In yesterday’s post on garden experiments, Shane Arthur Swing commented on a possible watermelon pumpkin cross he may have created.

I asked if he’d let me know how it happened and share a photo. He graciously agreed to share more details and sent me both a picture and a write-up on his suspected watermelon pumpkin hybrid.

A Watermelon Pumpkin Cross?

Shane Arthur Swing’s story:

I’ve been gardening in Maryland for about six years now.  The first few years were experimentation and learning new plants to grow and new methods to try.

So, about four years ago, I didn’t know any better not to try and cross-pollinate some pumpkins and watermelons I was growing next to each other in separate raised beds. I’d rub the male flowers on the female flowers of both onto each other.

So, the result is visible in the picture – pumpkin-watermelon Frankensteins.

These perfectly ordinary children are completely unaware of the taxonomical abominations that might be unleashed if these watermelon pumpkins were allowed to spread.

Not until this year did I read that doing so was impossible since they aren’t in the same family — I had to dig up the picture from an older computer I knew I had the picture on.

I’d like someone to tell me how in the heck this happened. When I opened up these things, the flesh was more orange-ish than red and had the fibrous texture that pumpkin flesh had but was a bit softer. It was sweet tasting, but not as sweet as regular watermelon if I remember correctly.

I didn’t save any seeds because, back then, I didn’t know this was impossible, and I’d rather just grow individual plants, not mixes.

Is this Possible?

My Verdict

Some strange things have happened via cross-species hybridization and I really want to believe in a jump like this.

That said, upon further consideration of this strange case, my understanding of plant breeding leads me to think it’s impossible for the genes to have obviously effected the look of the pumpkins the first year.

Why is that?

A pumpkin x watermelon would not become evident until the seeds were planted, since the ovary (the fruit) is a product of the mother plant. The plant donating pollen would give its genetics to the seeds and if they were planted and the cross took, you could have plants that bore fruit with attributes of both parents the next season – but this would not be evident until then.

The fruit is a genetic outgrowth of only one parent – and it isn’t the pollen donor. The embryos within the seeds of a pollinated fruit, however, contain traits from both parents.

If you cross-pollinated watermelon and pumpkin and were able to get a successful hybridization, you wouldn’t know it until you planted the seeds the next year.

The best way to tell if you successfully pollinated a bloom – without waiting until the next year’s fruits – would be to do what squash breeders do and tape or tie the female blooms shut the day before they open for the first time. The next morning, you open the blooms and pollinate them just with your male donor flower, then close them again. This ensures that an insect doesn’t sneak in and pollinate the flower when you’re not around.

If the pollination “takes,” the flower will fall and the fruit at its base will grow into maturity. If it doesn’t, the nascent fruit will simply fall off in a few days.

Now – as for whether or not you can hybridize a pumpkin (Cucurbita pepo, C. maxima or C. moschata) and a watermelon (Citrullus lanatus), it is rarely possible to make these types of crosses.

That doesn’t mean it can’t happen. Just that it hasn’t happened and been recorded. Home gardeners are responsible for most of the variety in garden vegetables and fruit we have today, and they’re even responsible for some new species.

Sometimes a cross will happen but all the seeds will be infertile.

Watermelons and pumpkins share the same family Curcurbitaceae but they aren’t all that closely related and they don’t reside in the same genus.

Cross-genus hybrids aren’t impossible, though. Triticale is a cross-genus hybridization between rye and wheat.

Stabilizing a cross of this nature usually takes some work once done, however, as there are plenty of strange things that happen when chromosome counts, etc., get mixed together.

So What Happened With Shane Arthur Swing’s Pumpkins?

Whatever created this abnormal manifestation in these pumpkins must have happened due to a cross in the previous generation or a mutation.

Plant mutations have led to many of our most beloved fruits, flowers and vegetables.

Consider the story of the Navel orange, for instance. One mutation two hundred years ago created one of the most popular oranges in history.

One mutation that led to one branch was later cloned into millions of trees. Photo credit Forest and Kim Starr.

A Presbyterian missionary came across the Navel orange back in 1820 and saved it for posterity. Without him, that branch would be long gone and I wouldn’t be enjoying one of my favorite fruits.

Oranges aside, pushing for crosses and saving mutations is a lot of fun. These pumpkins were likely crossed with another type before Shane planted the first seed in his garden that year – but by all means, keep attempting strange crosses.

If you want to end up with a stable line and your own varieties, I highly recommend Carol Deppe’s book Breed Your Own Vegetable Varieties. It’s fascinating and contains lots of information, including some of her own thoughts on “wide crosses.”

Keep on experimenting. A watermelon pumpkin cross may yet happen.