regular pumpkins I wouldn’t pollinate them, I’d just let the bees do it but giant pumpkin growers want to know what genetic material is being passed from the male flower to the female flower of a pumpkin. why? Because it doesn’t affect this season’s pumpkin, but the next year’s seeds of that pumpkin. That way we can grow bigger pumpkins,  prettier pumpkins, oranger pumpkins, rounder pumpkins, etc. next year. If we let the bees do it, we wouldn’t know which pumpkin plant the pollen came from as the bees visit many flowers from many plants.

So we grow several different pumpkins from seeds from different giant pumpkin growers. For instance, I have 3 growing right now and one that I hand pollinated  the other day was from the seed of a 895 lb pumpkin seed grown by a grower named Grande in 2009 (hence it is called an 895 Grande 09) and I crossed that female flower with the male flower from a seed of a 945 lb pumpkin seed grown by a grower named N. Harp in 2010 (hence it is called 945 N.Harp 10). Why would I do it? I’m trying to cross 2 top notched pumpkins and see what I can get. I hope to get a round really orange pumpkin with great weight. The 895 Grande was really pretty but the 945 N. Harp came from great genetics. I know which pumpkins they came from because those growers list that with their seed. I can also look up the grandparents as well. If we let the bees do it, we would not have this information to help us decide.

Second question is HOW we do we hand pollinate the female flower?

male flower side view

female flower side view

First all pumpkins produce both male and female flowers on each plant. The male flowers show up first and then the female flowers start showing up. I watch the closed green female flowers closely for when they start to get big and slightly yellow orange on the tip of the flower but the flower is still closed. When I see that, I know it will OPEN THE NEXT MORNING. So I cover it the night before  and  some male flowers as well so the bees won’t get to it first with unknown pumpkin pollen. Then I get up EARLY the next morning as we have a 4 HOUR

male flower inside with stamen

female flower inside with stigma


FLOWER, (GENERALLY 6-10AM) and find some newly opened MALE flowers (or uncover the ones from the night before) from the plant I want to cross the female flower with. It could be from the same pumpkin plant or a different one. Now remember we can tell the female flowers because it looks like a little pumpkin is attached at the base of the flower while the male flowers are on skinny stems only. See pictures. Also the inside of male and female flowers are different and when the flowers are open you can see the differences. Male flowers have stamens  (kind of look like a penis-I told you we would talk sex) that have the pollen on it which looks like grains of powder all over it. The female flowers have a stigma (think vulva) and if the timing is right (remember 4 hour time period) will accept the pollen from the male flower.

male flower with petals peeled off revealing the stamen

So as a giant pumpkin grower I take a male flower and peel off the petals leaving the stamen and take that flower and brush the stamen loaded with pollen like a paintbrush on the inside of the stigma and also around the outside of the stigma as well. Then I close up the female flower with a twistie so no other pollen can get in. I keep it closed for one day and take off the twistie afterwards and wait to see if the pollination takes which could take quite a few days. Sometimes they abort when they are a little smaller than the size of a basketball.

male stamen pollinating female stigma like a paintbrush

Inside each female flower are many immature eggs waiting inside immature seeds holding half the genetic material. The pollen holds the other half of the genetic material. If the female receives the pollen, the pollen will germinate and move down inside the stigma to the egg within an immature seed and fuse its genetic material with the genetic material of the egg stored  in that immature seed inside that tiny pumpkin. PRESTO! FERTILIZATION has taken place. Every egg fertilized becomes a a viable future seed. And every seed fertilized holds the genetic material for a future pumpkin If not enough pollen as passed, the baby pumpkin will self abort. (or if it is too hot-90 degrees or hotter, they can abort too) COOL, HUH?!  The so next time you need to talk to your kids about sex, you can talk pumpkin sex as an example!

Ok, have I given you too much info? I figure this way we won’t have to go over this again.!

giant pumpkin flower pollinated!

945 N. Harp 5 segment stigma

So the 945 N. Harp pumpkin flower that I said was almost ready to open, did this morning as pictured above. That was really fast to open. So I got some male flowers off the same plant that had pollen and broke them off, stripped away the petals and used them like a little paintbrush to go all around the outside and also inside the stigma. Notice this stigma has 5 segments. Most big pumpkins have 4 or 5 segments and some have 6 but many of the six segment ones abort due to insufficient pollination.

female flower with male flowers around it after hand pollination

The next picture is of the flower after I hand pollinated it with the ‘spent’ stamens in front of it. I almost feel like smoking a cigarette!

The last picture is where I closed up the flower with a twistie tie so the bees won’t accidentally pollinate it with another pumpkin’s pollen. By controlling pollination, I try to control (somewhat) what the future seeds of the pumpkin will be but it won’t affect this year’s pumpkin and what it will look like only it’s seeds.

pollinated giant pumpkin flower closed with twistie

I will cross pollinate some of the other female blossoms with some of my other pumpkin plants to see what the next generation’s seeds will produce next year. But this one I self pollinated it. So on the same pumpkin plant you could have some pumpkins that were self pollinated and others that were pollinated with other pumpkin plants.

Pumpkin female blossoms!

945 N. Harp female blossom almost ready to open-tip turning yellow

Last week I saw a bunch of male flowers, still small and closed but no female flowers. Yesterday I saw some baby female flowers with their baby fruit attached. Yea! Finally!

945 N. Harp female blossom not ready to open-blossom green

Yesterday I noticed the female blossoms are still small and closed but the male flowers are now blossoming and ready for the girls! There are two female blossoms on the main vines and 7 more on secondary vines. The picture on top is almost ready to open as the blossom is just starting to turn a subtle yellow color on the tip. In the other blossom pictures in this post, the blossoms are still very green and will open later. I will pollinate all of them when they are ready and see what I get.

895 Grande female flower

Look how different the shape of the baby pumpkins are on the different pumpkin plants! The 945 N. Harp pumpkin flowers have round little pumpkins attached and the 895 Grande pumpkin flower has an oval shaped pumpkins attached. I think that is so cool that you can start to see the future pumpkin shapes even on the blossoms.

Even though the blossom looks like it has a baby pumpkin attached to it, it still needs to be pollinated which happens after the flower opens. Some will abort if pollination is not complete or if the weather is too hot. I hope the females open this week as the weather is suppose to be perfect for pollination-80’s all week. Not too hot. Anything over 90 is problematic for pollination.