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Posts Tagged ‘Roses’

Durango, Colorado

Irvine, California

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Durango, Colorado

Irvine, California

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Durango, Colorado

Irvine, California

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How annoying is powdery mildew? Very! It always seems that the minute we have every other pest and scourge finally under control, back comes the powdery mildew. Unless you have a really extensive outbreak, it’s relatively harmless, but make sure  you take action at the first sign of it. If you don’t you’ll have some ugly deformed plants and a severe case will kill them.

As for the conditions that promote powdery mildew, here’s a passage from the Perdue University Department of Botany web page: “High relative humidity at night and low relative humidity during the day with temperatures of 70 – 80F (conditions that prevail in spring and fall) favor powdery mildew. Maintaining conditions that favor rapid drying of foliage will help reduce disease incidence. Locate susceptible plants in open areas where they will not be crowded. Plants in shade are more prone to mildew than are those growing in sunlight. Prune to thin out any dense foliage; this will increase air movement and favor rapid drying of foliage. Avoid nightly sprinkling during August and September; instead, soak the soil as needed.”

Organically grown plants tend to be much more resistant to fungus diseases than those grow with synthetic chemicals and fertilizers because the soil they are planted in is full of beneficial fungi that counteract the harmful stuff. However, excessive nitrogen will promote lush, tender green growth that is very susceptible to powdery mildew, so this late in the season use a more balanced fertilizer on your plants.

There are lots of organic treatments for powdery mildew. You can buy commercially prepared products of which there are many — look for the OMRI (Organic Materials Review Institute) label, or you can mix your own.

A very simple treatment can be mixed using 1 oz. of milk to 9 oz. of water. Spray at the first signs of mildew and every week after for about 3 – 4 weeks. You can keep spraying as a preventative weekly if you like.

Another remedy suggested in the  Sunset Western Garden book uses garlic: mix 3 oz. of minced garlic with 1 oz. of vegetable  oil and let soak for 24 hours. Strain, stir in 1 tablespoon of liquid castile soap and store in a sealed container. It will keep at room temperature for several months. To use, mix 2 tablespoons of the garlic mixture in 1 pint of water. Spray every week for 3 – 4 weeks.

These treatments can be used on ornamental plants and food crops, though I would wash any edibles before eating.

If you notice that particular plants get a bad case of powdery mildew it might be time to consider replacing them with something that is more resistant.

For instance this rose — Brass Band I think — always had a bad case of mildew, which is a sign that it’s not suited to the conditions in my yard or area. I’m close enough to the ocean to be affected by the marine layer that creeps in every night carrying a lot of moisture with it. It’s out of here next year, to be replaced by a rose that is more resistant.

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Block Island, Rhode Island

Irvine, California

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Block Island, Rhode Island

Irvine, California


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Last week our tips focused on pruning hybrid tea and floribunda roses in coastal Southern California. Today we’ll finish up with tips for pruning Old Garden Roses, shrub roses, standard or tree roses, and climbers. Don’t forget to clean and sharpen your tools before you start —  a clean cut is important.

Let’s start with standard or tree roses. If I’d had any sense I would have included this category in last week’s post because the most common type is a hybrid tea or a floribunda grafted on top of a long cane. Growers take a rootstock like Dr. Huey (the rootstock most commonly used on grafted roses) with one strong, straight cane and graft a another rose on top of it.

Prune standards just like you would a regular rose of its type. For a standard that’s been grafted with a hybrid tea, remove the leaves, choose 3 -5 of the strongest canes to keep, prune out crossing, old or diseased canes, and spindly, twiggy growth, always cutting just above an outward-facing budeye. You want to open up the middle and create a vase shape, but keep an eye on the overall shape of the head; it should be rounded. Don’t cut back more than one-third to one-half of the top growth. Whatever you do don’t cut below the graft point except to remove any shoots or suckers growing from the main stem near the ground.

Remove (clip off) leaves, clean up under the plants, and spray with a dormant spray.

Old Garden Roses include Gallica, Damask, Moss, Alba, and Centifolia roses. These roses bloom one time in the spring so they should be pruned right after the bloom period, usually early summer, and not in the winter. Repeat bloomers like Portland, Bourbon, Hybrid Perpetual, Perpetual Damask, and Perpetual Moss should be pruned as you would a hybrid tea.

Shrub roses and species roses should be lightly pruned by shortening flowering shoots a few inches. Remove any diseased, damaged, or dead canes.

Climbers are a different story altogether because of how they grow and flower. Climbing roses produce growth hormones in their growing tips. This hormone will inhibit flower formation along the cane unless the tip is horizontal, in which case the cane will flower at each budeye along the cane. So instead of just a cluster of blooms at the tip of an upright cane, a cane that’s been trained into a horizontal position, will produce many, many blossoms.

The goal in pruning climbers is to create a symmetrical shape and to force a dormant period which renews the plants and brings more flowers in the spring. If your climber is young, you may not need to do much, if any, pruning at all. Let it grow and become established, but if some of the growth is very spindly and weak, shorten or remove it.

For established climbers remove spindly, twiggy growth, remove any leafless shoots, and prune out any dead, damaged or diseased growth. Tip prune to the first outer facing bud to encourage lateral growth. I have climbers that are tied to a fence and sometimes a cane or a sucker will grow straight out at a right angle. I take these off at the point of origin throughout the year.

Remove (clip off) all the leaves, clean up under and around the plants and spray with dormant spray to get rid of overwintering pests and diseases. Be sure to spray in the early morning or late afternoon when the bees and other beneficials won’t be affected.

Wait to fertilize until you see the first new growth in the spring (usually in March).

P.S. Don’t prune Lady Banks roses now! These roses (and some other varieties) bloom once in the spring. If you do prune them now, you won’t get any blossoms this year. I learned this the hard way.

If you have a type of rose that isn’t mentioned in this or last week’s post, or if you’re unsure of what you have, ask your local nursery for advice.

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