1.)Much debated, actually. It depends on your zone and whether you are planting a bare root, balled & burlapped, or potted tree. As an amateur in Zone 6, I find I have my highest success rate planting potted trees in the Fall. Bare root almost have to be planted in the Spring. The one thing everyone agrees is NEVER plant in summer. And in your zone, when we say "Spring" we mean early Spring. May is too late to be optimal.

2.) Google the species. Some seeds evolved to only germinate after winter, or passing through an animal's guts. They may need to be refrigerated or dunked in acid or something. Place them in "seed starter" potting soil or those little disks that rehydrate in water. I find I have a higher success rate with larger seeds.

3.) Lots of trees don't mind clay soil. Look for trees that tolerate wetlands and plant them small and young. Magnolia should be a good choice. Have you considered pecan or baldycyrpress?

"When is the best time to plant a tree in the ground?"

See section 1 in this link: Planting a Tree or Shrub

"Can one of you recommend to me a resource that tells me in plain English how to grow trees from seeds?"

I'm not sure exactly what you are looking for. Are you wanting information on germinating the seeds or on routine maintenance or what? If you are wanting germination advice, try googling 'Cornus controversa germination' (without the quotation marks), and you'll get plenty of info. You can also go directly to germination reference sites found at the bottom of this link: Other Resources

"...my yard has approximately 2-4" of soil over dense clay."

Many trees will do well in clay IF drainage is decent (and some clay areas do drain fairly well). How is your yard's drainage? Do you end up with a lake when it rains? How does grass do in your yard (if you have a lawn)? This will give us an idea of what you are working with.

3). My clay is so dense, I can chew it like gum.

My clay is so dense, I've taken up pottery.

I grow two small ginkgos with no issues and a neighbor has a 60 footer in quite clayey soil. Have you considered trying Taxodium since its the baton in Baton Rouge? How long does your soil stay wet? Do you check the soil to see if watering is needed? Have you amended any large areas with compost? I guess more details on your growing practices would be needed to see if anything needs correcting.

tj

Perhaps we need to know how you plant your trees. Please tell us in detail.

Fall is the optimum time for the planting of trees and shrubs in your location. Then winter, and very early spring. I've done numerous installation projects in the summer, too, but extra care must be taken. I spent many years in coastal zone 8b, in South Carolina.

Landscapers do not stop their planting projects in the heat, believe me.

I have very heavy clay, too. Everything grows very well, including our ginkgo, but the clay drains well and is oxygen rich. I never amend the soil when planting and you shouldn't, either.

What color is the clay?

Panoply, do you have a source for cornus controversa seeds of known viability?

Seed of Cornus controversa should be sown as fresh as possible. It needs a warm stratification period of approximately 3 months followed by a 3 months cold stratification period. If you sow the seeds in July (like sam_md above) they will germinate next spring. If you sow them in lets say December they germinate more than 16 months later. Don't know if you stratify the seeds in an artificial way (putting seeds in a ziplock bag with a slightly moist medium for 3 months inside the house and then for 3 months in the fridge) will give good results. I tried the artificial stratification method with Cornus officinalis, which has similar germination requirements, but it did not work.

My results with sowing Cornus controversa have been poor. I probably got 'old' seed that was dried out too much and therefore lost viability.

I've gotten a number of, admittedly small, C. controversa seedlings from musserforests last spring. All have survived so far.