I've read through some of the posts from people who share my situation: I'm planning on building raised beds on sloping land for a market garden. The consensus is that the beds should be built on contour.
I'm having trouble wrapping my head around the spacing between beds. If I follow the contour lines exactly, wouldn't the beds or space between beds be wider or narrower in places? In order to achieve even spacing, should I use some "average" or standardized contour lines?
If you're willing to do some land shaping (leveling some spots and filling in others) anything but a steep slope should be easy to get close to consistent. Map all the beds ahead of any digging and then if there are any areas where there is too much change it might be a good spot to have an access path between rows of beds. Does that sound like it might work for you?
It would be good to get an idea of how much slope you're talking about.
Past a certain point, you want to build terraces, or your lovely raised beds stand a very good chance of getting saturated in the first really heavy downpour and going to visit whatever or whoever is at the bottom of the slope.
The fact that the spacing between raised beds on-contour will vary is an aesthetic consideration, the choice to put them on contour is a hydrological one.
You can, as Casie suggests, do some land shaping, but is it that important to you to have perfectly parallel beds? I would personally value sediment and water capture and storage over how it looks.
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Casie, I do like the idea of row paths through the areas that change the most. In fact, this might relieve some of the burden a bed might have during a heavy rain, as Chris points out.
Chris, the hillside has somewhere between a 5 and 10% grade and it's fairly consistent. We get 15" of rainfall per year but we're due for an El Nino according to forecasts. The concern of washout, therefore, is a real one.
Deeper pathways and high raised beds, with pathways at the points where slope increases considerably, might reduce blowout during heavy rain events, correct?
Here in the Pittsburgh area a 5% slope is considered level. A 10% slope is just that a slope. Between the front of my porch and the back of the house is 47 feet and it drops 8 feet. There's a door in front and in back is a basement door and a garage door. That's a 17% slope. We get close to 40 inches of rain a year and we're 6 to 8 inches above normal in rainfall so far this year. There's been a lot of hillsides slide this year, but those are usually really steep hill sides, more like cliffs. I'd say that if your worried about runoff you bury a 4" pipe down the slope. With a 10% slope and a good stand of grass the grass should hold the ground.
If you're in LA, then I'd guess your real problem is you don't have rainfall to support a good stand of grass, but if you have a garden in this spot then just water the grass while you're watering the garden. With water and a half inch of mushroom manure a year, or some other product, whichever you prefer, I think you'll be OK. But I don't know how wide your beds are which will block the rainfall runoff and channel it potentially into a narrow spot. If you have 8 foot wide raised beds and the original contours in between each pair of raised beds, then I think you'll be OK, with that good stand of grass.
If I'm wrong about my math I apologize profusely.
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