raised bed questions

Sarah80November 16, 2012

I'm looking to perhaps add some raised beds, probably stone or other decorative material, in some parts of my yard.

My concern is cold hardiness in general. Since a raised bed, like a container, has cold exposure on the sides as well as the top, logic would say the root zone of these plants ends up a lot colder in winter than it normally would.

Is there a guideline to this? Or, is there a specific size of a raised bed to where this is no longer an issue?

In other words, if I'm in zone 5b, would a plant JUST hardy to 5b be vulnerable? Should I plant for a zone colder in this case? Is there some rule of thumb here?

Summer heat is also a concern, but could be offset more easily I think with extra irrigation.

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Since no one else is answering, I'll give it a go. It's likely that your thinking about the issue is on the right track but I doubt you'll find definite answers about the questions you've posed. Why? Because there are simply too many variables ... micro-climate, container mass, material thickness & insulation value, soil composition, moisture content, maintenance performed, exposure to sun, etc. I'm sure there are more. Imagine the lengthy, expensive study it would take to make detailed sense of it all. It's likely you'll find various lists of plants that survive cold while in containers, but surely, there's many more questions to be answered about them (and other plants) than there is information committed to the repository. But that's gardening and landscaping! The best thing is to consult some of the various lists pertinent to your area, and commit to doing some experimentation on your own in order to discover what works. Maybe you'll be the scientist that puts it all together in a comprehensive volume. So much work to be done ... so little time.

    Bookmark   November 17, 2012 at 6:56PM
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bahia(SF Bay Area)

It would mostly depend on the type of winter you get. If you tend to get a blanket of snow that will cover and stay, there would likely be little difference. The thickness and material of the raised bed edging would make a difference as well. Thinner wood would expose the soil at the edges to more cold penetration than would bulkier rock, but again, these differences would be muted if both are in any case covered by protective insulating blanket of snow. I'd imagine that in a wide bed 4 or more feet wide, more than 18 inches away from the bed walls, the raised bed wouldn't be any colder than a naturally occurring berm or slope that also presents a raised profile relative to surrounding ground areas. If the soil in the raised bed is different from the native soil below it, as it might likely be if you imported topsoil to create the bed, it may also have colder characteristics than native surrounding soil.

If you don't have an insulating blanket of snow, throwing down a good depth of mulch over such a raised bed would be a good preventative method to equalize the cold extremes and be able to stick with plants minimally hardy for your zone.

    Bookmark   November 18, 2012 at 6:48PM
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hmacflower(Z4 Ont.)

I plant at least 1 zone less (Z4 perannials) along the front of my raised beds, further back doesn't seem to be a problem...for tall walls a hardy vine such as honeysuckle planted at the top to cascade down works well, for shorter walls, creeping phlox, geranium, sedums, sempervivum ,common aguga, but not the newer varieties, campanula carpatica, but not muralis, golden oregano are a few you can try.

    Bookmark   November 26, 2012 at 12:22PM
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