Mulching with woodchips is a great way to control weeds, retain soil moisture, keep plant roots cool, and add slow-release organic nutrients to the soil. To be effective for several years (in a low-maintenance garden), the mulch should be at least 4″ deep. If you have paths at the same level as the beds, the thick mulching can make each bed look higher than the path. At the edge of each mulched bed, gravity and ground feeding birds (scratchers) will conspire to cause the chips to slowly bleed into the paths as well. How can you keep the woodchips in the beds where they belong and yet not fall on to the paths in the garden?
It is really simple, say landscape professionals who do this for a living. Say your path is made of hard material like flagstone or concrete. Before applying mulch, first dig a shallow trench all around the bed; the trench should be as deep as the thickness of mulch you want to apply. The cross-section of the trench should be an inverted saw-tooth: nearly vertical near the path, and sloping up gently on the other side to the level of the bed.
Now apply mulch all over the bed, including the trench. The mulch will give the appearance of raising the bed by the depth of the mulch, and gently slope towards the level of the path. Walk on the chips near the edge to make sure it is packed well.
Today we got to practice edge mulching in the bed with the “NATIVE GARDEN” sign. This bed is adjacent to Park Road, and a 6″ tall concrete curb separates the bed from the asphalt. The bed is at the height of the top of the curb. So when we lay a thick layer of woodchips on the bed, it has a tendency to spill over the curb and onto the asphalt.
To solve this problem, we began by digging a 6″ deep trench all along the curb. We saw-toothed the trench, so it was sharp at the curb, and sloped upward to bed level.
We then filled the trench with woodchips, packing them tightly by walking on them, and grading it gradually towards the bed.
If our efforts are successful, the road should remain free of woodchips, and the edge of the bed should be free of weeds for many years.