By Frank Brines
ARS Master Consulting Rosarian 

How to plan for rose blooms

 

Last updated 9/13/2019 at 10:30pm

As I look back over my previous articles, I noticed that since 2013 it seems there is what I suggest is a new normal of high temperatures for August-September. The average day-night temperatures in the first 25 days of August 2018 were higher than nearly every day in August 2017. The average daytime high for August 2019 was 1.6 degrees cooler than for 2018, the average nighttime temperature for 2019 was 4 degrees cooler than for 2018.

I checked the weather projections and learned that temperatures for the next 7-10 days for Southern California are for low 90s, cooler than the 100-plus predicted for the same period in September 2017. Add to that higher than normal humidity due to warmer ocean temperatures at local beaches. All in all temperatures are trending higher in the last five years.

If any gardeners are participating in my prescribed practice of allowing a summer of rest for roses, it will be several weeks still until the midseason pruning. As a wise man once said, “Predicting things is difficult, especially in the future,” but I can only assume it will look a little like the past, especially with the weather. So I’ll give it a try.


This year I’m starting to do my midseason pruning Sept. 1, in hopes of having blossoms for fall rose society shows. If someone has a special event for which they would like to have fresh rose blooms, count back 6-8 weeks from that planned event to determine when to do that end-of-summer pruning.

Roses could possibly have two more bloom cycles this calendar year. Remember, a midseason 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 leaf with five leaflets.

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 be severely damaged or killed. Assess conditions every morning. Look for wilted or dry crisping foliage. Sometimes if it is discovered 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 that inspection doesn’t happen until the afternoon or evening, it may be too late or the inspection might not give a good assessment of the plant’s condition. After a hot day, most plants can appear wilted while still receiving sufficient hydration. Also inspect the 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 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 to consider: 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 temperatures also attract spider mites. This topic was covered in a previous care column which can be found on the http://www.TemeculaValleyRoseSociety.org newsletter; look for Care for September 2013. The signs of yellowing foliage may indicate an infestation. Check the underside of the lower leaves for grainy feeling substance or tap onto a paper to see these tiny critters. The easiest way to treat for spider mites is to use strong spray of water from below to give the plant a shower and rinse the mites to the ground. If fine webbing is seen, it 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 as 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. I have been troubled by this mildew throughout this year in my garden. To date I have not discovered damage from chili thrips; however that is difficult to recognize until it becomes obvious. At the first signs of any of these pests, it is best to start treating with a fungicide or pesticide, preferably one containing Spinosad.

After the pruning has been accomplished and after at least one thorough application of water, apply a good fertilizer. Read the directions on the container to discern type of application and what to do. I use granules, powder or liquid and water it in for the quickest effect. My colleagues are recommending the use of fish emulsion and seaweed fertilizers at the rate of 1 tablespoon each per gallon of water applied now. Remember to never fertilize a dry or stressed plant – always water the day before.

Now would be a good time to order composted mulch. Here is a formula to use to determine the quantity needed. An area 10-feet by 50-feet needs 4-5 cubic yards to cover the garden 3-4 inches deep which what I recommend. Mulch is the best product to apply to protect 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 http://www.ARS.org for more information on obtaining it.

When there’s a moment to spare or when the day cools down, take a favorite beverage, a picnic basket and visit the Rose Haven Heritage Garden, 30592 Jedediah Smith Road, in Temecula. The cross street is Cabrillo Avenue. Also, visit http://www.TemeculaValleyRoseSociety.org. Spread the joy of roses.

 

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