Cheap Way To Fill Raised Beds

David Trammel's picture

There are many challenges to gardening in a urban area, but there are also advantages. One of them is that people conveniently bag up the organic waste you need to compost or to make a raised bed. For the last few months on Tuesday I drive around and grab a few bags of filler. I have a lot of raised beds going in, and if I had to buy dirt, I'd be out big bucks.

Here's a way to save money AND to give your Future plants a bountiful place to grow. Hügelkultur enthusiasts will recognize the method.
Picture #1: I'm using metal raised beds on top of concrete blocks, which are inset into the ground. In this case I'm doing two 2x8' and one 3x8' bed, set against a vinyl privacy fence of my neighbor's. The beds are being set up in a U shape, in the corner of the yard.

The 2x8' ones are small but I didn't want to have to reach across them to weed, since the other side is inaccessible. Because of this and because I had to use full size 8" concrete blocks against the vinyl fence side, the interior area is smaller than normal. All the other beds use a half block (4x8x16") for the support. You can see the blocks in this picture. Because the back side of the brick is beyond the wall of the raised bed, I decided to cover them with a piece of 1/2" hardware cloth as well as also cover the bottom with a similar piece to protect from pests.

First step is to cut up limbs and sticks, then fill the lower third of the bed. I didn't go above about 2" thick, given the smaller size but in a bigger bed you could put larger ones.

Picture #2: Once you have the amount you want, add either some fill dirt or some compost. My side neighbor bought a truck load of compost, too much for what he needed, so he said I could use some too.

You don't really need to do that, the organic leaves and stuff you are going to add on top will settle as it degrades, but adding it gives the earthworms a pathway to move around the bed.

Picture #3: Now you just add leaves. I filled this all the way to the top.

In a few other beds I also added a thin layer of grass clippings. I get them from the neighbor across the street since he warns me if he is going to use any herbicide. He hasn't this year, so I'm sure the grass is safe. Unfortunately we had a big storm a week back, and he hasn't mowed. I did get all this from the neighbor with the compost, from a tree that came down in his back yard.

Unknown herbicide in your straw mulch can really hurt your plants and force you to dig out your beds completely. The secret with grass clippings is to layer them in on the top, do it in a thin layer, and importantly, let them sit for a day or two to brown up some and lose moisture first.

Picture #4: I tossed a wheel barrel's worth of compost on top of the leaves to compress them down, then gave the bed a good watering.

Picture #5: I have several other beds which are further along the composting down path. This one here gives you an idea of what you get after a few months, though I should have watered it before I took the picture. It's a deep black when its moist.

As it was decomposing, I would give it a forking over and some water once a week. I was getting some huge worms in the mix. I turned four beds over today, and removed a dozen worms from each, seeding them into the new beds.

Final thoughts: This is fairly easy to do, though you have to be in it for the long haul and be consistent about turning the beds. You are in effect, creating miniature compost piles. But the ingredients are free and will give you a great start.

How does this help? First, decomposing organic material is a great nutritional source for plants. All those minerals and carbon gets broken down by microbes and earthworms, and the roots suck it right up. It also helps keep the soil moist. As wood decomposes, small empty spaced develop. When it rains or you water the bed, moisture is absorbed and stored in the wood, then is slowly released.

I'm going to continue to build and fill the beds I've got planned thru the Fall. I may plant some Winter bulbs and seeds but the majority of the new plants will go in the ground in the early Spring.

You may want to pave the space between the "U" with salvaged bricks or pavers (yes, sometimes people discard perfectly good stacks of bricks. You may have to chip off the mortar, but it's doable.)

The reason I suggest this is mud.

You'll get so much foot traffic from working on the beds, kneeling and weeding and so forth, that you won't get grass to grow easily. You'll also need a string trimmer to keep up with the edges unless you don't mind weeds creeping in and out. If you get bindweed, it will grow from the bottommost cracks.

Having tried mulch (muddy, weedy mess); grass (muddy, weedy mess), gravel (harsh under foot weedy mess), sand (muddy, weedy mess), bricks (weedy but dry) and pavers (larger spaces between the weeds and dry), I suggest the hard surface.

Because they're smaller, bricks fit better into odd-sized areas. They can be turned on their side or on end to fit better. You will get weeds in the joints but it won't be muddy. The cheapest bricks (if you don't get lucky and have someone demolish a house nearby) are concrete bricks at big box hardware stores. They're gray and about 50 cents each. Much less expensive than real brick. Light colored bricks also reflect sunlight up, which can be useful in marginal sunny areas.

The joints will let bricks or pavers dry quickly; water will seep between them.

The other nice thing bricks and pavers do is act as a heat sink in the winter, warming the beds sooner in the spring and letting them stay a hair warmer in the fall. I haven't noticed a problem with too much heat in the summer from the bricks.

David Trammel's picture

I do have a pretty good size pile of 12x12" pavers I planned on putting down in the high traffic areas. I want to bring the ground level up some in that corner, probably to within 4" of the top of the top concrete blocks. There's a significant dip back there, but it doesn't seem to have drainage problems. Once I get the height I want, I had planned to lay some sod, but I'm not sure if later in the Fall would be a good time to do it. Might have to wait til Spring.

ClareBroommaker's picture

Do you find your fork gets caught on the branches when you turn the composting material?
Are worms bringing some actual soil up into the mix in picture number five?
Does your town or city make available free or low cost compost?

David Trammel's picture

1) In the first bed I did (not these), I mixed the sticks and the composting material thru the medium. Big mistake. The forks did in fact get caught on the branches. After that, I put all the branches in the lower 4-6" then organic material in the rest of the space. When I fork those, I don't go as deep with the fork. If I feel resistance, I pull the fork out a little and try again. Mostly I'm forking the mix to provide air into the center for the composting microbes.

2) I'm not sure. I know that the worms are often in the middle of a clump of clay. The mix is broken up pretty well though. The only clumps that get into it are when I toss some of the dug up dirt from when I put in the concrete blocks. I know they are fat and plump, nearly thick pencil size and fast too. You have to move or they get their nose into a crack and are gone.

I've been surprised how quickly the leaves, grass clippings and other non stick organics have composted into the rich loom in #5. I expected it to still be in layers.

In about late October I'm going to try and prep for the concrete pad by digging up the area where it goes. I figure I'll have about 3-4 inches of top soil to add on top of the composting stuff. I'm going to seed clover as a cover crop for the Winter, then turn it back into the soil in the Spring before I plant.

3) My city does offer free compost, I've not checked into getting any. I wasn't planning to use any but like I said the next door neighbor put some flower beds in and over bought a truck load of compost. He's still got half the load on his driveway so he was happy to share if I can cart some off.

Beware of free compost from unknown sources. Aside from pesticide residues you could bring in diseases like club root and the fungus that kills garlic and onions.

I built a new raised bed this year in the yard of the house we are renovating next door. Filling it with soil would have been rather expensive, but I did buy one load of soil compost mix. It wouldn't have filled the bed, so my garden buddy suggested we fill the lower half of the bed with some bails of very weathered straw. Worked fine and we spread the soil several inches thick over the straw and planted peas.

This is where it get interesting. The peas came up and it all looked good, but the didn't grow as well as the peas next door that were planted some months earlier. Now, granted it got real hot real early this year, but they looked to me like they didn't have enough nitrogen. That seemed a bit weird since they fix nitrogen, but they did look somewhat yellow. A little later on a friend brought over a garden book that showed a similar layering method and the author said he put down some blood meal or something like that before he put the soil, compost mix over the straw.

Well, that could have been what effected the peas, but the corn we followed the peas with doesn't seem to be showing the same yellowing problem. The corn should be using the nitrogen the peas put down. So, could it have been that the straw sucked up all the available nitrogen that the peas would have used as it decomposed as some garden books say high carbon mulch can do or was there some long lasting herbicide in the straw that stunted the peas or was it just the heat? I don't really know, but I think you would do well to mix in more green grass clippings for the nitrogen they bring or maybe some fish emulsion. Maybe we were just in too big a hurry and didn't prepare the bed properly.

Here's my compost story. I had a box with leaf mould maybe two years old. Looked pretty nice so I planted spuds in there. Well, they came up nicely then turned very yellow. Classic case of lack of nitrogen. So I pulled out my jar of triple 20 soluble fertilizer, gave them one watering of it and they were fine in a couple of weeks and never looked back. So in later reading about the life of compost, it has been observed that it goes through different phases over time. It starts out with a bacterial decomposition then hopefully ends up with a fungal population. At some point it stabilizes so that you need not worry about the nitrogen being leeched out by rain. After declaring bad things about leaf mould, those darned spuds came up again the next year (you can NEVER dig them all out!) and lo and behold, no yellowing, just really nice looking plants. Live and learn!

bobmcc's picture

From what I've read, legumes don't provide the nitrogen-fixing bacteria necessary to fix nitrogen - they use the nitrogen-fixing bacteria normally available in the soil. It's my understanding that not all soil contains nitrogen-fixing bacteria but nitrogen-fixing bacteria are available in bottles in most nurseries.

Thanks. I had forgotten that. That could well be the reason that my peas were yellowing. I needed to use an inoculation. I remember reading that too some where, but of course I had forgotten all about when it came time to plant.

Sweet Tatorman's picture

If the lack of the correct bacteria is in fact the problem, rather than buying inoculant, you can inoculate with soil taken from an area that you have previously successfully grown a similar type of peas. Different legumes have different compatible bacteria.

That sounds like a good idea. I have use inoculant in the older garden beds in the past and since peas and beans seemed to be growing in those beds just fine, I stopped using it. I will try transferring some of the soil from the older beds to the new one. It might be the right thing to do for any new bed.

Thrifty1's picture

I'm trying to run my allotment on No-dig principles, though it's an uphill battle as I'm on the edge of the site, next to a hedge & ditch, then a field, so there are always nettles, brambles and all sorts of unwanted guests clambering over the fence and dropping their seeds into my vegetable beds, aided by the resident birds. (Who also eat caterpillars, flea-beetles & lots of other pests, so not totally begrudged!) But I've been helped greatly in the last couple of months by a friend giving me the grass clippings from her large lawn, which is never treated with any chemicals. The idea is, never leave a bed empty; always have something ready to pop in as soon as the last crop has been removed, then mulch heavily with the grass clippings. This is the first year I've tried this, and I can report that I've had my best-ever potato crop, and the ground I'm pulling them out of is superb; the underlying soil is heavy, compacted clay, which bakes solid after a week without rain, but the beds that have been mulched with the grass clippings are light, keep moisture well, and the weed infestations have been minimal as the seeds haven't had any light to germinate. I'll keep this up for as long as she's happy to give her clippings away!

The other mulch I use is wool, straight off the sheep's back. Slugs - a big problem on the clay - hate it, and a woolly collar allows my seedlings to get a good start, rather than be eaten before they can get up & away. It also keeps moisture in the ground, and eventually rots down into the soil, adding nitrogen. Our farmers struggle to sell coloured fleeces, so often give them away rather than burn them. Probably not much use to those of you living in the cities or places too hot for sheep, but if you can get your hands on some, try it!

I have also experimented with wool as a mulch. A friend of mine ran a small wool processing plant and there was a lot of wool, of short fibers that would collect under the very large drum carder. She would gather it up and give it away and I took several bags to put in our community garden plots. It was a mixed success. When we could keep it from blowing away, it was a pretty good mulch in the beds and would break down and that was great, but it was very slow. We tried it as a rather more successful weed barrier in a wider path we were responsible for with much better luck. We tied it down with bird netting and as it compacted and felted, it became a very good weed barrier.