First stuff leaching out will go down. Very little will reach out. Yes roots will hit it. If you are really worried slide some metal down - get white metal coil (used when siding to cover posts, facia etc.). Cheap and slide it down. Now roots must go down to get "under" timbers and for sure all chemicals coming off will not go near 99% of roots. Also in a couple years 75% of chemicals or more will likely be gone. I worry a lot but I think you are ok. I used regular wood - untreated. I bought sealer that was nontoxic. Its not working. Been 3 or 4 years and it is not going to be long before some boards break. I now slope soil down at wood to allow less dirt to touch the boards to let them dry in hopes to make them last longer. PT wood would have been thousands (I made BIG beds)

Hi John 1931, I am a quilter too, so laying out blocks is a nice puzzle. A picture is worth a thousand words, But here's a try. Maybe some index cards or dominoes, Lego bricks, etc would be helpful to fidget with (I used index cards). Lay out a square pattern to show the corners of the first tier, with the blocks making a kind of circle, like this. N N N D B O O D B O O D B H H H (3 letters make a block, the O's are just dirt.) If you now flip that layer over D N N N D O O B D O O B K K K B it will sit on top of the first layer perfectly, and stagger all the joints. Of course you can stretch the sides by adding blocks, but with this corner pattern reversed for each layer, you should need no partial blocks and the joints would always stagger. Just avoid the symmetrical layout: N N N H O H H O H H O H N N N That gets you in trouble on the next tier. Hope this made sense!

It might help to read Eliot Coleman's books on season extending techniques. I have a high tunnel (plastic covered/wood frame) and it is amazing how warm it gets during the day when the sun is out. What I have learned is the soil inside doesn't freeze even though outside it might be zero degrees and it gets zero degrees inside at night. From the list that another poster provided, those are cold hardy plants that can take some cold temperature extremes. Local farmers start using supplemental heat when they want an early tomato crop but they don't try to grow tomatoes all year. You also need to understand that during the darkest winter days, plants aren't getting enough sunlight so they tend to stop growing. Eliot calls this the Persephone Period. Depending on what you are trying to grow you might need both heat and light. (New local hydroponic greenhouses are using a lot of light.) Local market gardeners provide extra cold protection for their plants by using Agribon. I managed to keep rosemary alive for two winters here in zone 5 NH by swaddling the plant with Agribon, removing it in the spring. By providing enough cold protection you can probably grow spinach in the winter but not lettuce. I have had lettuce roots survive and start growing in the spring. Kale, coriander, and claytonia might die but seed and/or roots survive to start growing in the spring. Keep in mind that even snow provides some insulation. Johnny's Seeds website might also have some helpful information about when to sow plants for fall/winter and when to sow in the spring for earliest crops.

A few thoughts from my own experience gardening on a slope. Made a traditional raised bed on a slope - meaning the top edge of the 2' deep bed ran parallel to the sloped ground, meaning the bed was also sloped. With each rain or watering, soil eroded downhill, leaving the top of the bed bare and the bottom with soil overflowing the bed wall. It was a constant PITA to keep hauling displaced soil back uphill. Lots of plants didn't thrive (roots constantly getting exposed, etc.) or outright failed. I work FT and don't have time to toil in the yard everyday so this was an exhausting garden. I suppose the severity of this issue will depend on your slope grade and how much soil runs downhill. Next year, did several containers (in the same spot, right on top of the bed), mostly at the top of the slope with some in-ground plants towards the bottom. Low growing (squash, etc.) were fine but tall ones like tomatoes and peppers ended up constantly tipping over, towards downhill, due to the containers getting top heavy and leaning on a slope. This happened even with large, wide bottom containers. Once the plants got tall, even a slight thunderstorm wind would blow the containers over since they were already leaning downhill. Shimming them with paving stones helped some, to make them sit more level. Third year, built the raised bed wall taller and taller as it went downhill, so the bottom of the slope was tall enough that when filled with soil, the top of the bed was level. (Think: retaining wall on a slope where the height of the wall differs along the hill so the ground remains flat on top.) This solved the downhill erosion issue but the whole experience was tons more work than anticipated. I'm no engineer - I had zero forethought about how things would work on a slope. What if, you made mini-tiers throughout the beds, to accommodate for the gradation of the slope? I grew up in a home with a steep sloped yard and it was tiered (with simple cinderblocks) so each tier had a flat surface. We combined veggies, herbs, cutting flowers, roses, annuals, perennials, evergreens in each area. Each tier had a mixture of plants year round instead of a dedicated "veggie bed." To this day, my veggies are tucked in-ground and in containers all throughout the yard. There is no dedicated vegetable garden or flower garden. And there are very few straight edges - I just let the plants curve here and there organically. BTW, love the curved path for the aesthetics! Sorry so long-winded. Good luck!