Mysteries of Cross-pollination Between Vine Crops

This will deal only with plants that produce crops that may be commonly called one of the following:  squash, pumpkins, or gourds.  None of them are known to cross-pollinate with melons or cucumbers.  My interest was piqued when Paul Dickens gave me some saved seeds for storage squashes/pumpkins and I planned to grow all of them, believing that none of them would cross-pollinate with the others because they were of different species.  I also bought one packet of Green-striped Cushaw squash seeds from Pinetree Garden Seeds to plant because they were a different species from the ones Paul gave me, and I remembered my mother growing them.  The seed packet had the Latin species name wrong IMHO, and I wrote customer service to ask about it

My plans took on major complications when I got a reply from a customer service person at Pinetree Seeds who referred me to the website linked below. The packet was indeed mislabeled.  It's the only familiar squash in that group, and the group used to be called mixta and is now called argyrosperma--never pepo.  But the other part of the reply opened a can of worms on which I've just now slammed a lid.  The contact person also told me that ALL the squash-pumpkins-gourds cross-pollinate. Woah!  She should have added [with something else], because it's not quite correct to say that everything cross-pollinates with everything else.  Sorting it out took me way too long, and I'm posting it here so that I'll never need to do it again, and so that others might benefit. 

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 Cross-pollination of Cucurbitae

https://www.morningagclips.com/the-complicated-world-of-cross-pollination/

I had hoped to plant all of these storage squashes together without fear of cross-pollination (because they belonged to different species of the Cucurbitae genus), but realize now that I need to do some regrouping:  

1.  Maxima  (Queensland Blue--stored till May for Paul)

2.  Argyrosperma (formerly Mixta, Green Striped Cushaw)

3.  Moschata  (Neck Pumpkin, AKA known as Dutch Long Neck, like a giant butternut)

4.  Pepo  (Tarahumara--Southwest Indian Winter Squash--drought tolerant, and the best one of all for Kansas, according to Paul Dickens' experimentation last year, pick at 90% green stage, stores for 6-12 months)

From the website:

"Focusing on the Cucurbita genus, there are 4 groups of primary interest:

1.  The maxima species, which contains winter squash, buttercup squash, banana squash, and some pumpkins*
2.  The argyrosperma species (formerly known as mixta), which contains the cushaw pumpkin [please note that no other member of this species is commonly grown].
3.  The moschato [sic] species, which is the butternut squash group
4.  The pepo species is a large group containing summer squash, acorn squash, most of the pumpkins, zucchini and spaghetti squash."  

*I'm adding North Georgia Candy Roaster to this list since it was highly recommended by Barbara Pleasant, one of my favorite garden writers.  It is a banana type.  I have not delved at all into which categories that individual pumpkin varieties belong to.  

Main takeaway from website:  " . . . [P]epo can cross with argyrosperma and moschato [sic], and moschato [sic] will cross with maxima."

Personal Notes on Main Takeaway:  

All of this information is relevant only if you want to save seeds from what you grow, and if you want the crops grown from saved seeds to be like last year's crop (the one from which you saved seeds).  

First Group which will cross-pollinate: (Pepo, Argyrosperma, Moschata)

--Zucchini and most summer squash (yellow crookneck, scallop/pattypan) are pepo. Some winter squash are also pepo (acorn squash, most pumpkins, and spaghetti squash).  1.  Seed saving is not recommended when any two of the pepo are grown close together.  To summarize, don't grow any summer squash, spaghetti squash, acorn squash, or most pumpkins in the same vicinity if you want to save seeds.  This is not new information to most of us--especially as it relates to summer squash.  

2.  What is new for some of us is that we shouldn't grow anything in this pepo group with Cushaw (Argyrosperma).

--Cushaw with the Butternut  squash group would be a problem too.   Green-striped Cushaw and Neck Pumpkin, for example.

Second Group which will cross-pollinate: (Moschata and Maxima)
A parallel to thinking of Moschata as the butternut squash group is that Maxima may be thought of as the ButterCUP squash group--which contains many pumpkin-shaped fruits, but also some banana-shaped ones.

1.  Don't plant together any two from the same group if you hope to save seeds.  This is not new to most of us.

--Avoid planting butternut squash and neck pumpkin (both Moschata) together.
--Avoid planting North Georgia Candy Roaster, Banana Squash and Queensland Blue Squash together (all Maxima).

2.  Seed saving is not recommended when Moschata and Maxima are grown together.  What follows may be new to some of us:

--Avoid planting butternut squash or neck pumpkin (both Moschata) with North Georgia Candy Roaster, Banana Squash or Queensland Blue Squash or any Buttercup squash and many pumpkins (all Maxima).

GREEN LIGHT ON THESE COMBINATIONS:

1.  Pepo (big family!) and Maxima (Buttercup and banana types, and some pumpkins) CAN be combined because they will NOT cross-pollinate.  Examples:  

A.  Tarahumara (pepo) and Queensland Blue (maxima)

B.  Tarahumara (pepo) and North Georgia Candy Roaster.(maxima). 

2.  Argyrosperma (Green-striped Cushaw) and Maxima can be combined.

A.  Cushaw (argyrosperma) and North Georgia Candy Roaster or banana squash (Maxima) can be combined.

B.. Cushaw (argyrosperma) and Queensland Blue (maxima) can be combined.

Final simplification for my purposes:

Of my original selected storage varieties, It WILL work to plant one of these combinations if I plant none of the others nearby:*

A.  Tarahumara (pepo) and Queensland Blue (maxima)

                      or

B.  Tarahumara (pepo) and North Georgia Candy Roaster (maxima)

                       or

C. Cushaw (pepo) and North Georgia Candy Roaster (maxima)

                       or

D. Cushaw (Argyrosperma) and Queensland Blue (maxima)

*It would also work to plant any summer squash (pepo) with a maxima (like Queensland Blue).  

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It will NOT work to plant Neck Pumpkin with any of the other storage squash because it is a Moschata, which will cross-pollinate with pepo (Tarahumara), argyrosperma (Green-striped Cushaw), and maxima (Queensland Blue).  

It also will not work to plant neck pumpkin (moschato) with any of the summer squash (pepo) because those two groups will cross-pollinate.

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All this make the price of new seeds look really reasonable.  

What we might consider is recruiting a small group of gardeners to each plant one of the combinations that will work, and then to share fruits and seeds with all the others.