The summer months draw our attention to our roses’ need for more water. Water is indispensable for photosynthesis and vital to the transport of all the fertilizers and amendments that we add to the soil to feed our roses. In short, adequate water is essential to produce healthy, beautiful roses. But of course, it is imperative to make every valuable drop count and avoid water wastage.
Rose leaves have minute openings on the bottom of the leaves called stomata which take in carbon dioxide and release water. As water is released from the stomata, the roots suck more water up into the plant. On hot summer days when the roots cannot supply sufficient water to the plant, the stomata close down to preserve water. With the stomata closed, the intake of carbon dioxide is shut down, which stops the production of sugars and the process of photosynthesis.
For this reason, rose blooms are often fewer and smaller in summer. The best way to overcome this is to increase watering and to ensure that our watering methods are efficient.
Efficient methods of watering
It is crucial as summer approaches to check your irrigation system and make sure it is working properly. You will need to add minutes to your irrigation run time as the weather heats up, and add an extra day of irrigation in the hottest summer months. Drip irrigation or soaker hoses water directly to the soil and the plants’ roots so there is no water loss. One very good drip irrigation system is Netafim which consists of tubes with evenly spaced internal emitters that do not get clogged.
Overhead sprays are problematic for a number of reasons. Not only can they lose up to 50 percent of water to evaporation, but they often waste water by irrigating sidewalks and walkways instead of soil. In addition, spray systems are not precise in delivering water to each plant, especially in gardens where roses are grown with companion plants that block water to our roses’ roots.
Access to a hose is essential when Santa Ana winds blow. A quick blast of water will cool down our roses, wash off dusty leaves and help relieve dehydrated and drooping leaves. The same action helps wash off aphids or spider mites. Do this at any time of day provided that there is sufficient time for the leaves to dry off before nightfall in order to prevent water-initiated fungal diseases.
How much and when to water
The amount and frequency of irrigation depends on how well our soil retains water, the growing season and the outside temperature. Applications of additional water are needed during hotter weather and Santa Ana winds. During active growth, garden roses usually need a deep watering to a depth of 5 to 6 inches.
A useful and inexpensive tool is a soil moisture sensor meter, which provides a moisture reading, letting you know when your plant needs to be watered.
Irrigate in the early morning hours to prevent evaporation and fungal disease. Water when the soil feels dry more than 2 inches deep; don’t wait for visual clues such as wilting or drooping leaves and blooms.
Roses grown in containers should be watered deeply and less frequently, rather than more often with quick bursts of shallow water as our water is salty and our plants will otherwise be susceptible to leaf burn. On days when the temperature is over 90 degrees, you may find it necessary to water container roses daily.
Promote water retention
When we add amendments to our soil, we provide our plants with nutrients, better aeration and drainage. We also promote deep root development and improve the soil’s water retention which reduces the need for watering. The application of 3 to 4 inches of mulch annually adds water retention capacity to the soil.
Maintain healthy foliage
The rosebush needs its leaves for the production of energy and also to provide shade for the canes and the base of the bush. For this reason, when you cut blooms to bring inside or deadhead your roses in the summer, avoid cutting long stems.
Also, be watchful and keep your leaves as disease and pest free as possible. Mottled, speckled foliage and fine webbing under the leaves are evidence of spider mite infestations which often peak in hot dry weather. Spray jets of water under the leaves every three days while they are present.
We can and should fertilize our roses less frequently and more dilutely in the summer months. Hot summer temperatures cause plants to draw up nutrients faster, which could result in leaf burn, so avoid feeding your roses when the weather is very hot and always make sure your roses are well watered both before and after fertilizing.
Summer can be challenging for your roses. But keeping them refreshed and hydrated will get them through the hot season beautifully.
Perwich is a member of the San Diego Rose Society, a Consulting Rosarian and a Master Gardener with UC Cooperative Extension.
