Newly Registered
Posts: 3
Joined: Fri Sep 11, 2009 9:50 am
Location: Milwaukee, WI

Raised bed on a slope - Is it possible?

Hi all, new member who will probably have lots of questions and hopes you all will be patient with me as I pick up a somewhat new hobby and would like to do it "right" at my new home.

I recently moved to a new home and my wife and I are looking to add a vegetable garden for next year. We both have our sights set on the area behind our garage but this has a slope to it. My first thought for handling this was by using retaining walls. Then, I thought why not raised beds? Seeing as I have never built a raised bed, I was wondering if I could get some help reviewing my idea.

The area is basically about 10 feet wide and 20 feet long (level measure) with the slope climbing about 4 feet along that 20 foot length. The only special consideration is that my water supply and a dryer vent are tucked into the corner between the house and garage.

Through reading up on raised beds, I understand that we want to aim for about 3-4 feet wide and 6-24 inches high (though suggestions for height seem to vary a bit) in a raised bed. These are the assumptions I'm working under as I come up with two possible designs.

1) The first design has the beds running lengthways down the slope, creating a grid of 4 beds. Each bed would be about 7.5 feet long and 3 feet wide. I'd have room for walking paths 2 feet wide by the house and between the beds and 3 feet wide by the garage. At the top, the beds would be 6 inches high. At the bottom, they would be 24 inches high.

2) I could also turn the beds so they run lengthways along the side of the slope. I'd be down to 3 beds, each bed would be 7 feet long and 3 feet wide, allowing for walking paths 3 feet wide along the house and between the beds, with a 5 foot wide path along the garage. With only 3 feet of length going down the slope, I could be more flexible with my height and have less variation.

The first design would give me more planting space but I'm a bit worried about not having much room to walk between the beds. The second gives me less planting space but still far more than I've ever had before for vegetable gardening and more room to walk between the beds. With either design, I may make one of the beds a bit smaller to allow room for a hose reel and possibly a compost bin in the corner where my water supply and dryer vent are. I'm not sure if this would be necessary, though, with the second design as I'd have 5 feet along the garage already.

I hope this all makes sense. If I could offer the sketches I have on the paper next to me, I would.

I'm thinking of using cedar 4x4 posts on each corner and mid-way through the length of the beds to anchor 2x6 cedar boards for the sides of the beds. I would then probably buy a truck load of soil to fill the beds, then be ready to start my vegetable garden.

The question I have is, before I spend time working through the details of this plan and begin buying supplies, does either of these sound like a good plan? I'm asking those with experience with the hopes that you can help me resolve any potential problems while it's still not a lot of work to do so. Are the assumptions on size/height of the beds I'm using correct? Would the paths between the beds be too narrow or unnecessarily wide? Are there any changes to these plans that you would make? Or should I scrap both of these plans and start over with a new one?

Any thoughts you can offer on this would be greatly appreciated.

User avatar
Super Green Thumb
Posts: 3233
Joined: Mon May 18, 2009 8:15 am
Location: Oregon

Just think about how your going to work the beds and reach. Think ergonomics and try not to have to bend over too much down hill. Other than saying that it looks as if your on the right track.

User avatar
Super Green Thumb
Posts: 25279
Joined: Sun Feb 15, 2009 6:04 pm
Location: TN/GA 7b

seems like your beds will need to be sort of like retaining walls, ie taller on the down slope side. You want your raised bed surface relatively flat. Too much slope = too much water drains off too fast and it's hard to keep your soil moist enough.

User avatar
Posts: 30371
Joined: Thu May 01, 2008 7:21 pm
Location: Zone 6, NJ (3/M)4/E ~ 10/M(11/B)

First, you could take photos of your sketches and then post them here for us to see. Directions for posting photos are [url=https://www.helpfulgardener.com/forum/viewtopic.php?t=3724]here[/url].

Now, I have a similar situation, and based on my experience. I have some suggestions:

(1) Which way does the slope face? Mine faces SW at about 5~10º. That, coupled with the fact that I did NOT want to dig into the slope led me to build my raised beds following/hugging the slope. They are positioned with long length down the slope. Uprights contoured to the slope are plumb but the long sides are not level as they hug the slope.

(2) Water runs down the slope. My neighbor on the other side of the property line complained that when I water heavily, the water pools on his side of the property. To help circumvent this, I added a 24" bed at the end of each path (my raised beds look kind of like the letter E now). Now, what happens is that water pools at the bottom of my paths.

#2 has a couple of ramifications. If you build your beds parallel to the contour of the slope, the water will pool on one side of the path against the length of the bed. Sequestering the water this way would be a good thing if you tend to have drought conditions as I do -- I think if I were to do it again, I might re-design my raised beds this way -- but if you tend to get over-abundance of rain, then ALL your beds might get too soggy.

On the other hand, If you build your beds lengthwise down the slope, you will have a very well drained upper end and very well watered lower end. I found this to be very useful as long as I take the watering needs of the plants in to account when planting. Potatoes, carrots, etc. root vegs do very well at the upper end, water-loving vegs like cucumbers, melons, and pumpkins do well at the lower end. (The excess water at the bottom of the paths helped to carry the water-loving plants in the main long beds for days after rain/irrigation)

For next year, I'm going to build up the beds at the bottom of the paths into taller squares boxes (my paths are 24" wide) to help handle the excess moisture. Although the honeydew melon did very well, and tomatoes managed OK, carrots were drowned and bush beans didn't do so well.

I built a 4'x4' 24" raised bed (soil filled to 18") on upper end of one of the the long beds. It avoids waterlogged conditions even in the early spring thaw, and when covered with plastic sheeting, doubles as a cold frame because of the slope angle. (I have sweet potatoes and corn growing in there now)

Also, I have very clay subsoil. No-till, sheet-mulched, raised bed on the slope sheds the water and prevents any heavy-soil problems.

Newly Registered
Posts: 3
Joined: Fri Sep 11, 2009 9:50 am
Location: Milwaukee, WI

Thanks all for the great tips.

Tomf, good point about ergonomics. That might actually argue for beds that run parallel to the contour of the slope so, while keeping the tops of the beds level, they are all at a more comfortable height.

Rainbowgardener, this is along the line I'm thinking of. I was actually originally thinking of building two retaining walls for this area and planting the vegetable garden on a tiered garden but I thought raised beds might work better. I'm definitely looking to do something to lessen, if not eliminate, the slope in the areas where planting will be done.

Applestar, lots of great tips in there. The slope faces north, which I originally thought would be a major issue for a vegetable garden. However, three doors down from my home is a vegetable garden completely blocked from the south, with a garage to the southeast and a two story house to the southwest. They are gardening in a raised bed (on level ground) and the garden is doing great.

Fortunately, on the downhill side from my home is a hay field so some drainage to that won't be a problem. However, our long term plans call for a patio directly below this garden so I'll definitely keep drainage in mind and this would again argue in favor of beds running parallel to the contour of the slope.

Our watering situation varies by season. Spring is usually wet before we typically get a dry July and wet August, leading to a semi-dry fall. At my old home, we had a few tomato plants and would almost never water. Soil is definitely a clay/rock mix. Whenever I dig, it seems like more rock than clay. :P

Again, thanks all for the tips. Things I would never have thought of until too late.

User avatar
Ozark Lady
Greener Thumb
Posts: 1862
Joined: Tue Jan 05, 2010 5:28 pm
Location: NW Arkansas, USA zone 7A elevation 1561 feet

I also have raised beds on a slope. My hillside drops about a foot every 4 feet. So with the beds running across the slope I have one side that is 1 foot higher than the other, which we just dug it down a bit deeper to fit the timbers in. But the upper timber is at ground level and the lower timbers all show.

We tend to have a mixed bag of a season. In early spring, it rains constantly. But, you hit July and August and drought is fairly common.

We double dug the beds, and after removing the tree roots, and sifting out the larger rocks, when all the dirt was returned it was a sunken bed. I picked up several pick up loads of rabbit manure, and hay, and pulled the dirt out again, layered it back in there, and had a decent raised bed. They were not particularly fertile... I think my hubby and son, added so much manure that they were almost toxic. So, I started adding bags of potting soil, and just waited a year. The next spring, I started out with sunken beds... again! So, I amended them with leaves, manure (not the truck loads this time, just my barn manure divided up amongst all 9 beds) But, I didn't get all the beds amended back to being raised... some were still sunken below the edges of the timbers!

It ended up that was okay, I planted potatoes in one sunken bed, and covered them with hay and leaves, and they gave me a bumper crop that was easy to harvest.

And the sunken beds, didn't dry out when drought time came, the clay in the surrounding soil, thought my beds were ponds and held the water in for me... worked great.

So, I now try to raise a couple beds, use some sunken and fill with mulch as the plants grow. And some, I just let stay sunken and plan on those guys getting me through the drought, when the raised guys just can't stay wet enough.

Does anyone else use "sunken" raised beds, with timbers on a slope?
The timbers do help keep the amendments in place, until the organic content breaks down, and is in place to keep the mulch where I want it, but soil seldom touches the timbers on the lower side.

Return to “Raised Bed Gardening”