April provided us with some real surprises, especially that unseasonably cold and wet weather early in the month. Palo verde blossoms are now carpeting the ground, wildflowers are fading, but new leaves and flowers are bursting forth all around us. It will not be long before 100-degree days are beating down on us. So getting our gardens ready for summer is a priority in May. As we transition to warmer and dryer weather this month, we are most concerned with water management.
Caring for our gardens at this time of year requires a thorough understanding of how our plants use water. Even seasoned horticulturists have a hard time determining exactly how much water plants need. The factors that affect our gardens in late spring include heat stress, heat load related to microclimates and heat induced dormancy.
It is helpful to think about water needs from a plant’s perspective.
This brings us to the concept of evapotranspiration. ET describes water loss from both evaporation and transpiration, which is the loss of water from leaf surfaces. ET is measured in inches per day and shifts with wind, rain, humidity, infiltration rate and temperature. When we realize that 90% of applied water is lost to ET, water becomes one of our most pressing concerns as we move into the summer months. A mesquite tree can lose 13 gallons of water a day via evapotranspiration. With this in mind getting and keeping water to the extensive root zones of our plants is our ultimate goal this time of year.
By visualizing the process of evapotranspiration, we can imagine some of the struggles our plants face and understand why the summer is really a time of survival. It is also a great reminder that using native plants can mean having a garden that not only thrives but looks gorgeous during hotter times.
Native plants actually prefer a slight drought between waterings. They need the soil to dry out about 50% between irrigations. This ensures that roots have oxygen so that they are able to take up necessary nutrients from the soil. Remember, no watering schedule is perfect and at this time of year, making monthly or even weekly changes according to how plants look makes good sense.
We should all think about incorporating rainwater harvesting techniques into our landscape as drought becomes the norm for our region. Rainwater is a clean, salt-free source of water for our gardens. By observing your garden during a rain shower, you can locate the existing drainage patterns on your site. Identify low points and high points. Utilize these drainage patterns and gravity flow to move water from catchment areas to planted areas. If you are harvesting rainwater from the roof, extend downspouts to reach planted areas or provide a path, drainage or hose to move the water to where it is needed. A 1% slope is all that is needed to get water to move.
By utilizing runoff from the roof you can capture a huge volume of otherwise unused water. For example, for every 1,000 square feet of roof area you can capture 5,100 gallons of rainwater in Phoenix and 7,000 gallons in Tucson, annually. Watershed Management Group, (watershedmg.org), is a nonprofit organization that operates throughout the state. They have classes and workshops on developing rain gardens, designing rainwater collection systems, building greywater systems and much more.
It is important for all of us to remember that water is limited here and should be used wisely and consciously. Plants don’t conserve water, people do.
The trick is to give your plants enough water, without giving them too much. Growing native plants allows us to have beautiful gardens throughout the year, while using our most precious resource, water, in an ecologically sound way. Go native!
Aviva Tirosh owns and operates Dos Lobos Landscaping (firstname.lastname@example.org), providing consultation, design and installation of sustainable native gardens. Her award-winning xeriscape designs have been featured in the Tucson Botanical Gardens Home Garden Tour, Tucson Home Magazine and Tucson Lifestyle Home and Garden. Aviva is certified as a desert landscaper through the Desert Botanical Garden in Phoenix.
Photo by Aviva Tirosh