Type your question here!

Tuesday, August 11, 2015

Rose Primer for the Desert

Hybrid Tea rose  'Las Vegas'
Q. I enjoy your page in the RJ, but I cannot see that you ever write about ROSE BUSHES.  We inherited these 14 year old, (estimate), bushes when we bought this house in 2011.  I ask friends, that have roses, and up until this summer, used Lady Bugs, Rose food, have hosed out salts from the roots, etc.  The bushes take up one side of the front of my walk way, plus in 3 other places, and it is important to me, that they look nice.Thank you for your thoughts on my problem.

A. Thanks for asking that question. I seldom generate my own questions so I rely on the public to send these questions to me. It is my hope that people who read my blog and newspaper article will ask questions that many other people are also asking themselves. I seldom try to "second-guess" what people are thinking. Let's cover some general tips on roses and this would be posted on my blog and an abbreviated form of it in my gardening column.

There are two Rose Societies in the Las Vegas Valley; the long-standing Las Vegas Valley Rose Society and a second one which split from the original as the Las Vegas valley became larger, South Valley Rose Society

Get information about the Las Vegas Rose Society
Go to the South Valley Rose Society website

I consider many of these members to be outstanding Rosarians and I defer to them and their expertise. However, I will give you my version of growing roses here in the eastern Mojave Desert.

Roses do extremely well in our climate. The "winter" for roses is during the heat of the summer; June July and August. Expect that roses will look their worst in these months. The rest of the year
Rosa canina, dog rose, used in Central Asia for its high Vitamin C content
they do beautifully and are very prolific bloomers. If you want your roses to bloom during late December and January, plant them close to a south facing wall that throws radiant heat out during the winter.

Our garden rose takes many different forms from miniatures to climbing roses to the garden rose in its many forms such as the Hybrid Teas, Floribundas, Grandiflora and the so-called shrub roses. Shrub roses is a catchall category for those that don't fit anything else. All of them will grow in our climate but an excellent grower and hybridizer of roses, 

puts together a list of roses that do well in our desert climate and publishes it every year 

If you are planning to grow roses, I would strongly suggest that you pay very close attention to your Rose selection by following lists such as these. These are solid recommendations.
Rose 'Nevada' a semi-doubled shrub rose developed in 1927. 

Blah, Blah, Blah. Most of the roses that are popular among home gardeners are what we call "repeat bloomers". Roses weren't always like this. Roses grew in different places all over the world including the Americas but the ancestors of what we now recognize as a modern garden rose had its origins most likely in western China and Central Asia. These areas of the world are very dry. International traders like Marco Polo, before and after him, moved these roses all over the world including the Middle East, northern Africa Eastern Europe and Western Europe. 

Before and after these roses were moved internationally, horticulturists and gardeners began to breed them for different traits. The two traits that probably dominated most of the breeding early on was flower color and repeat blooming. Once the repeat bloomer discovered in China was identified, there was a scramble by many ancient Rose enthusiasts to "breed" this trait into the garden rose. VoilĂ . All of our popular garden roses now are repeat bloomers. Other traits popular were oil production and floral aroma which is tied very closely to the type of oils produced.

Marco Polo trade routes from China
Moving roses from dry Central Asia and western China to the wetter climates of Europe produced an increased number of disease and insect problems. We can see the reverse of this when we grow roses in desert climates. We see disease and insect problems are normally minimal so the need for spraying roses in our climate because of diseases and insects is small.
Aphids on unopened rose flower buds

Selection of roses for the home garden. Use a list like the one I talked about earlier to pick a variety that does best in our desert climate. Nearly all other varieties will do well but growing those selected for the desert that will tolerate the heat and our soils will do better than others.

Straight phosphorus

Planting roses. If you plant into native desert soil, blend this soil with an equal amount of good quality compost. If you are using a good quality soil mix, plant directly into this mix without amending the soil. Add a starter fertilizer high in phosphorus mixed into the backfill surrounding the roots at the time of planting.

Always plant into a "wet" hole, never plant directly into dry soil or a dry soil mix.

Wood chip mulch, not bark mulch, for soil improvement
Always cover the surface of the soil with 3 to 4 inches of mulch that decomposes adding organic matter to the soil as it does. This type of mulch is a "wood chip mulch", not a bark mulch or a rock mulch. If you must use a bark mulch, then use a wood chip mulch first and cover the surface last with bark mulch.
Fertilizers. When first planting roses use a fertilizer high in phosphorus blended into the backfill at the time of planting. Or just use a straight phosphorus fertilizer instead. Once planted, focus on getting some size on the plant by using fertilizers high in nitrogen.
Good high phosphorus fertilizer for roses

Applying a fertilizer once a year in January is sufficient but if you really want roses that "show off" then fertilize more often with a smaller amount of fertilizer each time. Once the rose has established some size in the second or third year of growth, it is ready to start a regular fertilizer schedule focused on flower production. 

Put your first fertilizer application on the soil in January along with a good iron fertilizer such as iron chelate as EDDHA. If you apply iron to the soil, only one application of iron is needed. Apply a fertilizer the second time in April before it gets hot. Avoid fertilizing roses during the heat of the summer.
As the temperatures begin to cool, in mid-September  to early October, make a third application of fertilizer. Just before cold weather sets in, make your fourth application around Thanksgiving. Once roses are mature enough to begin heavy flower production, focus your fertilizers on moderate levels to low levels of nitrogen (the first number) and moderate to high levels of phosphorus (the second number). Always keep your potassium levels moderate to high (third number).

Foliar fertilizer for flowering
You can always substitute foliar applications of a good fertilizer instead of applying it to the soil but this requires more equipment and effort on your part. Foliar applications to roses can be a problem at times because of damage to the flowers.

Some people like to apply Epsom salts to roses. That is a personal choice and there are claims about the value of Epsom salts to roses by many Rosarians.

Irrigation. Roses do extremely well with drip irrigation and wood chip mulch. Use two emitters per plant, one on either side of the plant about 6 to 12 inches away from its center depending on the size of the rose. Once roses are established, water them 2 to 3 times a week during the heat of the summer provided you have the soil covered with wood chip mulch. They will probably need water more often if you don't. 

As temperatures cool in the spring and fall months, water less often but with the same number of minutes for each irrigation. During the winter you may be applying water only once every seven days to two weeks depending on whether your rose is producing flowers or has gone dormant for the winter.

Drip emitter for precise irrigation
The number of minutes to water depends on the other plants on the same irrigation valve. Note the number of minutes you are currently using and select a drip emitters size that will give you 2 to 3 gallons from each emitter during those minutes.

An example: you are planting roses that will use water from an irrigation line which delivers water for 30 total minutes in that irrigation cycle. Answer: Two, 5 gallon per hour drip emitters will deliver a total of 5 gallons in 30 minutes. You would use two, 5 gallon emitters.

Example 2: you are planting roses that will use water from an irrigation line which delivers water for 20 total minutes in an irrigation cycle. Answer: use three emitters. Three, 4 gallon per hour emitters will deliver 4 gallons in 20 minutes. Use three, 4 gallon per hour emitters.

Powdery mildew of rose
Pruning. Major pruning is done in late December to early January. Light pruning can be done at any time. Light pruning is removal of new growth only, such as suckers and growth which is vertical.

Another form of pruning is deadheading. Deadheading is removing old, spent flowers when they are no longer pretty. This will help to encourage more flowers and improves the look of the plants. Remove these flowers at any time they are finished.

Insects and diseases. As I said earlier, insects and diseases are not very common in our desert climate. However, they do occur. Insects to be on the lookout for include aphids, flower thrips, spider mites, leaf cutter bee and cane borer. Japanese beetle has never been reported in southern Nevada and, to my knowledge, mossy gall wasp has not as well.

Iron chlorosis on apricot but shows green veins and yellow
Diseases from disease organisms are infrequent but occasionally occur when overhead irrigation is used (spraying the foliage with water), roses are planted in areas where there is excessive shade or very poor air movement. 

The most common disease is powdery mildew. This can be controlled by selecting a variety that is less susceptible to powdery mildew (another reason to use the list I mentioned earlier) and the crown gall. Other diseases of roses such as black spot, botrytis, winter cold damage or canker are hardly ever, if ever, a problem. 

Problems not caused by disease organisms include iron chlorosis, wind damage and root rots that cause dieback or death from watering too often or poor soil drainage.

When buying roses, make an investment. By a good quality rose right at the start.

1 comment:

  1. Superb reply about roses. I hope you do not mind my adding:
    The Rose in the Desert Southwest - University of Nevada

    http://cals.arizona.edu/maricopa/garden/html/pubs/pubs.htm#Flowers - Arizona link to 3 articles on roses in the low desert (a 4th missing one az1306 was withdrawn when az1528 was published due to extreme redundancy).