Pumpkin and Squash Interbreeding

A question came to me;do pumpkin & sqash interbreed ,I want to Know if I need to allow extra space to avoid hybredizing.

Some varieties of pumpkin and squash will interbreed.  You need to know the species names of the varieties you plan to grow, this sometimes takes a bit of searching!

All varieties within a species will interbreed.  Some different species will cross-breed, but usually don't because they bloom at different times.

This website gives species names of some varieties of squash:  https://www.nativeseeds.org/index.php/store/47/2/seeds/squash

It depends!
Cucurbita of the same species interbreed like mad, but you can safely plant different species like pepo, moschata and maxima side-by-side and they'll come 'true'.
I'm assuming by 'squash', you mean a zucchini-type thing? Most zucchini are pepo species and they'll happily breed with other pepos. It would be easy if all 'pumpkins' were X and zucchini were Y, but it's not that simple I'm afraid! There's lots of pepo pumpkins, but plenty of moschata and maxima too.
Basically, the only way you'll know is  the name on the seed-packet. If you don't know, it's someone's saved seed or bought seedlings, I'd be wary about saving seed as it's plenty likely to be crossed.
I've done a bit of research on this question and I decided to buy commercial seed  in the first season and decide on which species I can grow together each year.
Maybe more than you were after, but saving 'true' Cucurbita seed's not the simplest thing ever!
ludi posted as I was writing, so I'm pretty much repeating her info.

There are 4 species of squash

[li]Cucurbita Maxima[/li] This is giant pumpkins, big squash such as a hubbard
[li]Cucurbita Mixta[/li] Cushaw squash
[li]Cucurbita Moschata[/li] Butternut squash
[li]Cucurbita Pepo[/li] The normal pumpkins, Jack O Lantern for example, also yellow crookneck squash, zukes, acorn squash.

One type will not cross with another.  A butternut squash will not cross with a hubbard.  You can plant them in the same hill.

Pumpkins are a generalized name.  What is called a pumpkin can be in any of the four groups.  Looking at the same fruit, one person might call it a cushaw squash, the next, a cushaw pumpkin.

Within a group, the plants will cross.  A zuchinni will cross with a straightneck yellow.  You have to look at the name of the seed.  Same species will need to be spaced by distance or time.  If you don't have the name of the cultivar available, give them some space.

This thread made me curious, so I looked up my favorite, the Japanese Kabocha squash, which is a variant of Buttercup squash.  It appears to be maxima.

Somewhere I have a chart about which will hybridise with which - I'll dig it out later!  From what I remember, if you only grow one type from each species, you'll generally be fine. 

But some will pollinate others *without producing seed* - I had some 'empty' butternuts (moschata) that had been pollinated with a pepo, which had caused the pumpkin to grow without producing any seed.  Also I think you can pollinate cushaws (argyosperms) using pollen from a butternut (moschata), but not the other way around. 

But in any case, you can always hand pollinate the female flowers with appropriate pollen and then seal them up to prevent contamination.  Just be sure to find a way of identifying your 'pure' fruit so you don't mix the seed up later.

I've been collecting 'useful' photos of the various species, their leaf shapes, and the flowers, hopefully so that people can learn to tell the species apart from their leaves and figure out which flowers are male and which are female.  Here's a link to my pumpkin album for anyone who wants it.

I've dug out my copy of The Perfect Pumpkin by Gail Damerow, and she says that while the different species don't readily cross, they  can do sometimes.  I guess if you are short of insects early in the season and resort to hand-pollination, like we did, then the following might be helpful to know...

Maxima can be pollinated by moschata, or rarely by argyosperma or pepo. 
Argyosperma can be pollinated by moschata.
Moschata can be pollinated by maxima or pepo.
Pepo can be pollinated by argyosperma or moschata, or rarely by maxima.

Without any pollination, the fruit will abort, as far as I know.  We ended up with some butternuts (moschatas) that were 'empty' of seeds and never developed that nice big bulbous butt end - presumably we'd used a pepo to pollinate these with.  And there were also some cushaws (argyosperma) that appeared fully developed but were solid flesh all the way through, with no seeds and no cavity.  My other half wasn't sure if he'd used pepo or moshchata to do the pollinating, but we're going to experiment again next year as having all that flesh with no seeds to cut out wasn't a bad result.  We also had some with just a very few seeds in - we're not sure if these are moschata/argyosperm cross or if it had been pollinated by both types but only the 'pure' argyosperm seed developed.  Maybe we'll know next year when we plant the seed and see what sort of fruit develops... 

In my greenhouse I once planted several cucumbers and one giant pumpkin plant. Come halloween the kids and I were carving in the kitchen and all of a sudden we smelled cucumbers! The inside of the pumpkins were solid, like a cucumber, and smelled like a cucumber!

In my current garden I have left several different squash and pumpkins overwinter. This year I am getting all sorts of different sqash and white pumpkins. Even though I started with patty pans, zuchinies , butternut and pumpkin.

Burra Maluca wrote:

But in any case, you can always hand pollinate the female flowers with appropriate pollen and then seal them up to prevent contamination.  Just be sure to find a way of identifying your 'pure' fruit so you don't mix the seed up later.

I think this is the most 'safe' way to go.  Tape or bag male and female flowers the day before they open to prevent cross-contamination.  Hand pollinate wth a soft brush and reapply the tape or bag for another day or two.  Make sure to mark the hand pollinated flowers with a twist-tie or some other kind of flag so you can keep track of them as the season progresses

Thanks for the info.

Besides saving seed for planting, I was never quite sure what to do with squash seeds (again, my favorite, kabocha).  I always thought I should save and eat them, but would never get around to it.  One day I was steaming squash and left a couple of seeds in by accident, and they were delightful steamed, so ever since we just cut the squash and put it in seeds and all and eat the seeds with the meal.