Waterwise Gardening
Water is an amazing resource that needs to be managed as much as any other natural resource. People with big brains get together to figure out how much water is available and where it is going and whether or not we have enough to do what we need to do. Managing this resource starts with the knowledge of where the water is coming from. Surface water is easy to see; it comes from the lakes, rivers and streams in our area. The snow pack can be measured and calculated for its water content. Most of the water that normal homes use here in North Idaho comes from the Spokane Rathdrum Prairie Aquifer - a large underground lake that spans from western Spokane up to the bottom of lake Pend O’reille. Multiple studies have shown that our area has been experiencing a drought for several years. In order to have enough water for everyone, we should all learn to conserve the water resources we have.
Temperature
Remember that the temperature of the soil and how much wind is blowing are the primary drives for water loss in the ground. Overnight temperatures are a good indication of how cold your soil is. For example, if the average overnight temperature for the week is 56͒ your surface (top foot of soil) soil temperature should be within a few degrees of this number. Keep in mind that the average deep soil temperature (6ft deep) here in North Idaho stays at a consistent 45͒ but the surface temperature varies based on overnight temperatures, wind speed and water concentration. Soil temperatures that are less than 40͒ can hold water almost indefinitely here in the inland northwest because of our humidity and frequent precipitation. Most gardeners here in North Idaho don’t need to start watering their whole yards until the average overnight temperatures exceed 48͒. This knowledge can also affect the time of day that you water. Gardeners need to wait until the soil temperature has dropped to minimize water loss from evaporation. Soil is usually cool enough to hold more water between the hours of midnight and about 10am here in the inland northwest. Soil temperature is also the reason that hanging baskets, pots and raised beds need more frequent watering. Because their root mass is exposed to more sun and wind, the soil temperature is hotter than the ground, drying out plants faster. You can insulate raised beds, double pot plants or move hanging baskets into the shade during the hottest part of the year to reduce the frequency you need to water.
Keep in mind that the wind picks up around sunrise and sunset. Make sure your sprinklers are done by sunrise so those morning breezes can dry the leaves of your plants to prevent disease and sunburn. It is not a good idea to water when the wind is present. Steady wind as low as 4mph with our average humidity can result in a water loss of up to 25%! Wind driven evaporation is as high as 47% in arid areas!
Mulch: Blankets and Food
This is one of the reasons why mulching your garden beds (even your lawn!) is important. A good layer of mulch in your garden beds acts as an insulator, lowering the temperature of the soil. As we just learned, colder soil holds water longer! Mulch has other benefits, however. Organic (not stone) mulch decomposes and adds nutrients back to the soil. As those organic particles get smaller they become humus, the smallest particle of organic material in soil. Humus helps soil to retain water in the soil instead of your applied water running straight through all the sand and gravel we have in our area. Mulch can also help to break up clay soils both physically and chemically. Humus also feeds the microbiome of the soil making everything you plant healthier. Mulch has the additional benefit of helping to reduce weeds! Remember that these ideas apply to organic mulch, not decorative stone.
How’s Your Dirt?
Soil is composed of decomposed rock (sand, silt, clay), organic material, water and organisms; usually at 50% per volume. This percentage varies with the type of soil. To balance the composition of soil, you need the proper mixture of these soil components for the type of plants that you hope to grow. Succulents and Lavender, for example, enjoy a higher percentage of sand while Ligularia likes rich, wet soil. You can try digging a hole and filling it with water. How quickly the hole empties and dries out can give you a hint of how much sand, clay or organic material your soil contains and how you may need to amend it to ensure it holds the right amount of water. Organic material can act like a sponge, holding water in sandy or gravely soil while it can also help (with sand) to break up pockets of clay soil both mechanically and chemically.
Soil is an ecosystem all its own. It has great biodiversity and a food web with amazing interdependency. This ecosystem is balanced in a healthy soil system. Disturbance of the soil, severe drought, flooding or excessive use of chemicals can throw the system out of balance to the detriment of the plants we try to grow. Reintroducing compost, mulch and good management practices can improve the soil’s ecological balance. Using mulch that decomposes will inoculate the soil with beneficial microbes and mycorrhizae by using organic compost can also help improve soil. It is usually recommended that gardeners test their soils before fertilizing so too much is not added. Excess fertilizer just washes away and ends up where it shouldn’t be. NPK and pH tests are available at the nursery. For testing other elements, chemicals, pharmaceuticals and heavy metals, soil tests can be mailed to testing agencies or the USDA.
How to Water
Water is critical to any landscape. Some water is even necessary in the soil to maintain decomposition and to dissolve minerals from rocks and acids from decaying plants. Water can help evenly distribute chemicals in the soil. Too much water, however, can wash away all of your hard work, since most of the nutrients that plants need are water soluble. Excess water in the soil can also suffocate the roots of plants, causing them to rot. How we water our plants is critical. While all plants need water, it is important to realize that one of the primary drives for root production is dry soil. Dry soil sends a signal to the plant to direct more energy into root production (Help! We are running out of water!). It also stimulates roots to reach deeper into the ground. Not only does this extend the root system below the hot surface during summer months, but it also gives roots greater access to minerals. The general rule of thumb is to deep soak the ground (to the bottom of the root ball) and then let the top 15% of the root mass dry out completely. Soaking a plant does not mean to dump a bucket of water on it. Drought stressed root balls shrink and become water repellant, just like a dry kitchen sponge. Water should be applied slowly to saturate the root mass and allow it to hold as much water as it can. You can use drippers, put the hose on a trickle or drill small holes in a bucket to slowly water plants. Keep in mind that in September our overnight temperatures go back down (cooler soil!) and we need to reduce the frequency of our watering. In addition to triggering more root growth, drought stressing plants in the fall can help them go dormant so they don’t get hit by our frequent, early frosts. By October, you shouldn’t be watering hardly at all, regardless of daytime temperatures.
Native Plants
It takes approximately 2-3 years to establish a root system whether starting from scratch or retraining an existing root system. By frequently drought stressing your plants in the spring and fall when the overnight temperatures are low, we can establish a landscape with deep roots that only needs to be watered a few times during the hottest part of the year. Having soil with a good balance of organic material and a healthy layer of mulch will help keep the proper amount of water in the soil where roots can reach. Xeriscaping is the science of using low water plants and native plants in your landscaping to reduce water consumption. Using plants with grey/green leaves, narrow leaves, waxy leaves or no leaves (needles or scales) will all help with water use. Native plants will often use less water and require less fertilizer than plants that come from other parts of the US and elsewhere around the world. They are accustomed to our native soils and will require less work to establish. Native plants are also important for native species of insects and animals. Less fertilizer means less overall pollution to the environment. Native plants generally tend to need less maintenance and have deeper root systems. They can be just as aesthetically pleasing as non-native species with less work. Keep in mind that if you put a native plant into your flower bed and water and fertilize regularly, it may become just as high maintenance as an introduced species. Native species are also the regular food for the critters that live here and will be browsed on. Native plants should be given some “tough love” and encouraged to fend for themselves as much as possible. Proper soil, good watering practices and the right plants can help us conserve the water we use while still enjoying a thriving landscape.
Maintenance
As much as we would love to just “set it and forget it” one of the best ways to conserve water is to keep an eye on your systems. Check your sprinklers twice per year to check for breaks, overspray or misdirected sprinklers. You will need to top off the mulch in your beds at least once per year. Remove plants that are using up too much water and replace them with lower water species. One of the most critical jobs is going to be watching the weather and turning off the system when it rains, when it’s overcast, too windy or when the overnight temperatures go down. After 2-3 years of babysitting them, your plants will need less water and upkeep, but you will still need to feed them and maintain your sprinklers. Every 5 years or so your soil should be retested to ensure that your fertilizer requirements haven’t changed.
One last note, capturing and storing rainwater for use in your garden is legal in both Washington and Idaho but it must not be taken from existing streams or ponds and it cannot be gathered from a building constructed for just that purpose. Your collection of water cannot interfere with the water rights of others. Be sure to check your local rules before collecting rain water for your garden!
