RHA Newsletter 5(2): 9-11 (Summer 1974)
WINTER HARDY AND DISEASE RESISTANT ROSES
by Don Nielson

The rose growers who live in the desert and semi-desert 1/3 of the United States learned many years ago that the best winter protection for the popular commercial roses, was management. 95-100% of the water used by the growing plant must be supplied by the grower. These management practices include:

  1. Plant the bush deep enough to protect the graft union from the zero to 40° below zero winter temperatures. This means 3 to 4 inches below the ground surface.
  2. Do not use nitrogen fertilizer after July 1st, each year except in such places as Phoenix, Arizona, El Paso, Texas and Las Cruces, New Mexico, where the growing season may last until Christmas.
  3. Limit the removal of blooms after the first frost to a few for the house.
  4. Stop the irrigation at the first frost to allow drouthing and to force the bush into conditions which allow it to go through the cold part of the winter with minimum damage to the canes.

In this area the only disease is mildew. When I decided to orient my rose breeding program to winter hardiness and disease resistance, I found that I did not have any information on which cultivars were winter hardy. All cultivars survived the desert winter conditions in very good condition. Several cultivars requiring weekly spraying to control mildew did lose the late canes during the coldest winters.

With this clue I decided to force rapid growth up to the time the temperature dropped to 12 degrees for at least one night by irrigating each week, removing all blooms and using nitrogen in late August.

This procedure was followed for the winters beginning in the fall 1971, 1972 and 1973. Cane breaks were numerous each year. Most made 4 feet of growth and a few made 7 feet of growth after I would normally have started preparing the bushes for winter.

During the winter of 1971-1972 the temperature dropped to 14 below during Christmas week. There was 3 inches of settled snow at that time. Warm temperatures (40 to 50 day time) came in February for 6 weeks then we received a series of night time temperatures of 14 to 30 degrees above zero which occurred every 4th night until June 1st.

For the winter of 1972-1973 there was no snow. On Dec. 20th the temperature dropped to 17 below zero and did not get above zero for 45 days. The ground was frozen to a depth of more than 2 feet. Most canes split open at the ground surface. A few split full length of the canes.

In 1973-1974 we received the first precipitation in 18 months beginning about November 1st. This continued to include 8 inches of settled snow on Jan. 1st. Temperatures varied from 12 above zero to 10 below until Jan. 15th. A chinook wind raised the temperature to 50 degrees and we had summer until April 1st, when it dropped to 20 above. Only a few nights with temperatures at freezing or just barely below have occurred since January 15th.

RESULTS

  1. No damage to leaves or canes at 10 below zero: A 1973 Jackson & Perkins trial rose, Three seedlings, Kordes Perfecta.
  2. Some leaves killed. No damage to canes: Antigua, Apollo.
  3. All leaves killed. No damage to canes: Heirloom, Irish Gold.
  4. Leaves killed, some canes killed, some canes undamaged: Saratoga, McGredy's Ivory
  5. Leaves killed, top 12-18" of canes killed: Peace, Command Performance, Miss All-American Beauty, Medallion, Snow Fire, Golden Masterpiece, Old Timer, White Masterpiece, Sutter's Gold, Arctic Flame.
  6. Leaves killed, late canes killed, others undamaged: Peach Glow.
  7. Canes killed to snowline: Command Performance, Medallion, Valencia, Sterling Silver, Don Juan, Will Rogers, Sierra Dawn, Tropicana, Lily Pons, Shades of Autumn
  8. Some canes killed to snowline, others to pound surface.: Queen Elizabeth, Angel Face, Miss All American Beauty, Mirandy, Red Masterpiece, Chicago Peace, Jadis.
  9. All canes killed to ground surface: Electron, Mr. Lincoln, Karl Herbst, San Diego, Allegro, Pink Peace, Contessa de Sastago, Red Chief, Summer Sunshine, Lemon Spice, Golden Gate.
  10. Bush killed at 17 below, no snow, ground frozen to 2 or more feet below ground surface: Sterling Silver, Old Timer, Mr. Lincoln, Summer Sunshine, Lemon Spice, Golden Gate, Fragrant Cloud. Golden Jubilee and Eclipse.

COMMENTS:

The roses which died under the most extreme conditions of the study period require the most intensive spray program to control mildew. The roses which had little or no winter damage during the study needed only 3 spray applications each year to control mildew. One seedling with no damage had no mildew and was not sprayed for mildew. The other 2 seedlings with no winter damage had no mildew but received 3 spray applications, one of Karathane and 2 of Benlate each year.

Of the 27 seedlings I have kept for my breeding program, 2 are interesting as potential trial garden entries; the rest are not trial garden possibilities, below because of minor deficiencies in the bush, stem or bloom. When Heirloom and Arctic Flame had 1 inch of growth the temperature dropped to 20 degrees. About, 3 out of 4 shoots were damaged and after more than 3 weeks, less than half of the shoots are beginning to grow again. About 1/4 of the shoots are dead. This did not happen to any other cultivar. Bushes which have established their own roots made more rapid recovery than those which must use the root to which it was grafted. The own root plants still have the root below the graft.

CONCLUSIONS:

Hybrid teas, floribundas and climbing roses which have little or no leaf kill at below zero temperatures will be most resistant to disease and will have the least damage from cold weather with or without wet feet under my conditions.

Resistance to disease and winter hardiness may be tied together in the chromosome or gene makeup.

If the cultivated rose as we know it could be combined with a species rose which is disease resistant, and drops its leaves when the temperature reaches 12 to 20 degrees above zero, we may get disease resistant roses for the world and roses which need no protection except management for the colder parts of the United States including Alaska, and Canada.

The use of species roses native to northern United States in a breeding program may give the desired results. I will use the roses named in items 1-5 in my program, even though 3 years is too short for guaranteed results.