While I do not encourage you to start a garden on a hill, land is expensive and maybe you ended up deciding to start a garden and you have no other choice. When we started our farm, growing vegetable for market was not something that we envisioned from the beginning. At the start of growing vegetables for market it was a bit of a challenge figuring out where to put our gardens, as the majority of our property is rolling hills. There are a couple different methods you can choose to grow on a hill. Your biggest concern should be erosion when you have exposed soil. When you combine that with a heavy rain your seeds and or soil could wash away in 30 minutes or less. Or that expensive compost that you bought-in to your garden could wash away just as quickly. But here are some of our best solutions to growing on hilly terrain.
Grass paths
One technique to growing on a slope or hill is to incorporate grass paths. You can either plan out your initial land preparation to leave the existing perennial grass in place or plant a mix of Over-Seeder Pasture Forage Seed if you are converting to a grass-path system. We use a grass-path system to feel comfortable growing parallel with the slope and whenever we have a strong, short rainstorm with the ground exposed the grass-strip does a wonderful job of catching any erosion. While there are downsides to a grass path system this is one of a couple methods that make me feel a bit more comfortable growing on the land available.
Growing Perpendicular to a hill
Another method for growing on a slope is to grow perpendicular to the slope, or imagine terraces. You could even bring in wood chips or logs to help build stronger terraces to stop an erosion with the berm or a terrace.
An easier less labor-intensive method is to look for the most level parts of your contour. Contours are S-shaped lines that have the same height across a field. It is hard to grasp at first but once you see a contour map or mark out your own line it becomes easier to recognize a contour line. The way hills and slopes are formed is through erosion and time. This is why contour lines exist and every hill has key-lines. Key-lines are where the majority of water will flow during a flooding event. Hence we want to avoid placing our gardens on a keyline but rather place tree or shrubs if we want to slow down that water. But just focusing on gardens here is how to determine your contours.
You want to determine first where your contour line is using a Hupar Laser Level and Laser Detector to make out your contour lines. If you want to go a cheaper route you could instead use a 50 ft, Clear PVC Vinyl Tubing and then add water to your initial level mark on both ends of the tube. Now using two people one end of the tube stays at the original mark while the other goes down the line to find the same mark in a new spot by lowering or lifting the tube. It does not have to be perfect here, as we are just getting an idea for where the straightest curves to your contour are located. All contours are in the shape of a S. The bottom and top of the S shape tend to be the most even level for a longer distance. This is how we decided on the location for these gardens in the photo below. The keyline here is in the middle left of the photo starting at the gate and ending up down the fence-line in the woods! This conveniently is where our fence runs and we always have deep roots in place to help slow down that water during a flooding event.
Other Considerations
As seen above we also leave 3-4′ grass strips in-between 40’x 100′ garden plots. These grass strips help re-populate bacteria and fungi after any form of tillage but more importantly stop any form of erosion. Just remember to keep those paths mowed as they will want to creep into your beds on the edges. Even thought there is a significant drop from the furthest bed at the top of the slope to the bed at the bottom, we do not experience much soil washout from crazy storms. Having tractors press down on pathways helps divert water through the path, instead of through the next bed downhill from the previous bed.
If you end up adding any sort of irrigation system, you may have to use check valves or pressure regulators as pressure will build up downhill.
Another concept to keep in mind while planning the garden is that frost settles. This means the plants at the bottom of the hill will experience frost to a greater extent than the plants at the top beds. Plan accordingly!
Adding a greenhouse to a slope needs extra attention. This could be a recipe for a huge washout if you have a crazy rainstorm. All the water will flow to the sides of the tunnel and potentially cause some major issues to your beds if oriented perpendicular to the slope. If you want to use a greenhouse on a slope consider leaving a nice grass-strip between where you want to continue the gardens. We also like to add a landscape fabric 3 or 4′ out from a greenhouse side to prevent grasses and weeds from creeping into the greenhouse during the rainy periods of the growing season. On top of that fabric you could add gravel to help discourage erosion.
