Rose Rosette Disease

A couple of weeks ago, I gave a talk to a garden club in Fayetteville. After the talk, a woman came up to me with a piece of a rose in a plastic bag, and asked me what caused the problem. It was rose rosette disease. Unfortunately, this is something gardeners in Central New York are seeing with increasing frequency.

Rose rosette disease is is a viral-like disease carried by microscopic wingless Eriophyte mites. It is spreading unchecked throughout the Midwest, South, and East. This disease first appeared in the US in 1941. The main host of RRD is Rosa multiflora.

Rosa multiflora was introduced from Japan in 1866 both as an ornamental. It was soon used as a rootstock. The US Soil Conservation Service encouraged the planting of Rosa multiflora on farms, stripmined areas and along highways from the 1930s through the early 1960s. This rose can produces a prodigious amount of seeds. Birds eat the seeds and spread them, improving germination by their digestive process. The seeds are viable in the soil for up to twenty years.

Rose rosette disease causes vigorous growth with short intermodal distances (the space between leaves), thick reddish stems and thorns, contorted foliage, and witches brooms. The disease spreads from May through July. It kills roses infected with it within two to five years (depending on the size and health of the rose).

The first thing to do to prevent the spread of RRD is to eradicate any Rosa multiflora on or in the vicinity of your property. Be sure to remove the roots thoroughly and either burn the plants or dispose of them in plastic bags. Encourage your neighbors to do the same.

Reduce stress on existing rose plantings by watering, mulching and fertilizing. Some protection may also be provided by the use of horticultural oils or insecticidal soaps applied weekly throughout the growing season. Remember not to use any foliar sprays on rugosa roses, as that will damage or kill them.

Once a rose is infected there is no cure. Remove any garden rose affected. Be sure to remove all roots as well. Disinfect your pruning shears when moving from one rose to another.

Up to this point, I have not used and do not recommend the use of chemical sprays. There has been some research done on the use of miticides, like Avid, to help control rose rosette disease. If you are considering that approach, follow the directions provided with the miticide carefully. All bushes surrounding an infected bush should be sprayed every five days. To reduce the overall population, spray all your roses every two weeks from the end of April through September.

Rosa setigera, a native species rose is supposedly resistant to rose rosette disease. I have several cultivars with Rosa setigera in their background. I am particularly interested in seeing how they respond. I will be watching my roses carefully for the foreseeable future. You do the same!

Creating A New Bed For Roses

This time of the year, I am hungry to be outside in my garden. I look forward to the weeding, edging and mulching . It is a meditative practice for me. Of course, I like how the garden looks when I am done. But, it is too soon for these activities. Now is the time to figure out where I am going to put all those new varieties of roses that I have ordered. And as soon as it warms up some more, I can start creating new garden beds. I have used a variety of approaches and want to share what I’ve learned with you. We moved to our new property seven years ago this past September. It had been a hayfield. The soil is a gravel loam. There was a long swath alongside the driveway scraped clean by the bulldozer. I had dozens of roses in three gallon pots to plant, a house to unpack and settle in and the school year had just begun. Every day after school, I would be out there with a pick and shovel, digging holes for roses through October and November. I did not amend the soil. I dug each hole a little bigger than the pot. When they were all planted, I mulched the whole area six inches deep with bark mulch. Here's what it looked like the following spring. This is what that bed looked like several years later.

The following spring and summer, I added rose beds around the terrace and down the slope. That area had been seeded to lawn the previous fall. I rototilled the beds and worked in lots of compost. The roses I planted here were also in three gallon pots. This time I covered the area with about six inches of wood chips instead of bark mulch. The wood chips were free. This is what that area looked like a year after it was planted.

Here's what it looked like a few years after that. This view is from the other end of those beds, looking up towards the house.

The following year, I needed to add more garden beds, but didn’t have the time or energy to bring in compost and rototill. For these beds I used a method called sheet composting. I dug holes in the lawn and planted the roses. As before, the roses had well established root systems in three gallon pots. The lawn area around the roses was covered with thick layers of wet newspaper overlapped like shingles. This was covered with a layer of wet cardboard and topped off with about six inches of wood chips. The newspaper and cardboard kill the grass underneath and break down within a year or so. Here's a view of that bed a couple of years after it was planted. The women in the picture are my daughter, Sylvie, and my daughter-in-law, Jeanne. That's Jeanne's dog, Finn, watering the roses.

Every year, I add additional mulch to all of the beds. They have not been fertilized. No additional watering was done after the roses were established. Roses growing in beds created in these three ways are indistinguishable in terms of vigor and health. One would think that the beds that were rototilled and given additional compost would have shown better growth or that beds mulched with ground bark would be in better shape than those mulched with wood chips. Given decent soil conditions, it seems as if that additional work is not necessary. If you have heavy clay soil you might consider adding compost and rototilling. Adding sand will not improve the soil as well as adding compost. The climbers pictured below, lining the driveway were planted using sheet composting. I have added a bucket of compost around the base of each of them every other year or so. They look pretty good don't they?

I have made new beds every year we’ve been here. I’m thinking that this year might be the last year for increasing and expanding the rose beds, as it is taking me longer and longer to get them all weeded, edged and mulched. So that after this year, if a new variety is going to be added something else has to go. My family and friends are skeptical.

Own Root or Grafted? What's a rosarian to do?

There is a lot of talk about which is better, own root roses or grafted roses. It seems like a simple question, but like many simple questions, it depends. Before I answer that, let’s be clear on what we’re talking about.

Grafted roses are created by inserting a bud eye under the bark of the cane of the understock. Rosa multiflora is the preferred understock in our region because of its cold hardiness and ability to encourage vigorous growth. The newly grafted rose is planted out in a field. Once the bud has produced enough growth to support the newly created plant, the section of the cane above the graft is removed. The plant is dug up in the fall, soil is cleaned from the roots, the new growth is pruned back and the rose is placed in cold storage until the following spring when it is sold.

Grafting gives you a larger plant as you are planting a rose that has a two year old rootstock. Some varieties are more vigorous and healthy when grafted. Grafted roses “stay put” in the garden. They do not spread by suckers or runners. Unfortunately, if the top of a grafted rose is destroyed, you have lost the plant and the understock will take over.

Grafted plants can be purchased bare root or potted. Bare root plants need to be planted in the ground or in a large pot as soon as possible after purchasing. Contrary to what is common practice, the graft needs to be planted 3-4 inches below ground level in zones 5 or below. Over time, the part of the plant above the graft will root on its own and the understock will die. Planting this deeply prevents wind rock in the winter as the plant has multiple points of contact with the ground rather than just one stem. A trick I figured out in planting grafted roses is to plant them at an angle. You don’t have to dig as deep a hole, although you have to dig a wider hole. Grafted plants often have lopsided growth as the graft is on one side of the stem. By planting it at an angle you take advantage of this growth pattern.

Own root roses are rooted cuttings. Most nurseries typically sell one year old plants in band pots (about 2”x2”x6”). This size keeps shipping costs lower. These plants take about two years to catch up to a grafted plant. If the top of an own root rose is mowed over, broken, chewed by deer or rabbits or otherwise damaged, it will resprout from the roots and come true. Own root roses can form clumps or runners depending on the variety like many perennials.

I have found own root roses do best if planted in a larger pot rather than in open ground when first purchased. I use one gallon Rootmaker pots at this stage (www.rootmaker.com). These pots encourage quick growth of very fibrous roots. When the roots have filled this pot (usually within a couple of months), I move them up to a two or three gallon pot. It is worth the extra effort of gradually increasing pot size. I keep the own root rose in the larger pot for another two to three months, until their roots fill the larger pot. Then, they can be planted in a permanent location. Starting with an own root plant in April or early May and following this procedure, an own root rose can safely be planted out in September. This gives the plant the fall to establish its root system in open ground. Roots will grow as long as the soil temperatures are above 45 degrees or so. The following spring the plants are ready to take off.

As most folks are not interested in taking the extra time and care it takes to grow on an own root plant, I grow my cuttings to two or three gallon size before selling them. I offer both grafted and own root plants in my nursery. If you walked around my gardens, you would not be able to tell which rose was grown from a cutting or which was grown from a grafted plant. Nurseries sold own root plants many years ago but moved to producing and selling grafted plants because the reduced cost of production. It takes only one bud to produce a grafted plant. A cutting used to create an own root plant requires rooting a section of cane that has at least 6-8 buds.

So which do I recommend you buy, own root or grafted? I don’t think it makes that big of a difference. If you can only find the variety you want in a grafted plant, remember, you can take cuttings and grow an own root plant yourself later on. But that’s a topic for another blog.