How to care for roses during a heat wave

As I look back over my previous articles, I noticed that since 2013 we have what I suggest is a new normal of high temperatures for August-September. I checked the weather projections and learned that temperatures for the next 7-10 days for Southern California are for over 100 degrees.

If you are participating in my prescribed practice of allowing a summer rest for your roses, you still have several weeks to take it easy before a mid-season pruning. As a wise man once said, “Predicting things is difficult, especially in the future,” but one can only assume it will look a little like the past, especially with the weather. So I'll give it a try. If a mid-season pruning is done after the second or third week of September, you can possibly have two more bloom cycles this year. If you would like roses for a special occasion, count back 6 to 7 weeks from that date; the date you land on will be when you need to have your pruning accomplished. Remember, a mid-season pruning is light, removing the many branching – that is, any point where many stems of blooms came from near one location on a cane – back to the main cane to an outward facing bud found at the base of a leaf where it joins the cane. Cutting back to the first five-leafed leaf will result in quicker repeat of blooming.

During periods of sustained high temperatures it is necessary to ensure plants receive adequate water to stay hydrated. It takes only a few days in these temperatures without sufficient water for a bush to succumb. Assess conditions every morning. Look for wilted or dry crisping foliage. Sometimes if you discover it soon enough dousing with plenty of water in addition to plenty of water to the ground may save the plant. If you wait to inspect until the afternoon or evening, it may be too late or you might not get a good assessment of the plant’s condition. After a hot day, most plants can appear wilted while still receiving sufficient hydration. Also inspect your irrigation system to make sure it is delivering enough water, isn’t clogged and isn't over watering – all problems that come with age in drip irrigation systems. If an emitter is delivering much more or much less water than others on the line, it can change the system pressure and affect the other emitters. The simple solution is to replace it.

Plants in pots will require more frequent watering than those in the ground. As the soil dries, it pulls away from the sides of the pots, allowing water to run through the soil without penetrating the soil. Sun shining on the pot, whether black plastic or clay, will steam the roots of the plant which also requires more water to maintain a cooler temperature of the soil. Despite this issue, plastic is still preferred over clay as clay loses moisture through the porous nature of it. If possible, double potting would help maintain better control. This practice would at least have a curtain of cooling air between the pots, and an insulation of some type would be more efficient. One more thing, the longer the soil is in a pot, the less porous space is available in the root zone – so repot every two years or so.

This time of year with hot temps also attracts spider mites. This topic was covered in a previous care column which you can find on the www.TemeculaValleyRoseSociety.org newsletter; look for “Care for September 2013.” If you see signs of yellowing foliage you may have an infestation. Check the underside of the lower leaves for grainy feeling substance or tap onto a paper to see these very small critters. The easiest way to treat is to use fairly strong spray of water from below to give the plant a shower and rinse them to the ground. If you see fine webbing, you may need a stronger method.

I’ve also noticed that another problem as result of the weather has appeared this year. The high temps and humidity have increased instances of Black Spot, indicated by yellow leaves with usually round shaped black spots. With the humidity comes dewy nights which then tends to incubate powdery mildew.

Now would be another good time to order composted mulch. Here is a formula you can use to determine the quantity you will need. An area 10 feet by 50 feet needs 4-5 cubic yards to cover the garden 3-4 inches deep, which I recommend. This mulch is the best product you can apply to protect your roses roots from heat and cold.

A valuable bimonthly magazine which covers rose topics is the “American Rose” published by the American Rose Society. Go to www.ARS.org for more information on obtaining it.

When you have a moment to spare or feel the need to get away or when the day cools down, take your favorite beverage, a picnic basket and visit our local one-of-a-kind Rose Haven Heritage Garden, 30592 Jedediah Smith Road, in Temecula at the cross street, Cabrillo Avenue. Also, visit our website, www.TemeculaValleyRoseSociety.org.