Newly Registered
Posts: 1
Joined: Thu Jan 12, 2017 9:07 am

Soil mixture for raised bed

I am creating a 8' long x 4' wide by 10" high raised bed. What ratio of garden soil, compost and peat moss do I need to start the bed? I debating on what bagged products I should get. It will need 27 cubic feet of soil. I will have 3 beds.

I can get compost delivered but the others I will need to pick up myself. The local nursery has very good bagged garden soil that I bought before when the garden was direct in the ground. I had major problem that developed with Bermuda grass that just took over the beds that I stopped gardening for 3 years.. I do not want to use the existing soil? There is not that much clay in the soil.

If I should replace one or more of the soil components or have any other recommendations you have are welcome. Thanks

Posts: 11684
Joined: Tue Jan 01, 2013 8:32 am
Location: hawaii, zone 12a 587 ft elev.

Re: Soil mixture for raised bed

Welcome to the forum, thursdayrecords. It is a good idea to add your location and zone to your profile so we know the conditions you are gardening in.

If you have time you can save yourself some money if you make a lasagna bed and put 4 inches of potting soil on top if you want to plant sooner. ... 2015_0.pdf

Otherwise Mel's Mix works
one part peat moss
one part vermiculite
one part blended compost from multiple sources. (usually you have to have 5 different types of compost like composted manure, mushroom compost, black cow, black gold, leaf mold, composting facility)

Peat moss (3.8 cu ft) and vermiculite (4 cu ft) can be purchase in bulk bags from an agricultural supplier. Most companies will deliver if you order at least 50 bags of anything in total. Peat moss is compacted so one bag will decompress to twice the volume so one bag of compost will need 2 bags of vermiculite and 2 parts of blended compost.

It can be mixed on a tarp with a shovel or if you are doing a large volume, rent a small cement mixer and mix the components in the mixer. Moisten the mix as you add it in. Peat moss is very hard to wet and you want to avoid dry spots.

If you have a local composting facility, ask if they sell a nursery or garden mix. It usually has the compost, sand, soil, and sometimes manure in it and it is ready to plant. Ask for the soil analysis first to make sure it is not too alkaline.

Mel's mix can get pretty pricey if you are going to fill a lot of beds with it, but you can do sheet mulching on the beds and just make enough Mel's mix for the top 4 inches in order to plant it sooner.

People here have been able to get kitchen waste from local retaurants but you will have to screen out some of the unwanted stuff like plastic wrappers and styrofoam. Coffee grounds and filters are o.k. It is better if you provide them with the containers with tight fitting lids and you pick it up promptly. Let them know when you don't need anymore. For browns you can ask the local tree trimmers for chipped material. Make sure they don't have weeds or use trees like black walnut. You can get a mountain of that delivered usually for free if they are in the area as long as there is good access. Whatever you don't use for the browns you can use as mulch or for the start of your own compost pile. Stables and farms are good places to get manure for the compost pile but fresh manure should not be used in beds you are going to plant right away. They need to be composted or aged at least 120 days before harvest. Manures may contain weed seeds so you want to compost that as well. Compost piles need to be at least 3 ft tall and and longer than 3 ft with the right proportion or greens, browns, and water to heat up well. The more frequently a pile is turned after the first week, the faster compost gets done. The downside is that the organisms are relatively dormant in winter and composting happens very slowly. The activity speeds up once the weather warms. Most people start the compost pile in the fall and let it sit over winter and slowly decompose.
Happy gardening in Hawaii. Gardens are where people grow.

Greener Thumb
Posts: 1030
Joined: Mon Oct 19, 2015 9:12 pm
Location: central Ohio

Re: Soil mixture for raised bed

I would start by putting a thick layer of cardboard or newspaper down on the grass in the areas where you want to build the raised beds. That will kill off the Bermuda grass. Then add your layers for lasagne gardening.

Make sure the beds aren't close to any trees. Tree roots will fill up your beds and suck the moisture right out. Then no amount of watering will keep your plants alive.

You could also try killing your present grass through solarization. You water the area well then spread clear plastic over it. Put soil or boards or bricks/rocks or other material on the edges to hold the plastic down and keep the heat in. When the sun shines on the bed it essentially cooks the plants growing there. But this takes several months and a lot of warm sunny weather. If you don't want to wait that long and are determined to kill the grass you can spray it with grass be gone herbicide. It's not organic and may take 2 applications but it is effective.

Return to “Raised Bed Gardening”