“Dirt Day” is always a fun day over at my house. My preschooler looooves to dig and it’s one of her favorite parts to getting a new bed together.

In the All New Square Foot Gardening book, Mel Bartholomew suggests this formula for making up your soil mix for your raised bed:

• 1/3 vermiculite
• 1/3 peat moss
• 1/3 compost

In a 4 x 4 ft raised bed that is 8 inches high, that translates to about 3.5 cubic feet of each thing.

That doesn’t sound so bad until you go to the store and figure out that compost is sold by the pound, you get peat moss in bales or litres, and then the best vermiculite source I found sells in quarts or bushels. (Hint for homeschoolers: There’s your math lesson of the day — converting things from one volume measure to another!)

Luckily, you don’t have to be exact.

SHOPPING LIST

First, go to the Home Harvest website and order 1.5 bushels of vermiculite. They will ship to your house. Even with the shipping, I haven’t found vermiculite locally in this quantity for a better price than the ~$30 it costs. It is your most expensive soil mix ingredient, but you never have to put it into the bed again. It won’t rot away. (Don’t substitute with perlite — perlite has a habit of rising to the top and floating away in the rain.)

It takes about a week to arrive and when it comes, save the box and packaging.

All the rest I picked up at Lowe’s this afternoon for $40.

• 1 bag of Black Kow compost — 50 lbs
• 1 bag Black Velvet Mushroom Compost — 40 lbs
• 1 bag Timberline Organic Compost (cow) — 40 lbs
• 3 bags Majestic Earth Peat Moss — 44 L per bag

The peat moss doesn’t have to be Majestic Earth Brand — any will do. Try to go with 3 to 5 different types of compost if you can. The more varied, the better, but shoot for three at minimum. But don’t worry if you have to adjust for costs and budget — just go all Black Kow. You will still grow things.

FILLING THE BED

Mel suggests using a tarp to mix all the ingredients together. My helper is too small to deal with trying to fold tarp full of more than 120 lbs of soil mix and I don’t feel like washing the tarp afterward so we do it this way instead… sort of lasagna gardening style but not quite.

The first step is to put down cardboard at the bottom of the bed. If you saved your vermiculite shipping box, you can use that. If not, use a thick layer of paper grocery bags, newspaper, or a mix of all three. This will kill off the grass and prevent weeds from popping up into your bed. If it is flying around, wet it down with a hose so it stays put.

Next, dump two bags of peat moss in. Use a rake to spread it around to cover the cardboard.

After that, dump in the two 40 lb bags of compost. Spread it evenly over the peat first, then start raking it so it is mixing together.

Now dump the vermiculite in. Have child stand back because it tends to be dusty coming out of the bag. Wet it down a little bit with the hose if you need to so the dust isn’t flying around. (If dust sensitive, wear a mask or bandana around your nose while doing this.)

Do the same thing as before — use the rake to spread the vermiculite evenly across the raised bed first and then start to mix it into the other ingredients.

Now add your last bag of peat and your last bag of compost. Spread it out evenly, and then mix. Children tend to like the mixing so let them go at it as long as they want to. Just remind them to keep the soil mix inside the raised bed. You will end up with something like this:

You may also end up with a planted rake or two!

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