Protecting Landscapes During a Drought
Droughts are part of our natural weather cycles. But when drought conditions persist for long periods of time, they impact plant health in a number of ways. Lack of water limits a plant’s ability to produce food and stressed plants release chemicals that attract pests. Excessive heat accelerates the reproduction time of pests. There are a number of strategies that can help protect plants during extensive drought conditions.
How Plants React During a Drought
When a plant is stressed from lack of moisture, it closes the pores (stomata) in its leaves to reduce water loss. As a result, the plant does not absorb the carbon dioxide it needs for photosynthesis. This lack of water also limits the plant’s ability to move food and essential minerals around. Both of these factors limit the plant’s ability to grow and develop, so you may see stunted growth, chlorotic (yellow or bleached) leaves, leaf drop, a thinning crown, or poor shoot growth. It may take trees and large shrubs a couple of years to recover following a severe drought.
Pests and Diseases
During late fall and winter, cool temperatures keep pests from reproducing. But during a drought, warm temperatures can accelerate pest reproduction rates and the pests can quickly outnumber the populations of beneficial insects that prey on them. When plants are water-stressed they produce fewer defensive compounds, which makes them more susceptible to pests. Some plants may even begin to emit chemicals, such as ethanol and alpha-pinene, which actually attracts pests such as bark beetles. Some pests, such as spider mites and whiteflies, flourish in dry, dusty conditions and their populations often increase during droughts. Nutrients may be more concentrated in water-deficient plants, providing a substantial food source for these pests. Some plant diseases, such as canker diseases, usually affect older or drought-stressed trees and shrubs. But fungal diseases that live on dead wood can invade living tissues when plants are moisture-stressed, causing dieback in younger plants.
Drought-stressed Trees
There are many factors that impact a tree’s ability to survive a drought, such as the length of the drought, the plant species, and how well the soil holds water and nutrients. Other environmental stresses may impact the plant as well, such as competing with lawns for water, heat from pavement and buildings, soil compaction, and air pollutants. Symptoms of drought stress include wilting, leaf drop, chlorosis, leaf margins that turn brown, stunted new growth, browning and loss of needles on conifers, and eventually twig and branch dieback. Drought-stressed trees can attract insect pests and diseases. Borers are common in drought-stressed plants. As they feed on the tree’s inner bark, their tunnels inhibit the movement of water and nutrients, and they spread a fungus that can kill the tree.
Strategies for Protecting Plants During a Drought
• Choose Drought-Resistant Plants Choose plants adapted to having less-water and drier conditions. You may be able to get a list of recommended plants from your local University Extension Service or water district.
• Install Efficient Irrigation Systems
Even water-wise plants will need water to get established. Drip irrigation systems or soaker hoses for trees and shrubs can substantially cut down on water loss and be more efficient in delivering water directly to a plant. Water early in the morning when there is less evaporation, and water less often and more deeply to encourage deeper roots. In many areas, water providers offer rebates for installing efficient irrigation systems.
• Apply Mulch
Covering the soil with a layer of organic material like wood chips, bark, straw and leaves, can have a huge impact on the health of plants and the landscape. The mulch reduces water loss through evaporation, feeds the soil organisms, keeps weeds from germinating, and improves the soil’s ability to hold moisture. Apply 2” to 4” of mulch around plants, but keep the mulch 2” to 3” away from the stem or trunk of a plant.
• Use Organic Fertilizers
Applying high-nitrogen fertilizer during a drought will not necessarily encourage plant growth, because lack of water limits the plant’s ability to take up nutrients and move them around in the plant. In addition, these fertilizers can actually injure the plant when the salts build up in dry soils. To help minimize the stress of drought and maintain soil fertility, use organic, slow-release fertilizers. These will be most effective when the rainy season begins. Many organic fertilizers contain the spores of beneficial microbes, called mycorrhizal fungi, which can aid a plant during drought by helping roots access water and nutrients.
• Prune Lightly
Remove dead limbs that may harbor insect pests or diseases. Light pruning to permit air circulation may deter insect pests such as whiteflies that like dry conditions. In general, don’t overdo the pruning.
• Use Anti-Transpirants
An anti-transpirant is a compound sprayed on foliage to provide a barrier to water loss. These products have a short-term benefit but can be especially useful on young plants or new plantings. Wilt Stop is readily available at both Prickett's locations.
• Manage Pests
Keeping plant stress to a minimum through efficient irrigation, mulch, and slow-release fertilizers will help deter pests. Monitor plants frequently to identify and manage any problems as soon as they occur. If pest problems persist, use soaps, oils, and other biopesticides such as Bt to manage problems. Use pesticides sparingly to reduce the impact on the beneficial insects and mites that can help keep pest problems in check.
For More information:
Drought and Landscape Plants, article by B. Fraedrich, Bartlett Tree Research Labs. 
www.bartlett.com/resources/Drought-and-Landscape-Plants.pdf
How Does Drought Stress Influence Plant-Insect Interactions? Article by University of Illinois Extension: http://hyg.ipm.illinois.edu/pastpest/200516f.html
For more information on managing pest problems with eco-friendly solutions, visit the Our Water Our World website at www.ourwaterourworld.org
For permission to reproduce, contact: suzanne@plantharmony.org
Ten Tips for Water-Wise Gardening
In most of California, we enjoy a Mediterranean climate found in only 2% of the world’s land mass. This climate gives us mild, wet winters and hot, dry summers. But droughts are part of our natural weather cycle, and when winter rains are minimal our water becomes even more precious. Over half of our residential water is used on landscapes, so conserving water in the garden can have a huge impact on our water supplies. You don’t need to give up a beautiful, lush landscape when you create a water-wise garden. Here are some tips for creating a healthy, inviting garden requiring minimal resources and less effort and expense.
1. Go with the Low Flow - Use soaker hoses for irrigation or invest in a drip system that can cut water use by as much as 90%. Consider installing a ‘smart controller’ for your irrigation system that can save water by helping to calculate your water requirements and adjusting to changes in water needs. Be sure to check regularly for leaks.
2. Irrigate Early – Watering early in the morning when temperatures are cooler and there is less wind will minimize evaporation. This also discourages pests like snails and fungal diseases like black spot that need wet foliage at night.
3. Go Deep – Water less often and more deeply. This encourages deeper root systems that can better tolerate dry periods.
4. Get in the Zone - Group plants with similar water needs together to make watering easier and more efficient. Place pots and thirsty plants near the house where you can keep an eye on them, and use native or Mediterranean plants farther away where they may need very little water once established.
5. Mulch Like Mad – Create a 1” to 3” layer of organic material such as bark or shredded leaves over the top of the soil and a drip irrigation system. You will be amazed at what a huge difference this makes in reducing moisture loss from soil, in moderating soil temperatures, in controlling weeds that compete for water, and in returning nutrients to the soil. Be sure to keep mulch a few inches away from the stems or trunks of plants.
6. Count on Compost – Add organic matter like compost to the soil to increase soil’s ability to absorb and hold water, and to slowly release nutrients to plants keeping them less stressed and susceptible to pests. If you feed plants, use a slow-release, organic fertilizer to discourage excessive plant growth that attracts pests and increases water needs.
7. Go Native! – You will find a wonderful variety of water-wise plants in local nurseries. Look for plants that are native to a Mediterranean climate, or for California natives that grow in dry conditions. These plants are adapted to our hot summers and usually more resistant to pests. Once established, many of these plants can survive on rainfall alone. Consider replacing declining plants with a species better suited to our climate.
8. Fall into Planting – When working on a large planting project, remember that the best time to plant is in the fall when the weather starts to cool. Winter rains will help these plants establish deep, healthy root systems before they have to tolerate the summer heat.
9. Lessen the Lawn – Lawns need a lot of water, so consider reducing or replacing your lawn with water-wise groundcovers, low-maintenance perennials, or a porous hardscape. If you plant a lawn, chose drought-resistant varieties such as buffalo grass. Mow less often and raise the height of your mower blade to 3” since longer grass will shade roots, lessen evaporation, and inhibit weed growth. Your city or local water agency may offer you a cash rebate for replacing lawns and installing efficient irrigation.
10. Get Wise to Weeds – Keep up with weeding since weeds will compete for water. A drip system, mulch, and landscape fabric will help you prevent weeds.
Additional Tips for Water-Wise Vegetable Gardening In addition to a drip system, mulch, and compost, here are some ideas for saving water when growing vegetables:
• Choose early ripening varieties and plant close together in blocks instead of rows to create shade for roots and reduce evaporation.
• Choose plants that fit your growing conditions and try heirloom varieties adapted to hot climates.
• Harvest fruits and vegetables as soon as they are ready, and pick up fallen and over-ripe fruits that may attract pests.
• Grow fewer varieties and choose vegetables that will produce a lot of food on one plant, like tomatoes, squash and peppers.
For more information on managing pest problems with eco-friendly solutions, visit the Our Water Our World website at www.ourwaterourworld.org
For permission to reproduce, contact: suzanne@plantharmony.org
• UC Statewide IPM: www.ipm.ucdavis.edu Extensive information on managing pests and diseases that may affect drought-stressed plants.
• WaterSmart Gardening: www.watersmartgardening.com Plant lists, visual tours of gardens, watering guides, and resources all organized by county.
• Your local water district: Many districts provide recommended plant lists, watering guidelines, rebates for removing lawns and saving water, and water saving tips.