My family and I would like to build some raised garden beds in our yard and attempt an organic garden this year. We were wondering how large the garden beds could be before we would need to secure them with posts below the frost line – we were hoping to build simple raised garden beds that don’t need to be secured into the ground with posts.
Currently the 3 raised garden bed areas we measured are 4×12, 4×9 and 4×9 feet. Could these sizes be constructed without needing anchoring into the ground? We’re unsure of the freezing temperatures in winter would cause heaving. We are located near Lake Ontario.
Raised garden beds are an excellent way to grow vegetables and flowering plants, for a number of reasons, including: the soil warms faster in spring, the beds are more accessible, the soil doesn’t become compacted by foot traffic, and they are easier to keep free of encroachment from grass or invasive plants.
It sounds as if you’re considering building raised beds using lumber. In that case, they don’t need to be like a permanent construction — they can be simply placed on the ground. They will move a little with the frost, but that might happen even if you tried to secure them underground.
If you want wooden raised beds, cedar is probably the best option. It is rot-resistant and will last longer than most other kinds of lumber. Pressure-treated wood is not recommended for raised beds because of the possibility of chemicals leaching into the soil.
Your dimensions are along the lines suggested by experts — a bed no wider than 4 feet, so you can easily get to the middle of it from either side, and of 8 to 10 feet long. A 12-foot length is also fine, but any longer is more difficult because of the lengths that lumber comes in. The following article explains how to determine the size of beds built from lumber:
Here’s an example of how to build a raised bed:
Besides lumber there are many other building options, including wattle, logs, concrete blocks, even sandbags (see Rodale’s Organic Life, https://www.rodalesorganiclife.com/garden/diy-raised-garden-beds).
Here’s an answer to a similar question:
For information about growing organically, the Toronto Master Gardeners, in partnership with the City of Toronto, have prepared a number of Garden Guides on organic fertilizing and soil improvement:
The basics of organic fertilizers: https://126.96.36.199/~torontom/wp-content/uploads/2012/07/Organic-Fertilizers-Basics.pdf
Improving your soil organically: https://188.8.131.52/~torontom/wp-content/uploads/2012/07/Improving-Your-Soil-Organically.pdf
Which organic fertilizers to use with which plants, including vegetables: https://184.108.40.206/~torontom/wp-content/uploads/2012/07/Organic-Fertilizers-Specific-Plants.pdf
Controlling insects organically: https://220.127.116.11/~torontom/wp-content/uploads/2012/07/Combat-Common-Insect-Pests.pdf
Good luck with your new raised bed garden.