There's a famous song that tells us, "Summertime and the living is easy," but for roses, summer can be a challenge.
Sufficient water will make all the difference to their continued health and vitality. Now is the time to check your irrigation system and see it working to ensure it is getting enough water to your roses.
Rose petals have small openings, called stomata, on the underside of the petals. Water evaporates through the stomata in a process called transpiration, which keeps the plant cool by releasing water. It also creates the "draft" that draws water from the roots to the stems, leaves and other growing areas of the rose. When the roots cannot supply enough water to the plant, the stomata close to retain water.
Water is indispensable for photosynthesis and essential for the transport of nutrients to the plant. When the stomata close, photosynthesis is reduced. The resulting insufficient production of sugar causes the plant to produce fewer and smaller rose flowers in the summer. If there is still a lack of water, the plant will become further stressed and will not grow at all. It will also be more susceptible to pests and fungal diseases.
The plant needs more water in the heat, so you should water more in the summer and make sure your watering methods are effective. Don't wait until wilted leaves and flowers are a tip to water your plants.
Time to water
Watering early in the morning allows the water to soak in before it evaporates. It also minimizes fungal diseases such as black spot, rust and botrytis.
How much water to give
Add time to watering as the weather warms, and add an extra day or two of water per week during the hottest summer months. I don't think rules telling me how many inches of water to apply per week are very helpful because there are many variables that affect the amount of water our plants need. The amount and frequency of watering depends on the growing season, the outside temperature and also how well our soil retains water. Sandy soil drains quickly, while clay soil absorbs water more slowly but retains water for much longer.
How to water
Water your roses deeply so they develop a healthy, deep root system. This keeps roses cooler and better hydrated in hot weather, a huge advantage over roots left on the soil surface due to inadequate watering.
Warmer weather, Santa Ana winds and the longer summer days increase water loss through transpiration. Apply more water when the soil feels dry more than 2 inches deep, and don't wait for visual cues such as wilting or drooping leaves and flowers. A useful and inexpensive tool is a soil moisture meter, which indicates when your plant needs water.
Potteroser
Roses grown in containers should be watered deeply, rather than more often with quick bursts of shallow water. This is because our water is salty and our plants are otherwise susceptible to leaf burn. On days when temperatures rise above 90 degrees, it may be necessary to water the roses in the container daily. In warm indoor areas, place potting rollers under your pots and move your container roses to partial shade. Container roses in plastic pots can be placed in ceramic pots to protect them from extreme heat.
Effective methods of watering
Drip irrigation or soaker hoses deliver water directly to the soil and plant roots so that no water loss occurs. Overhead spraying is problematic because they can lose up to 50 percent of the water through evaporation. They are also not accurate in delivering water to each plant, especially in garden beds where roses are grown with companion plants that can block the water intended for your roses.
Access to a hose is essential when the Santa Ana winds are blowing. A quick blast of water will cool and rinse away dusty plants and help relieve dried out and drooping leaves. Do this at any time of day, provided there is enough time for the leaves to dry before nightfall, to prevent water-borne fungal diseases.
When we add organic amendments and an annual three-inch layer of porous organic mulch to our soil, we provide our plants with nutrients and better aeration and drainage. We also promote deeper root development, a cooler root zone, better water retention and a reduction in evaporation.
Ensure healthy leaves
The rose bush needs its leaves for energy production and also to provide shade for the canes and base of the bush. Therefore, avoid cutting long stems when you deadhead your roses in summer or when you cut flowers to bring them indoors. Also, pay attention and keep your leaves as disease and pest free as possible. Mottled foliage and fine webs under the leaves are signs of spider mites, which often peak in warm, dry weather. Spray jets of water under the leaves every three days for as long as they are present.
Fertilize less
We can and should fertilize our roses less often and with more dilution during the summer months. High summer temperatures cause plants to absorb nutrients faster, which can lead to leaf burn. Skip feeding your roses when the weather is very hot and make sure your roses are well watered both before and after fertilizing.
Help your roses this summer by keeping them fresh and hydrated. Continued flourishing will be your reward.
Perwich is a member ofSan Diego Rose Society, an advisory rosary and aMaster Gardenerwith UC Share extension.
