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Environment
Every other Friday, the Outside/In team answers a listener question about the natural world. Got a question of your own? The Outside/In team is here to answer your questions. Call 844-GO-OTTER to leave us a message.

Outside/Inbox: What's the best filling for a raised garden bed?

A photo of a raised garden bed surrounded by grass and a path. A shed sits in the background.
Lori L. Stalteri "Raised Garden Bed" (CC by 2.0)
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https://bit.ly/3O5GM9o

Every other Friday on Morning Edition, the Outside/In team answers a question from a listener about the natural world.

This week, Kevin asked us on Instagram: “What is the best filling for a raised garden bed?”

Outside/In[box]  Header 2

There are a few different types of raised garden beds, but I think the type most familiar to home gardeners are the ones that look like sandboxes filled with flowers and vegetables.

If you’re an aspiring green thumb, and you haven’t tried it, you should know there are a ton of benefits to planting in raised beds. You can get more food and flowers from less space, you can plant earlier because raised beds drain water better than the alternative, and they’re easier on the back.

But maybe the biggest benefit to a raised bed is that you can control what soil and other fillings you put in there, customizing each plot to the specific plants you’re growing there.

To get some tips on what to use for filling, we reached out to Yolanda Burrell: Founder of Pollinate Farm, an urban farm in Oakland, California, where she grows mixed vegetables and cut flowers.

And her answer? Well, it’s classic Outside/Inbox material: “It depends.”

“It depends on where you are,” Yolanda said. “It depends on your budget, it depends on your climate.”

So where should we start then?

Well, the first and most important ingredient you’ll need for a raised bed is soil. If you want to buy it, most of the bags you buy at your local hardware store or garden center will tell you broadly what they’re designed for.

Ideally, you’ll want to mix that soil with compost or well-decomposed manure (or both) and something to help keep the filling loose and well-drained. That could be vermiculite, coconut fiber, or even just sand.

Sadly, there is no magic formula (as far as we know) but you’ll find plenty of raised bed filling recipes online. One breakdown we’ve seen is 40% soil, 40% compost, and 20% vermiculite.

Of course, you’ll still need to know how much to buy. Luckily, there’s a handy soil calculator that can help you figure out exactly how much you need, depending on the size of your bed.

More advanced gardeners might want to make their own soil, rather than buy it from the store.

“Get yourself a big wheelbarrow,” Yolanda says, “ some local topsoil that hasn't come from a construction site or something like that. You can then add your own amendments, you can add your own compost or your own steer manure or rock phosphate, rock dust, any kind of minerals that you want. Mix it all up real well. It'll give you a nice, crumbly, dark soil.”

One more thing that may impact your choice of filling is bed height. Different plants need different soil depths: Herbs and flowers need only about 6 to 12 inches, whereas carrots or beets need deep soil. So depending on what you’re planting, you may be able to fill the bottom of a tall bed with sticks, or yard waste.

“You fill the bottom six inches with that and then put the soil on top of it… and you're basically composting in place,” Yolanda said.

Speaking of composting in place, there is a traditional method of building raised beds where instead of having the wood on the outside, you put it on the inside instead.

This centuries-old method is called Hügelkultur, a German word meaning “mound culture.”

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Jon Roberts (CC BY 2.0) https://bit.ly/3vjJijR
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A partially complete hügelkultur garden bed.

First, you pile up old rotten logs, then add layers of yard waste, sand or rock, compost, and soil.

What you wind up with is a long raised lump that feeds the soil nutrients as the rotten logs decompose.

Turning old yard waste into a fresh garden salad? Sounds like a good deal to me.

If you’d like to submit a question to the Outside/In team, you can record it as a voice memo on your smartphone and send it to outsidein@nhpr.org , or call the hotline, 1-844-GO-OTTER.

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