In the depths of winter, our thoughts turn to spring in the landscape. We think about ordering new plants, consider changing or adding elements to our yards. Many design elements make major impacts on our landscapes. Earlier blogs have discussed water features and planters as effective design elements. Another effective landscape design element is mounding.
The practice of mounding (creating an elevated area in the landscape), if carried out correctly, can be an effective solution to problems in the landscape. Mounds can effectively lower the water table, provide a screen, create micro environments, alleviate drainage problems and create interest in the landscape. Mounds are not clearly understood; they are more complicated than simply a pile of soil that has been dumped. Before undertaking the construction of a mound, questions need to asked: Why do we need a mound? How big should it be? Are we going to plant on it? And if so what are we going to plant? How is it going to impact the rest of the landscape? Do we have enough room?
Most mounds that you see are long and narrow and high, often too narrow. Mounds should be wide enough and long enough to allow plantings on them. Planting trees on narrow, high mounds is a recipe for disaster.
Remember, when you construct a mound you effectively lower the water table, so having irrigation available if you plan on planting the mound is essential as water will drain more readily. Wind velocity at the top of the mound will be greater as well. By creating a mound you may be diverting surface water to areas that do not require the extra moisture, causing areas to flood, but you can also use mounding to divert water to an area that is in need of more water.
Ideally, a mound should be fairly wide and preferably not in a straight line. It should vary in height over its length and it doesn't have to be very high. The higher the mound, the wider it should be. Consider the slope of the mound; if it is too steep plants will grow poorly and the mound will undergo erosion. If the mound is grassed, it may need to be mowed at some stage as well.
The selection of plant material is an important consideration. Pines, spruce, and firs do not allow the wind to pass through them, basically acting as sails, so in high winds they are prone to be blown over. Planting evergreen trees on poorly constructed mounds is not a sound practice. Confine them to areas that are more level. Instead, consider planting medium-height shrubs, for example viburnum, yew, holly, or lilac. If you want to plant trees on a mound, deciduous varieties would be more suitable. If you really want evergreen trees on your mound, choose varieties that are not very tall and are slower-growing.
As there are many technical considerations involved in the construction of mounds, the average gardener may benefit from consulting professionals for anything beyond the most basic mound installation.