Rose care tips for November

Frank Brines, ARS Rosarian

Special to the Village News

The weather has moderated slightly, and along with the change comes cooler nights. Fall brings warm days and cool nights, conditions that can ensure large colorful blossoms. But those same conditions also bring moisture and a daily accumulation of ash and small dust particles. These create a great environment for fungal diseases. One example is powdery mildew. Early on, it shows slight purple splotches on the underside of leaves and white powdery spots on top and white powder on the peduncle or neck of the rose blossom.

Another common fungal disease is black spot. It is marked by black spots with fuzzy edges, before turning yellow and brown. Often it does not 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 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 will appear as rot of blossoms and will usually prevent them from opening. Another sign is red blotches on blooms. I included an article about chilli thrips and pictures for identifying the problem they cause in the September care column: https://www.temeculavalleyrosesociety.org/nl/NL202109.shtml#h12.

Continue to investigate the plants for these pests and treat them if found. The pests 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.

If you completed the light mid-season pruning in September to October as suggested in an earlier article, you pruned out dead, crossing canes and thinned the middle of the plant. This action will improve air circulation through the bush and reduce possible fungal diseases. This mid-season pruning and fertilizing encourages a new blooming cycle. Feel free to cut some of the early blooms now and take them inside for bouquets.

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 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 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 (e.g., cold at this time of year); 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.

I do not recommend doing the winter pruning before January. 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. Be sure to keep them hydrated for best results. The weather forecast for the next week is around the mid-80s.The cooler temperatures can be misleading. Roses still need to be watered, perhaps not as often.

With climate change and presence of pests and fungi, I have had to use an integrated pest management program. Being completely organic is becoming harder and harder. IPM is a program which allows one to begin with the lesser of toxic treatments which hopefully will manage the problem.

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 our magically misty fall. When you have a moment to spare, or feel the need to get away, or when the day cools down, take your 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, both printed and online, for that next "gotta have" rose variety.

The September/October America's Rose Garden issue has a good section on some new or recent roses and Bob Martin's annual compilation of the newest roses. 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 your 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.