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How to care for roses in higher temps

Frank Brines

ARS Master Rosarian

I checked the weather projections and learned that temperatures in the Temecula Valley for the first week of September are in the mid-80s. The higher-than-normal humidity (due to warmer ocean water temperatures) will make it feel warmer. All in all, temperatures are trending higher in the last five years.

The deluge from Tropical Storm Hilary will help recharge our soils, but please stay alert to the water status of your roses as the month progresses, and continue to do so until cooler weather.

If you're using drip irrigation, run your system in the early evening to give your roses the opportunity to thoroughly hydrate overnight. If you're using a hose or other non-surface method, do it in the early morning – it's best to avoid getting water on vegetation during hot sunny days.

It takes only a few days in these temperatures without sufficient water for a bush to be severely damaged or killed. Assess conditions every morning. 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. Look for wilted or dry crisping foliage. Sometimes if you discover it soon enough, dousing the stems and leaves with plenty of water in addition to applying plenty of water to the ground, may save the plant.

If you have critters, give the wilted plant just enough tug to see if the roots may have been eaten. If the plant comes up, put it in a bucket of water or bury the part left in the ground. Give it lots of water and hope it survives

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: Replace it.

Plants in pots 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) can steam the roots of the plant which also requires more water to maintain a cooler temperature of the soil. This being said, plastic is still preferred over clay as clay loses moisture through its many pores.

Double potting can moderate drying. This practice would at least have a curtain of cooling air between the pots, 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, the hot temps can attract spider mites. If you see signs of yellowing foliage you may have an infestation. Check the underside of the lower leaves for a grainy feeling substance or tap onto a paper to see these very small critters. The easiest way to treat it is to use a strong spray of water from below then give the plant a shower and rinse the mites to the ground. If you see fine webbing you may need a stronger method.

I've noticed another problem as a result of the weather this year: High temps and humidity have increased instances of Black Spot (indicated by yellow leaves with usually round-shaped black spots). I have not seen any sign of Black Spot in my garden yet. With the humidity comes dewy nights which then tends to incubate powdery mildew. At the first signs of any disease, it is best to start treating with a fungicide or a pesticide (preferably one containing Spinosad).

If you're following my prescribed practice of allowing your roses to rest during the summer, 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 the future," but one can only assume it will look a little like the past, especially with the weather. This year I plan to do my mid-season pruning in mid-September as preparation for fall rose shows.

If you have a special event for which you would like to have fresh rose blooms, count back 6-8 weeks from that planned event to determine when you should do your end-of-summer pruning. You can possibly have two more bloom cycles this calendar year.

Remember, mid-season pruning is light, removing any point along a cane where many stems of blooms came out. For quicker repeat blooming, prune each cane back to just above the outward-facing bud at the base of the first five leaflets.

After the pruning has been accomplished and at least one thorough application of water, apply a good fertilizer. Read the directions on the container to discern the type of application and what to do. I use granules, powder or liquid and water it in for the quickest effect.

I recommend the use of fish emulsion and seaweed fertilizers with phosphate at the rate of 1Tbs each per gallon of water applied now. Two gallons for larger types and one gallon for smaller types. Remember: Never fertilize a dry or stressed plant - always water the day before.

Now is a great time to clear the debris in, around, and under your rose garden. Due to the heat, you may have a lot of leaf drop and old petals build up. Keeping the garden free of debris all year is best practice. Once that's done, it's a good time to apply composted mulch. An area 10' x 50' needs 4-5 cubic yards to cover the garden 3"- 4" (which is the depth I recommend). This is the best product you can apply to protect your roses roots from heat and cold.

A valuable bi-monthly magazine that covers rose topics is the "American Rose" published by the American Rose Society (ARS). Go to http://www.ARS.org or rose.org for more information on obtaining it.

When you have a moment to spare visit our website, http://www.TemeculaValleyRoseSociety.org.

 

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