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The Secret to Getting A Drought Tolerant Plant – Drought Tolerant
By Richard Flowers, ACCNP-Green Thumb Nursery-Ventura
To many people, a drought tolerant plant means that it doesn’t require much water. Though the statement may be true, their is more to it than that . A drought tolerant garden plant can earn that designation and acquire the ability to survive on average rainfall with little or no supplemental water once established. These plants tend to have characteristics that minimize water loss from the leaves and/or maximize water uptake by the roots. These characteristics include deep roots; gray leaf color, small, succulent, hairy, or waxy leaves; or the ability to go dormant during drought. Drought tolerant plants lose less moisture from their leaves through transpiration and are more tolerant to dry conditions. Examples of these types of plants include many types of Salvias (sage), Rosemary, Lavender, Texas Sage, many California Natives, Mediterranean, South Africa, Australian plants, and Cacti /Succulents. These plants take advantage of moisture deeper in the soil profile to avoid drought stress longer. Root depth is genetically determined but plants will only develop deeper roots if moisture is available in the rooting zone at the right depths. Roots will not grow deeper in search of water. Roots only grow where there is moisture and oxygen available in the soil. To promote deeper plant roots, water when halfway down the rootball is dry.
Getting new plants established in the ground is critical to achieving drought tolerance and the ability to withstand being drought stressed. Plants are not drought tolerant until they are established in open ground. The majority of plants planted in containers are not drought tolerant. It may take 1year or longer for a plant to become established depending on conditions and they way the plants are cared for. These conditions include soil type, weather, type of plant material, condition of plants, and so forth. It is important when selecting plants to choose plants that are healthy, with a well established / developed, and vigorous root system, stems, and branches. A plant with girdled, kinked, circling roots or plants that are root bound will result in a plant growing poorly and establish slower. Some plants by nature are slower growing and therefore take longer to establish. The time of year determines how fast plants become established. Most plants grow slower during the winter however many plants put root growth on during the this time and top growth during the spring and early summer when most people want to plant them. Most Mediterranean, Australian, South African, and California native plants put root growth on during the fall and winter and this is the preferred time to plant and to take advantage of the rainy season and to get them to established easier. Fresh top growth occurs during spring and is the time when most people are eager to plant, though young plants can be stressed going into a hot summer. Some plants prefer to be planted during the spring, others during the fall/ winter, and still others any time of the year especially in moderated coastal conditions. The conditions the plants are growing in determines how long it will take to become established. Factors such as soil, weather, terrain, ands site conditions all play a key role. Your care and maintenance practices also have a bearing on establishment rate. These practices include but are not limited to watering, fertilizing, pruning, planting techniques, competition of other plants, and choosing the right plant for the right location.
Many people are guilty of the practice of watering their plants for five minutes every other day by a pre programed irrigation system just because and they wonder why their plants are not thriving. By watering at this interval, the plant roots will be close to the surface and dry out quicker. The key to achieving drought tolerance is to water plants correctly and I will provide you some tips on how to attain this goal. It is critical to understand that there is a relationship between plant roots and water. If the moisture level in the soil is shallow, the roots will be shallow. If the moisture level in the soil is deeper the roots will be deeper. Understanding this concept means it is best to irrigate your plants longer and slower so the water can seep deeper into the soil therefore the roots of the plants will position roots deeper. Plants with deeper roots have more anchorage in the soil making them stronger. Most drought tolerant, healthy plants that are very mature and well established have the ability to extend their roots several feet or more in the soil if watered properly. These plants can endure the effects of drought stress much better than plants that have developed shallow roots. During hot, dry, and windy days if the plant roots are shallow they will dry out faster, wilt, and demand more water. Plants with shallow roots are weaker and more susceptible to insects, diseases, and drought stress. If you have well established, mature plants, you may wan to consider this effective watering technique. Construct a watering basin around each plant. A water basin is a berm of soil up to 6 inches high all around the root ball. When you irrigate, fill the basin with water. The water will then percolate into the soil exactly where the plant needs it! Fill the watering basin up with a slow trickle of water so that water permeates the entire soil, filling up the basin without running off. It should take hour or two to fill up. Once the water is done seeping through the soil, repeat the process again. This is a very effective method to thoroughly water your plant material deeply. This watering method is usually done once or twice a month depending on conditions when the plant needs it. This technique can also be used for new plants with the realization that you need to water the them more often than that of mature plants. The goal when watering your plants is to provide good thorough soakings (not a light spray) where the water seeps into the soil 1 to 2 feet because this where most of the roots are for mature plants.
It is a common practice for many homeowners and gardeners who utilize drip irrigation to water their plants and have one emitter per plant. In many types of soils, water movement is downward and not out. With that theory in mind, by having one emitter per plant is likely ineffective at watering your plants efficiently. In this case you will be watering one area of the plant and the other areas around the plant roots are still dry. With that being said, it its wise to irrigate you plants uniformly by placing multiple sprinklers around the plant on all sides as opposed to just one single emitter. Space them uniformly around the plant and remember to adjust the watering area as the plant matures. The goal is to have water to be uniformly applied around the plant. Another alternative method you may want to use is a soaker hose. Simply spiral the soaker hose just outside the plants canopy where all the leaves and branches extend (also known as the drip line ). of the plant inward 2 to 3 times. Turn the hose on and the water will seep out slowly for several hours. Make sure you have a pressure regulator connected to the hose faucet because this special type of hose runs on lower pressure.
It is important to note that newly planted plants and younger plants do not have an extensive root system yet, their roots are still close to the plant therefore they are not drought tolerant. When a plant is labeled as “drought tolerant” and is newly planted its roots extend only as far as the potting soil in which it came in meaning this is where you water. Over the next few months, new roots will begin to grow into the surrounding soil. Usually during the first year, any new plant will need regular soil moisture to establish a root system. This requires you to be vigilant in monitoring the young plant, the temperature, the wind, the amount of rain, and supplying moisture when the plant needs it. As the plant matures the roots expand and so does the watering area. Growing a large root system the first season will help the plant survive the next year as irrigation is reduced. When a plant is fully mature irrigation should be applied at the drip line of the plant. As the plants mature by the second summer you can reduce irrigation frequency but increase the amount of time you water. Apply water slowly so that it penetrates into the soil and does not run off. Water should be applied over a long period to penetrate the entire root zone. If runoff is a problem, run short applications of water, let the water soak in and repeat. It is critical to to understand when you should water your garden plants. The simplest way to address this is when the plants needed depending on conditions. If the conditions are hot, dry, windy, plants always demand more water. Plants that are young or newly planted always demand more water than plants that are more established. The local terrain and microclimates also determines when you water your plants. As an example, if plants are planted on the top of a slope, they may need more water than plants planted on the bottom of a slope. If the plants are in a shady area they oftentimes need less water than plants planted in a sunny area because evaporation is higher in sun exposed sites. If you have a sandy soil, plants require more frequent, shorter watering intervals because these soils do not retain moisture. On the other hand, if your soil happens to be more clay, theses types of soils drain slower and therefore require less frequent but longer watering. Watch for wilting and water if needed. It is always encouraged to check your plants frequently to see if they actually need water. If you are going away for any period of time, make sure you have someone responsible to check the plants to see if they need water and don’t rely on irrigation timers to do the watering for you as they can malfunction. Make sure your irrigation timers and the entire system is in good working order to water efficiently.
An effective way to determine when a plant needs water is by probing the soil to determine where the moisture level is. Don’t just look at the top of the soil, it is what is underneath that counts. Consider using a bamboo stake or some other implement and sink it halfway down the rootball at the outer edge on all sides of the plant. If soil water sticks to the probe the plant does not need water at that time. On the other hand, if soil water does not stick to the probe the plant does need water at that time. After doing this practice and performed several times you can then establish more or less when you need to water. Handheld moisture meters are ineffective to use for this application.
Deep watering means that when you water the soil it is saturated (wet) to half way down the root depth of the given plant. Generally for most mature, well established shrubs and trees the roots are in the top 1 or 2 feet of soil but often times much more than that. In that example, you should water to a depth of 6” – 1 ‘ slowly mimicking a slow steady rain.
If you already have plants in the ground for many years and want to make them stronger and able to withstand the pressures of drought you can try to gradually wean or accustom the plants to longer, deeper, and slower soakings. As an example: if your plant is already accustomed to being watered for 10 minutes everyday, then you would need to increase the time/ days gradually over a period of time ( a few months or longer) until you reach the bench mark. As a rule of thumb, most well established and mature drought tolerant trees need once a month or longer of deep watering. Shrubs that are drought tolerant and well established need deep irrigation every other week . Drought tolerant, well established perennials should be watered once a week or less often and deeply. Please note, there are exceptions to the rule from the above statements. Watering should be done depending on conditions and when they need it which always takes precedence.
Part of the process in making your plants drought tolerant is by improving your soil and mulching to improve its quality. Did you know that a 4 to 5 inch layer of mulch can reduce water evaporation from the soil up to 50 to 60%, ! Thus by having several inches of mulch you will have better use of irrigation water. Mulch also supplies much needed nutrients, improves the bio activity, and encourages beneficial mycorrhiza fungi in the soil making your plants more drought tolerant and use water more efficiently. Mulch also helps keep down weeds that compete for water and nutrients. When applying mulch, make sure the mulch is not touching the main stem of the plant. Always keep lasting supply of mulch around the plants. Mulching is more critical for new plants than adding soil amendments, the reasoning is, once the plant roots grow through the nice, amended, fluffy soil and into the native soil, they may have a tough time adjusting to the adverse soil conditions. Please note, when watering mulched plants, it is wise to water enough so the water seeps down through the layer of mulch and the soil. When planting, it is advised to plant new plants by digging the planting hole 2-4 times wider but no deeper than the rootball to be planted. In most cases, the soil dug from the planting hole is sifted to eliminate clods or chunks of soil. This backfill is used to place around the newly planted plant. Many types of native soils are lacking organic matter therefore you can use a soil amendment. It is recommended to be lean i.e. add no more than 50% amendment mixed uniformly with the backfill (native soil) and don’t forget to amend the surrounding soil as well. Never over amend the soil, it can ruin its structure. A healthy soil with the addition of a little organic amendments improves drainage, bioactivity, retains moisture, and makes the plant have better use of water. Throughout the year you may want to consider using organic fertilizers to aide in soil health.
By watering your plants correctly and improving your soil, your plants will be happier, stronger, and take less water therefore using it more wisely and not wasting it. And remember this principle: the right plant planted in the right place at the right time with proper care equals a healthy drought tolerant plant.
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