Suggestions and Problem Solving for Growing Tree Roses in the North
Tree roses are a wonderful sight in the formal garden and a properly grown one is a horticultural masterpiece.
Unfortunately, too many gardeners get sold these plants without clear directions or an understanding of what they are trying to grow.
And it is important to understand the basics because how you have to treat this plant as if you were growing two separate plants.
Grafted Tree Roses
You see, the flowering portion (hybrid tea/ floribunda etc) is grafted onto a trunk (of a 'Dr Huey' rose or sometimes a Multiflora rose). These two root stock roses for trunks are grown in a field and when the rose nursery wants to graft some rose trees, these root stock roses are dug up and the top is sawn off when they are dormant to produce a root with a single large trunk.
The rose nursery then grafts a flowering portion on the top of the single trunk. Grows it for a season and then sends it to a retail nursery as a tree rose. They graft all kinds of roses on top of the trunks and this is why you'll often see a 'Queen Elizabeth' tree rose next to a 'Queen Elizabeth' hybrid tea rose. They are the same flowering rose - only one is grafted onto a tree trunk and the other is grafted onto a root without the trunk.
And you buy it.
Growing Two Roses
You have two roses to grow - one on the top and the one on the bottom. (If you're on the West Coast - you likely have a 'Dr. Huey' root and the East coasters tend to have R. multiflora roots)
You want to feed it and prune it according to the directions found on these pages (see the growing techniques section). There is no distinction between how to grow, prune, plant, smell and enjoy these plants.
The major difference comes with overwintering this plant.
Your objective is to keep both the top and the bottom alive during the winter and this is a bit of a challenge. That top graft is very tender.
There are a wide variety of techniques on the web for protecting these plants - let me summarize.
In areas where the temperatures do not get down to -5F, you prune the top as you would any rose in preparation for winter. Then wrap the entire tree rose with heavy insulation of some kind (like a flexible Styrofoam). Cover the insulation with burlap and then duct tape the burlap so it will not fall off the plant. This will keep off most frosts and a bit of freezing weather.
In areas colder than this, you really only have two choices to protect this plant for the winter (if you don't count taking it south with you).
You can dig it up, pot it up and take it indoors so it doesn't freeze at all. You will need to keep the roots between 35-45F all winter so they stay dormant and do not freeze. The soil needs to be damp - not dry at all - but not swampy either. I'd suggest you check the pot every few weeks and water if the soil is dry. If the soil is not dry, simply walk away and do not water.
Or, you can dig a trench 12-18” deep in your garden. Dig up the tree rose, prune the top and then lay the tree rose into the trench and backfill it with soil. Mulch over top of the tree rose with organic mulch to provide some extra protection. Mark the rose grave with a marker so you don't forget where to dig it up in the spring.
Nursery Advice Problem
Some nurseries will tell you to dig a trench at the base of the rose, dig up half the roots and then lay the rose over into the trench.
This is almost a sure way to kill half the roots in a cold climate. Those roots dug up and rolled upwards are usually exposed to freezing temperatures. It is far better to dig a deep trench, dig up all the roots and lay them all in the trench. If you do this lay down over into the trench system, then definitely add extra soil over the trench (12" would be fine) and then mulch. The key is to protect both the bottom and that tender graft from freezing temperatures.
Tie Them Up
You can tie both the tops and roots together with twine to make them easier to bury
After the rose has been buried, it is an excellent idea to flood the area with water. This settles the soil around the rose roots and doesn't allow them to dry out at all.
In the spring, dig up and replant the rose. Start again.
If your rose starts throwing new shoots from the base, and the top is not growing, you have a dead top. The root stock is throwing shoots and unless you want to grow one of these, you can dig it up and toss it away.
If your top is growing and the base is still throwing new shoots, simply rip up (use the claw end of a hammer or cut very close to the root with pruners) the shoots coming from the ground. This happens sometimes when the top is not vigorous enough to provide enough energy to the root. Feed this plant compost to encourage new top growth.
Florabunda Rose 'Shockwave'
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A wide variety of rose plant resources from multiple suppliers - do not buy seeds (too good to be true category)
All of Doug's Ebooks including how to grow roses in tough climates