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Raised Bed Soils

Last week I talked about the different materials that can be used to construct a raised bed. This week I want to talk about what we put in the raised beds. There are many different options out there, some are better than others are, and some are cheaper than others are. So let’s talk through some options for soil in your raised garden bed.

Before filling up your raised garden bed figure out how many cubic feet of soil you will need. This is a simple calculation of multiplying length by width by height. Let’s use the dimensions 8 feet X 4 feet X 10 inches. In this case, we would multiply 8x4x0.833 because 10 inches is 0.833 feet. The answer is 26.66 cubic feet. If we wanted to convert cubic feet to a cubic yard, we would divide our cubic feet by 27. This means that we have close to one cubic yard of volume.

Now that we have the math out of the way and know how much material we need let’s talk about what materials can be used. Obviously, you can use top soil to fill the raised bed. If you have extra top soil nearby this might make sense for you. Otherwise, I don’t think that it’s a great option. Top soil is not regulated in terms of what is in it. So you might have many chunks of bark that haven’t started decomposing. If you don’t know the source of top soil, it could also contain weed seeds that will grow and compete with your plants.

Another option would be to go to the store and buy bags of soil that are made for raised beds. This would give you quality soil in the beds. The flip side is that you’re going to spend a lot of money doing it. You could easily spend $250 or more for soil using the dimensions I talked about earlier. If the money is not a problem, this is a quick and easy solution.

Compost is a great way to fill your raised beds. Compost that has completely composted will provide many nutrients to the soil. If you have your own compost you can use that, or you can buy compost in bulk. Some companies will deliver or if you have a pickup truck, you can use that. You can also buy compost in bags. A product like Black Kow is an example. Buying bags will be more expensive. One drawback to using compost is that the pH will most likely be high. This can lead to some nutrient shortages. Another thing to keep in mind with compost is that it will continue to decompose. This means that the amount you have will decrease and more will need to be added periodically.

The lasagna method is a popular way to fill raised beds. You alternate layers of brown and green material. Brown material is dry leaves, shredded newspaper, peat, and pine needles. Green materials are vegetable scraps, garden trimmings, and grass clippings. The green materials contain nitrogen and the brown materials contain carbon. Make the brown layers twice as thick as the green layers and it will compost down into a good material into which you can plant.

If you have beds that are very deep another option is the put branches in the bottom to fill up space. The branches will break down over time, giving you good material in which to grow.

If you have questions about filling your raised bed contact your County Extension Office or email me at