Marshall, I think a cross between those two species might be very exciting!
Have you seen pollen cones on your Pinus strobus before? If it doesn't produce seed cones, then maybe it isn't donating pollen, either..

-Sam

Sam - There are usually a few pollen buds opening when I shear and I remember them emitting pollen when disturbed.

Marshall

It's possible that the species have slightly different pollination times, so if you want to maximize your chances of getting a hybrid, you should store the pollen from one species and manually pollinate the other species. You should also ensure that the recipient immature female cone has a "chastity bag" preventing pollen you don't want from touching it. If the prevention works 100%, then you can get an estimate of sexual compatibility between the species by counting number of sterile vs viable seeds, germination rate, etc.

Here is a great video showing how they cross-pollinate Southeastern US pines, subsection australes (loblolly, longleaf, shortleaf, slash, etc). The principle is the same for any conifer:

http://www.youtube.com/watch?v=Sq39gEDDKDs

Here is a link that might be useful: Manual cross-pollination of pines

The cross has already been made, it's called Pinus ÃÂ hunnewellii.

Resin

Edit: add link to pics

Here is a link that might be useful: Pics

This post was edited by pineresin on Mon, Dec 9, 13 at 21:04

Thanks for the replies -- which make me wonder if the p. x hunnewellii is/was a natural occurring cross or a manufactured one using techniques that Bluecone commented on?
Anyway, I dug and potted the seedlings and will have the horticulturist at the arboretum where I volunteer plant them out somewhere in a couple years and we'll see what happens with them.

Marshall

It was a spontaneous hybrid, seedling found at the Hunnewell Arboretum.

Resin

Thanks Resin
So there's a chance
Marshall

Are there any identifiable characteristics of such a cross or is it only possible by seed cones and expert eyes?
I have some Pinus parviflora spread around the garden for more than 20 years and a native Pinus strobus forest next to us. There are many self-sown seedlings appearing everywhere in the garden. Just in case...

A fair chance of it being distinguishable by 3-4 years old; the foliage is intermediate between the two parents.

Resin

Pinus x hunnewellii, it's just a good exemple between the parents,in form, in foliage, in cones. Here the cones photografied in my arboretum.
Clement

Thanks Resin and Clement. I will try to keep some of those seedlings and keep an eye on them. Clement, I hope you don't mind I saved a copy of each of your images for future reference.

There's a few nice specimens of this cross at the Minnesota Landscape Arb. The best are very glaucus, approaching the bluest of Japanese White Pine. I planted a P. parviflora 'Negishi' near a large native White Pine, with this area surrounded by an open woodland. This is perfect for seedlings to pop up and I'm hoping to get lucky. :)

This post was edited by basic on Mon, Dec 16, 13 at 20:24