Experienced Gardeners requested to answer this dilemma.
30 inch raised gardening beds to be built at a retirement center are not expensive to build, but the cost of filling all 30 inches of the beds with dirt is making this charitable project seem impossible.
We currently are proposing 5 beds, sized 4 feet x 8 feet x 30 inches tall. We calculate needing 360 cubic feet of dirt to fill all five beds (to within 3 inches of the top). Can we “cheat” to reduce cost by putting free mulch at the bottom of each bed? If so, how much actual dirt do we need to place in each 30 inch tall bed?
We are considering reducing the number of beds we build due to cost of dirt.
I went through this with an elevated raised bed… First, the initial cost is somewhat balanced by only needing to mix in a few inches of compost the next years. This is for flowers or vegetables? I’ve mixed peat (cheap) with garden soil, up to about a third, mixed well, and done ok. But “mulch” is usually recommended only for a top layer, to hold moisture from evaporating and stem weeds. Mixed in, as it breaks down, I’ve read it can rob nitrogen.
Do the boxes need to be 30"? And there are many annuals that tolerate poor soil/regular soil, don’t need “garden” soil. Good luck.
What exactly is the mulch in “free mulch”? If it is chipped wood or dry leaves, do not put it there without composting it first - it will suck the nitrogen out of the dirt.
30 inches seems a lot. My beds are half that height, and things grow in them just fine. That said, filling half of your raised bed with wood chips will make your plants miserable for the reason I mentioned above. I would put crushed rock or something like that for drainage (again, not cheap) or make the beds shorter, but you probably want them tall so the seniors do not have to bend too much… Dilemma.
Sometimes you can find someone who wants “clean fill” removed and will let you take it for free. You could reduce how much topsoil you need with that. Also, you could get people to haul the top fill and save delivery charges, even though it would take more time. How much are you looking to spend? 14 cu yards is not all that much.
Sometimes you can get free clean fill dirt if someone is doing an excavation in the area. The top foot or so should be good garden material. We bit the bullet and did ours with garden mix, should be about $25/yard delivered depending on where you live. We mix in new peat and compost each spring.
If you mix green clippings (grass) and dry matter (fall leaves), you will avoid the nitrogen suck issue.
[quote]
Option 3: The Lasagna Method:
Are you building extra-tall raised beds? Do you live near deciduous trees or have a good-sized lawn? Waist-high beds can be wonderful to garden, but filling the entire bed with good soil is very pricey. Leaves and grass clippings are great bulk organic materials which can be layered into the lower regions of tall raised beds, where they will slowly compost over time into rich soil. Aim for two parts shredded leaves to one part grass clippings. Add grass clippings in thin layers to prevent matting. Straw (not hay, which contains seeds), wood chips, or shredded bark could be included as well. Once the beds are full to within 6-12 inches of the top, add a compostable barrier such as untreated cardboard (it prevents your good soil from sifting down too quickly) and then fill the remainder with your chosen soil mix. Next year, you will find the soil level has sunk due to the decomposition and settling of the lower layers, so you will have plenty of room to add a fresh layer of compost on top! Eventually, the lower layers can be turned over and used as a soil amendment. If working with extra-deep containers instead of raised beds, you can add an inert “filler” to the bottom of the container, such as bricks, milk jugs, or stones. Cover the filler with landscape fabric, which will enable drainage but prevent soil loss, before adding your chosen soil mix.
I would try to get a few garden centers in the area of the retirement home to donate it. Maybe talk to the company that does lawn maintenance for the retirement home - they might be inclined to help.
Okay, I think we have the beginning of a possible solution. The retirement center wants the beds to be 30 inches tall, so we can now ask some questions about how to go about filling the beds up.
How many inches on the bottom can be filled up with some kind of inert material? I am hoping that gathering inert material will be less costly, so am thinking could we go 12 to 15 inches from the bottom all being inert material?
How many inches on the top should be a good grade of soil? We will leave 3 inches of space from the top of the soil to the top height of the bed.
What kind of soil are we looking to purchase/get donated? Is there a name I ask for when talking about good gardening soil? Please speak to me as if I have never put my hands into the ground before, as I do not garden at all.
Any other thoughts as we push this project forward? Any obvious things we are missing?
But using them for veggies changes things, you.may not avoid the expense. After all, you want the seniors to have the satisfaction of seeing some produce. Ugh.
You want a rich blend. Look at Square Foot Gardening, the Mel’s Mix recipe. I’m only getting better production this year cuz I seriously upped the compost, good stuff partly from the landfill. Maybe they would donate.
You will need a foot of good soil for most of your garden veggies. The soil to fill garden beds is called topsoil or 5-way mix in my neck of the woods. YMMV.
How are the beds going to get watered? Is there a water source nearby so the seniors do not have to carry buckets and watering cans too far? Does the spot for the beds get adequate morning sun?
Btw, real Square Foot Gardening doesn’t need a 30" depth. 12 would be plenty. Since you want the height, can you build these so the planting box is, say, 4 x 8 x 12, but sits on something elevated that you build? More or less, the same cost for materials, but far less soil. If you look at plans for planter boxes, you may see this. The height isn’t all planting area.
Does it have to be 4 x 8? Is this a real lust for gardening or a side diversion?
Where else can you get gardening advice in the middle of the night?? Thanks so much! I think I am relieved enough to head off to bed. Night owls with a love of gardening, just keep on typing and I’ll read all your great advice in the morning.
I have raised beds at a community garden and had the same problem filling them. I basically turned them into compost piles first. I picked up food scraps for a place that made ice cream and also from a coffee shop.
Giant bins of cantaloupe skin, juiced oranges, pineapple crowns, all thrown in. Five gallon buckets of coffee grinds, about 4-6 a week, all thrown in. I kept a bag of mulch or topsoil nearby to make sure I could cover any fruit scraps so it wouldn’t attract flies. I did this for a couple of months before I started added topsoil, vermiculite, perlite, and gypsum.
Since this is a retirement home, a lot of the scraps could come from their kitchen. All uncooked fruit and veg scraps, any plain bread they throw out, egg shells and coffee grinds. The kitchen staff could throw things into 5 gallon buckets as they do food prep and they can be emptied at the end of the day.
You could also use grass clippings, but not from grass that has been sprayed or treated with anything. No golf course grass. And I would be wary of “free fill dirt”. It is usually subsoil and things don’t grow well in it. Your eventual tomatoes will have very deep roots!
Starting it off as compost takes a bit longer but you will have the richest soil imaginable.
My MIL’s assisted living facility has the raised garden beds. They are elevated as in post #13. So essentially a box
on legs. No need for so much fill dirt.
Packer, mine is on legs with heavy duty wheels, so I can move it as the sun moves over the summer. But it’s 2 x 4 and so heavy, when filled, that it’s not so easy to move. The other thing about elevated is the water can drain through and the air circulation dries it out faster. So it helps to have some fine garden mesh at the bottom, to slow water loss. I have vermiculite in mine, but still.
@powercropper isn’t it late to be planting veggies? Or are you somewhere with a long growing season?
Having had raised beds for veggies, I’d suggest at least 24" of soil - my Tomatoes put out roots closer to 4 feet in depth assuming you water deeply - and think about how long a carrot is as an example of a root veggie. I’m not a big fan of the idea of inert material… it will find its way into the growing zone and then you will have to deal with it.
I like the suggestion up thread of starting with a compost pile. Chop up the items going into the beds into small pieces and they will decompose more quickly. Layer in 3 inches of composting material, an inch of top soil… keep somewhat moist. Once you have a full bed, move to the next bed. I’d estimate 2-3 months for rich soil…
I use raised beds on the square foot model, and they are 12" deep, and I use them for roses and others for vegetables, and it works fine. With your 30" boxes, you can use inert material (like gravel and sand), then have the top foot be soil, which would save you a lot of effort and money. Someone mentioned the fill from construction sites, if they are willing to deliver it you could then use that as free fill for the bottom, then get good quality topsoil for the top foot or so, or better, soil mixed with peat moss or other organics. It used to be that if there are local stables they would deliver seasoned horse manure at a very low cost (or you could often pick it up for free), but these days because so many people are doing organic gardening, and the number of horse stables near where i live is very small, it has become expensive.
Since this is for a senior center kind of thing, you may be able to get people to either donate the material or do it at cost, if there is an Agway near you the one near me from what I hear are good about that (doesn’t mean the local one will be, though), they have things like bagged manure, compost/humus mixtures, that work great in a container I have found.