Don't put rocks at the bottom. They should actually do okay in the conditions you describe, but I think your idea to put them on plywood is good, but you should also use plant feet or something to raise the containers off the plywood to allow them to drain freely. For winter use Wilt-Pruf to keep them from dessicating in the winter winds. If you have good snow cover in the winter that's good. If not, check monthly to see if the plants need watering, and water when it's above 40. You may be surprised at how well they'll do.

Good luck. The Thuja is the more hardy of the two. Taxus has very succulent roots & will react very poorly to single digit temps, if you get through the summer - they don't like hot roots, either. I'm thinking it will be necessary to water (in winter) a little more frequently than Posiegirl suggested, but frequent checks for soil moisture should solve that question.

Though you didn't ask for this opinion, Juniperus would surely be a less frustrating plant material for the conditions you will deal with.

Al

Thanks you two! Questions: Why not use some 1" gravel at the bottom of the containers? Also, would juniperous "sky rocket" be a good choice? I will see what our supplier has in stock. The taxus was just a thought as I have been rushed into this. ( For no logical reason. ) Thanks again. Just recently came across this website. What a great resource!

If you want tall & thin, skyrocket would work, but remember, they get tall quickly & will blow over unless in a large, heavy container or unless the container is secured. There are many other varieties of uprights that have a little wider habit, too. After rereading your original post, I'm guessing you need some height? You didn't say. If not - "Gold Coast" or "Old Gold" or any one of a number of varieties of intermediate ht. J. chinensis would also work for you.

Al

Gravel in the bottom raises the water soaked bottom soil layer and gives the roots less room to grow.

1" gravel and Taxus are out! Drainage is now my concern. I am thinking of drilling 5-6 1/2 inch holes in the bottom. The center of the bottom of the containers is raised & the outer ring would be flat on the roof or plywood. So I need to put "feet" on the bottom? ( These containers should come with directions! ) Would they drain without them? Am also considering putting some styrofoam packing "peanuts" on the bottom. Good or bad idea? Sorry to go on & on with this! This will be my last post on this subject! Once again, thanks for the help.

I'm new to the forum but have 200 gallon containers that I have 1/3 full of styrofoam peanuts. Helps keep them from being too heavy in addition to drainage. I am on my third crop of vegetables in these containers and they do very well.

Definitely use the Wiltpruf. I have several outdoor evergreens and it makes a huge difference in how they come through the winter - less winterburn.

Skyrocket juniper is very hardy on my deck but does tip over. What are your containers made out of? Unless they are really heavy (such as concrete) you may want to consider using bricks on the bottom, or even the gravel, not for drainage but for weight.

I have also used Sky pencil holly, Alberta spruce, and andromeda successfully in outdoor containers subject to cold winds. Good luck!

Have you thought about putting some drapey annuals around the evergreens for summer interest? Variegated ivy or Wave petunias work well.