The Virtue of Planting on Hill Mounds
Gardener’s Notebook by Joshua Burman Thayer
In the photo on the left, an olive tree gains benefits from being planted on a mound. On the right, numerous plants are nestled into a raised berm that helps direct water flowing down a hillside. Photos by Joshua Burman Thayer
Some plants have evolved to live on hillsides. They do not generally like to be in constantly wet soils and prefer that storm water pass them by and drain down to the flats below. This can be difficult in clay soils that tend to pool water in winter. And it can be difficult as well in daily watered gardens.
Avocado, olive, grape, fig, and mulberry are examples of plants that prefer the drainage pattern that a hillside provides. They grow well in the Bay Area’s mild Mediterranean climate, and we benefit from the fruits they provide. But when we plant them, we should keep in mind that they evolved in hilly environments.
Even if you have a flat yard, you can mimic hilly contours simply by the way you plant these trees and vines.
For any of the above plants, follow these steps:
- Start with preparing a mound-planting mix that combines the local soil you dig out at the planting site with equal parts bagged planting mix and rocks. This mix allows for an aerated root ball, and while in the dry season, this makes little difference. But when the wet season arrives, this rock-heavy mixture will allow for more air space to keep the soil from reaching full saturation in wet winter months.
- Dig a hole that’s two to three times the size of the pot or root ball of the plant.
- Backfill the hole with local soil so the plant will sit higher than the surrounding ground: two feet higher for 15-gallon size pots or 12 inches higher for 1-gallon or 5-gallon pots.
- Rake excess soil away from where the tree will sit.
- Un-pot the plant and open its roots a bit by massaging the compacted edges.
- Place the plant centered in the mound.
- Since one lone plant set so high would be vulnerable, we must now create a dome of soil mix around the planting to stabilize the area. Shape the soil mix around the plant to create a donut shape.
- Hand pat this soil to make it sturdy, smooth, and even all the way around the tree. Then take a rake and taper the sides gradually down to the level of the surrounding ground.
- Rake away area’s excess soil/mess.
- Now you have a mound. Water it deeply.
Note that you can follow the same method and pour soil between plants to make a whole berm or island planting.
By planting these plants higher above the winter wet clay, we set them up to respire and live more comfortably.
Happy Gardening!
Joshua Burman Thayer’s Gardener’s Notebook is filled with gardening advice for every season. Visit the whole collection of articles here.
Get expert help with your garden from Joshua Burman Thayer at 510.332.2809. Learn more about food forests and permaculture landscape design at nativesungardens.com and from Joshua Burman Thayer’s new book, Food Forests for First Timers.
