Savvy Gardeners Hydrozone

By Forrest Lockhart

UC Cooperative Extension, El Dorado County Master Gardener

Stroll through a beautiful, well-designed residential garden with a landscape designer, and you might be introduced to various key concepts of the trade, such as focal points, or garden rooms. The designer, pointing out these features in the garden, would help you visualize exactly how they work to enhance the design plan. One other concept, though present in most successful modern gardens, is not readily apparent, yet has a major impact on garden appearance and maintenance cost. In fact, you are probably using the concept to some degree in your own garden. That concept is Hydrozoning.

A definition of hydrozoning is the intelligent placement of plant species with similar needs in areas having appropriate microclimate, soil, and water conditions so that all plants in that area thrive. The most effective approach is to create microclimate zones so that plants with the highest water needs are closest to the house, with the least thirsty plants on the perimeter of the garden.

Hydrozoning techniques are best exercised when installing or renovating the garden. This allows you to start with a clean design slate. Placing plants with high water requirements close to the house has real benefits. With more water in the soil close to the house there will be a higher level of evaporative cooling in the summer, making the house and patio area cooler. This is referred to as the oasis effect. Also, with less water committed to the outer yard area, less irrigation tubing and fixtures will be required to do the job. This results in lower initial cost and maintenance.

To effectively employ hydrozoning, we must recognize that irrigation requirements vary for each plant species. Our success depends on application of the right amount of water at the right time for each plant. To do this, group plants so that your irrigation system selectively provides the right amount of water to a cluster of plants that have a common water requirement. While this is best accomplished with a drip system, a well designed system of common high-pressure sprinklers can frequently be installed to meet most needs. By not using more water than each particular plant cluster needs, you can save on the water bill. So take stock of your garden plants and prepare a list of which plants have common water needs.

But not all plant species with similar water needs thrive in a particular microclimate zone. For instance, most ferns and other plants accustomed to living under the protection of large tree canopies need an area of shade or heavily filtered sun in order to thrive. To place them in the middle of a sunlit yard, regardless of the water provided, could result in their rapid, and frequently costly, demise. The obvious solution is to expand the traditional hydrozone concept to include other microclimate conditions such as light and soil type.

It is important to have a general understanding of the type of soil in the garden. An azalea planted in hard, rocky soil with little organic material is not long for this world. So you must either plant only those species that thrive in your garden soil, or modify that soil to make it more friendly to your plants. This may involve a variety of techniques such as the addition of compost to enrich and aerate the soil, or creation of mounded planting areas to enhance drainage. Look at your plant inventory and eliminate plant groupings with widely divergent soil needs.

Take a look at your yard today. See where most of your irrigation water is going. Check if plants are grouped appropriately according to microclimate, soil, and water needs. Prepare a plan for your yard that employs hydrozoning techniques and imagine how much happier both you and your plants will be when the project is completed.