By Frank Brines
ARS Master Consulting Rosarian 

How to care for rose bushes in November

 

Last updated 11/7/2019 at 5:25am



After experiencing a summer of high temperatures and currently fires, smoke, ash and Santa Ana winds, gardeners look forward to having some relief. The weather has moderated slightly, and along with the change comes cooler nights with more moisture collecting on leaves. This moisture with the daily accumulation of ash and small dust particles provides a great environment for mildew, rust and black spot on roses.

Black spot is the most common and important disease of roses and can be found everywhere roses grow. The disease 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.

A potential “lookalike” disease is spot anthracnose or shot-hole disease; it is not a major problem unless temperatures are very hot, that is, too hot for black spot. Spots caused by black spot are fuzzy around the edges, then turn yellow and brown.


Spots caused by anthracnose are smooth edged and the centers turn gray and drop out. The treatment is the same, but if a fungicide is used, it must be labeled for black spot or anthracnose, whichever disease is being treated.

Fall brings warm days, cool nights, increased moisture and air dust particles. These conditions will ensure large colorful blossoms and the possibility of powdery mildew. One of the earliest signs will be 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. A good fungicide will be needed and applied at the first sight of white appearing substance on the leaves.

Fall is a good time to check the pH of the soil. It should be between 6.0 and 6.5. Any reading below or above these levels will inhibit roses’ ability to use the nutrients in any fertilizer or soil amendement. Treating the pH problem now will give ample time for adjustments before spring pruning. The most likely result will be a low pH due to the acidifying effect of fertilizers.

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.

In October, I included information about chilli thrips and pictures for identifying the problem they cause. Continue treatments for these micro pests. 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 includes them falling to the ground and becoming a grub and reappearing when temperatures warm up next year.

If gardeners completed the light midseason pruning in September or October as suggested in an earlier article, they pruned out dead, crossing canes and thinned the middle of the plant. This pruning will improve air circulation through the bush and reduce possible fungal diseases.

The midseason pruning and fertilizing encourages a new blooming cycle. Feel free to cut some of early blooms now and take them inside for bouquets.

Gardeners may make a final application of fertilizer for the year before mid-November. Unless they plan to exhibit, I do not recommend fertilizing after mid-October. If a gardener chooses to do it, use a fertilizer lower in nitrogen and higher in phosphate and potassium (K); that is, if the 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 or ask a professional nursery person for guidance.

To explain: nitrogen encourages foliage growth – something gardeners will 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 at this time of year; potassium is a helper of phosphate and aids in bloom quality.



If a gardener applies 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.

Remember to check the garden daily for any changes. Be sure to keep plants hydrated for best results. The cooler temperatures can be misleading. Roses still need to be watered, perhaps not as often.

Some people think Southern California lacks distinct seasons, but it does 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 weather.

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. For other venues that are available this time of year and may be of interest, check out http://pswdroses.org/calendat.html.

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 other suggestions as where to look for more. 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 a gardener plans to replace an old tired plant, prepare the area now for easier planting later.

For more ideas, visit Rose Haven Heritage Garden, 30592 Jedediah Smith Road, in Temecula. The cross street is Cabrillo Avenue. Also, visit http://www.TemeculaValleyRoseSociety.org/index.html.

 

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