Rose Care FUNdamentals for November 2023

Frank Brines, ARS Master Rosarian

Special to Village News

The projected temperature for the first week of November 2023 is near the historical average of mid-70s.

If November temperatures turn hot again, chilli thrips may continue to be a problem. Continue to investigate for these pests and treat them if found. They attack new growth, buds and blooms. Left untreated plants are stressed greatly, often shriveling the end buds or preventing bud formation.

The life cycle of chilli thrips is short and includes falling to ground and becoming a grub and reappearing when warm weather arrives. One application of a pesticide spray is not sufficient for control. Follow the prescribed frequency on the product directions. Treat with an insecticide that contains spinosad.

Fall brings warm days and cool nights; conditions that can ensure large colorful blossoms. But those same conditions can also bring moisture and a daily accumulation of ash and small dust particles. The buildup creates an environment for fungal diseases such as powdery mildew. Early on, it shows up as slight purple splotches on the underside of leaves and white powdery spots on top and white powder on the neck of the rose blossom.

Another common fungal disease is black spot. It is marked by black spots with fuzzy edges that then turn yellow and brown. Often it doesn't kill the plant outright, but, over time, the loss of leaves can weaken the plant, making it more susceptible to other stresses and to winter damage. It first develops on upper leaf surfaces, later adjacent areas turn yellow and leaves drop prematurely, usually beginning at the bottom of the plant progressing upward.

Yet another disease that presents similar signs is anthracnose. It produces dark spots that are smooth edged with centers that turn gray and drop out. Treatment is the same for all three diseases: fungicide. If you’re unsure which disease your roses are battling, just be sure the product is labeled for all three.

Roses benefit from a good rinsing to remove accumulated dust: Be sure to keep moisture off the blossoms to prevent yet another fungal disease, botrytis, which first appears as red blotches on blooms and can progress to blossom rot that usually prevents them from opening. Best treatment is to cut, bag and dispose of it immediately.

If you completed the light mid-season pruning in September/October as suggested in an earlier article, you pruned out dead, crossing canes and thinned the middle of the plant. It will improve air circulation through the bush and reduce possible fungal diseases. That pruning and fertilizing encourages a new blooming cycle. Feel free to cut some early blooms now and take them inside for bouquets. Remember to clean/sterilize pruners between moving from one bush to another to prevent transferring disease organisms.

Fall is a good time to check the pH of the soil. It should be slightly acidic, between 6.0 and 6.5. Any reading significantly below or above these levels will inhibit roses ability to use the nutrients you are giving them. Treating the pH problem now will give ample time for adjustments before spring pruning.

Unless you plan to exhibit, I do not recommend fertilizing after mid-October, but if you really feel that you must, you may make a final application of fertilizer for the year before mid-November. If you do this, use a fertilizer lower in nitrogen (N) and higher in phosphate (P) and potassium (K); that is, if your fertilizer has an N-P-K number on it, the first digit will be lower than the other two. If it lacks an N-P-K, read the ingredients and/or ask your professional nursery person for guidance. To explain, nitrogen encourages foliage growth-something we want to discourage as the plants go into their winter dormancy; phosphate helps build root structure and resistance to stressful conditions, such as the cold temperatures at this time of year and potassium is a helper of phosphate and aids in bloom quality. If you use an organic fertilizer it will be readily available when the soil warms, adding to the nutrients needed for that Spring growth spurt. A liquid fertilizer as the last application will be readily available.

In the Temecula Valley, I do not recommend doing the winter pruning before February. It is possible to have roses for Christmas in Southern California so why make the season more hectic with another activity?

Remember to check your garden daily for any changes. Keep roses hydrated but not soggy for best results. The weather forecast for the next two weeks is generally around the low to mid 70s, but cooler temperatures can be misleading: Roses still need to be watered, but perhaps not as often.

I try to adhere to a program of integrated pest management. With the wide range of pests invading the region, as well as their increased resistance to long-used treatments, being completely organic is becoming harder and harder. Integrated pest management attempts to make the softest impact on the natural environment, relying on “natural” methods – rinsing, air circulation, beneficial insects, etc. – as well as on less toxic treatments to manage pests and diseases.

Some people think Southern California lacks distinct seasons, but we do have seasons. They are only discerned by those with a more sophisticated palette. So get out of the house and enjoy the subtle delights of the air, sun and the rich aroma of the magically misty fall. When you have a moment to spare, feel the need to get away or when the day cools down, take a favorite healthy beverage and a picnic basket and visit Rose Haven Heritage Garden, 30592 Jedediah Smith Road, in Temecula. The cross street is Cabrillo Avenue. The early morning and late afternoon sunlight across the pass is magical this time of year – it even makes the freeway seem a little bit romantic.

Oh, one last thing – something to do when it gets just a bit too nippy out there. Start perusing rose catalogs – printed and online – for that next “gotta have” rose variety. The 2022 September/October America’s Rose Garden issue has a good section on some new or recent roses and is full of other rose information. Also, this time of year many nurseries and garden stores are liquidating their remaining inventory of potted roses, and you’re in luck because November is an ideal time to purchase and plant. Make a list of new roses and go shopping. If you plan to replace an old tired plant, prepare the area now for easier planting later. And assess your stock of fertilizers and be sure to order next month from the San Diego Rose Society.

For more ideas, visit http://TemeculaValleyRoseSociety.org/index.html.