What to ask, and why, when pruning roses

For The Union-Tribune

Next spring I will be joining a rose tour in France, so I need to brush up on my French. I gathered up my French books and started by reviewing the chapter on how to ask questions, because if you want to know where to go, how to get there, what to do and why to do it, you really need to ask the right questions. Asking the right questions is also the approach that helps beginner rose growers understand why and how to prune roses. A brush up on pruning techniques can also be helpful for seasoned rosarians.

Why do we prune roses?

Pruning revitalizes our roses. It opens the plant to light and air circulation which minimizes disease. When we prune, we enable the bush to resume growth in the early spring on strong, vigorous canes. This maximizes the health of the plant and the number and beauty of its blooms.

How do we prune?

Start by looking at the bud union (the base of the grafted rose). Determine which are the ‘keeper’ canes. Keeper canes are vigorous, healthy and new (green) canes. Canes that are dead, spindly or damaged must be cut out. Older canes can be pruned out if there are enough keeper canes. An old cane becomes a keeper when there is a newer cane emanating from it further up the bush.

What other canes do we prune out?

Crossing canes can wound each other with their thorns and the wounds can provide entry to fungal pathogens. Removing weaker crossing canes reduces risk while allowing more light and air into the bush, resulting in improved blooms.

A sucker is a shoot that comes not from the bud union but from the rootstock of a grafted rose. Its foliage and flowers and growth habit will look different from the grafted rose. Trace the sucker back to its origin and cut it out to prevent it from ‘high jacking’ your purchased rose variety.

When we are removing an entire cane, where do we make the cut?

Removing canes at the bud union creates space and encourages the development of vigorous new canes, referred to as basal breaks.

What is the bud union?

Roses can grow on their own roots, but most roses are grafted on the roots of ‘Dr. Huey’ or another rootstock. The bud union is the swollen junction between the roots and the canes on a grafted rose.

Which canes do we leave?

Most rosarians keep all new, healthy canes. Some growers who exhibit their roses will leave only 5 to 7 strong canes on a bush, so the rose bush puts its energy into producing the biggest blooms.

How much do we prune?

In San Diego, we do not need to prune as severely as they do in colder areas. We don’t usually prune below knee height.

Generally, we cut about one-third off the height of our hybrid teas. On hybrid teas we want one large bloom per stem so after the basic clean-out of dead and damaged growth, we cut back to an outside bud-eye on a cane that is thick enough to support the desired future bloom. Stems that are not as thick as the diameter of a pencil are removed.

We cut back only a quarter of the height on our floribundas, polyanthas, shrub roses and David Austin roses. We can leave some branching on floribundas and shrubs, but we should aim to prune down to a stem diameter that will support the quality of blooms or cluster of blooms we want.

On miniature and miniflora roses, some people prune off the top third with hedge shears and then open up the centers by cutting out twiggy growth with pruners.

Do all canes need to be pruned to the same height?

No. Trying to achieve this could result in having to prune the canes shorter than they need to be.

Where on the keeper canes do we make our pruning cuts?

Having figured out approximately how much to cut off, we make each cut at about 1/4 inch above a leaf with five leaflets. We choose an outward facing bud eye as this prompts the rose to grow in that outward direction and away from its center. The cut does not have to be slanted. When you prune a cane, the pith should be creamy white; otherwise make your cuts further down the cane.

What is a bud eye?

There is a bud eye where a leaf is or was attached to a rose stem or cane. The bud eyes spiral around the stem so there are inward-facing bud eyes and outward-facing bud eyes. The bud eye resembles a small reddish bump or swelling. Bud eyes that are further down the stem (where it is thicker) are generally more vigorous.

Are climbers pruned differently?

All classes of roses need to have dead or damaged canes cut out. Other than this similarity, climbers are pruned very differently from other roses. The main canes on a climber are not pruned but trained horizontally to encourage lateral growth because climbers bloom off lateral shoots. Our pruning cuts on climbers are made not at a bud eye on the main cane but at a strong bud eye on each of the lateral shoots growing off the main canes.

How do we prune old garden roses?

Old garden roses that bloom only once need just a light grooming after their flowering has finished, and very little pruning in January other than the removal of old and dead growth.

When do we prune?

In San Diego, we prune our roses in late December and January. Colder regions wait until there is no longer a danger of frost.

What else do I need to know about pruning?

Cut off all the remaining leaves from the plant. Cutting the leaves off as opposed to stripping them off by hand is preferable as foliage pulled off the plant can wound the stem and leave it open to entry by pathogens. Don’t let your rose garden start the new year with last year’s disease and insects which may still be lingering on its old leaves. Clean up and dispose of all clippings, leaves and petals around the base of the plant to get rid of dormant spores of fungi and over-wintering pests.

Do roses have to get pruned?

No, but re-read the article and ask yourself why you would skip pruning.

What tools do we use?

We need a good sharp pair of by-pass pruners. Other essentials are a sharp pair of long-handled loppers and a pruning saw. To protect our hands and forearms, good gauntlet gloves are imperative.

Free pruning workshop

The San Diego Rose Society invites you to bring your gloves and pruners to a no-charge hands-on rose pruning workshop at the Inez Parker Memorial Rose Garden in Balboa Park from 9 to 11 a.m. on Jan. 10. The Master Gardener tool committee will be on hand to perform a complimentary cleaning and sharpening of one garden tool for each attendee. For more information: sandiegorosesociety.com.

Perwich is a member of the San Diego Rose Society, a Consulting Rosarian and a Master Gardener with UC Cooperative Extension. For more information and advice, visit rose-harmony.com.