scvirginia said:I usually try to plant things somewhat above the tree roots if I can... Sort of like raised beds without the hardware, if that makes sense.
Tree roots *thrive* in raised beds.
My problem was eucalyptus trees, not because of shade, but for their very aggressive roots. My solution was raised beds with heavy black plastic under them. I think it was 6 mil or 8 mil. I used two layers, with some cardboard above the plastic and some 1/2" galvanized hardware cloth on top of that in case I accidentally dug a little too deep. The cardboard is needed because hardware cloth can have sharp little points on it. It sounds obsessive, but the slightest pinhole will let water through and roots in. Make sure the plastic extends well beyond the sides of the bed so that tree roots can't find their way in. I line the inner surfaces of the "walls" with plastic to keep the soil from rotting the wood. They were a little more trouble to build, but they've been in service for almost 30 years and are still sound.
With a plastic bottom, the beds are essentially large containers. Mine are about 14" tall, and the daylilies grow fantastically. I don't know what's available in your area for "topsoil", but my local yards have a product they call 'sandy loam', which is very sandy soil with some redwood and manure mixed in. It packs pretty quickly. Most bagged mixes are junk, containing large amounts of ground-up waste wood from recycling centers. Absolutely the worst thing you could try to grow plants in; it molds, packs, and supports mycelium overgrowth.
I recommend a mix of 5 parts ground bark (1/4"—5/16" size), one part "topsoil" or potting soil, and one part coarse perlite. A tablespoon of dolomitic lime per gallon of bark should get you started. (If you can, dampen and lime the bark, then let it sit for a week or so before use.) This mix may appear to be too "open" and "light", but it grows *great* daylilies, and doesn't break down into an airless muck after a season like commercial potting soils will. Ideally, this soil mix should be fed with Dyna-Gro Foliage Pro, which provides an ideal NPK profile, as well as trace elements, including calcium.
