Pruning Xeric Plants

The best part of early spring is watching growth appear on plants that have been dormant all winter. And since we can’t plant vegetables until after the last frost, I need something to do in the garden on nice spring days. We had two of those this weekend, and we got busy pruning our xeric garden and front beds.

lavender-redbud-new-mexico
Pruning woody lavender requires only some shaping and removal of stalks as or after they bloom.

Pruning can be scary for new or hesitant gardeners. I’ve often hated to cut off any of the new spring growth that’s already begun. But I have to remind myself that cutting a plant back saves water. Here’s why: The plant’s roots can only provide so much water and nutrients. If gardeners leave too many branches above ground, the roots struggle to feed every branch, leaf or flower all the way to the end of the plant. It’s like filling a bowl of cereal with milk. The more cereal in the bowl, the more milk is necessary to coat or soak the cereal (sorry, but I love food analogies).

butterfly-bush-pruned-to-ground
This butterfly bush looks like mostly sticks right now, but it’s loaded with new growth at the bottom.

I’m still having to remind myself that by cutting a plant further down, I actually help it grow more vigorously than if I merely trim it a little bit. The mature plant regrows to a size that matches its established root system. We cut several plants nearly to the ground, including Russian sage (Perovskia atriplicifolia) and butterfly bush (Buddleia). I have yet to kill a plant from vigorous pruning. A few times (like with forsythia), I pruned at the wrong time and it affected shape or flowering. But you can always correct shape and learn from your mistakes.

butterfly bush in summer after heaving pruning
Here’s last year’s butterfly bush (to the right and center) after a similar prune last year. It shoots up to six to eight feet tall.

Around here, Tim typically trims the trees and I handle shrubs. I start with roses as soon as any new growth appears, and your local master gardeners most likely recommend a window of time that’s best for roses and other common plants in your area.

Here are a few pruning tips for plants that grow in the arid high desert and intermountain regions:

  • In early spring, prune plants that flower in summer. Those that bloom in spring (like forsythia, clematis, flowering quince and dogwood) do best if pruned after they flower. They form buds in the fall, and spring pruning removes the flowers. The same goes for spring-flowering bulbs, such as iris, although they shouldn’t be pruned immediately, but when stalks and leaves begin fading or turning brown. In this case, the plant above ground gives energy back to the bulb underground.
forsythia blooms
Our forsythias are loaded with spring blooms; I pruned them last summer.
  • Nearly all trees should be trimmed in winter, while dormant.
  • Some gardeners prefer to prune in fall for a more manicured look during winter. We don’t do that for a few reasons. One is that a late warm period can cause the plants to grow again, and they need to begin storing energy for winter; a heavy late pruning can make the plant more vulnerable to cold. The other reason is that birds feed on the flower heads all fall and winter. And the spent blooms and stalks look fine in a natural, xeric design.
yarrow blooms
The bright yellow blooms of yarrow in summer.
  • Many plants only need to have their dead stalks removed. For example, yarrow and Angelita daisies have stalks that rise above the foliage. You can use trimmers or sharp shears to remove spent stalks.
yarrow after winter xeric
Here’s what the yarrow looked like a few days ago. It was ready to lose the dried flower stalks.
pruning yarrow
The pruned yarrow is now ready to put energy toward developing new flower stalks.
  • It’s best to avoid cutting into the woody, feeder branches of plants such as lavender and rosemary. Trim them for shaping only, and harvest ends of rosemary or cut lavender flower stalks for drying and other uses.
  • The more center and crossing canes or branches you can remove, the better. If you have a native rose that is seriously overgrown or pruned poorly, consider cutting it to the ground once, just to reinvigorate the plant and let it return to a more natural shape. It might take a year or two to get the plant into the shape you like.
yellow
I’m gradually cleaning up this native rose. Last year, it bloomed so pretty in mid-April. This year, I pruned it more severely, but it’s taking on new growth.
  • Some plants do better with a second cutting right after they bloom so you can enjoy another summer show of color. An example is catmint (Nepeta). Shearing off about one-third of the plant at the top gives it energy to regrow flowers. Of course, many annuals, such as California poppies (Eschscholzia californica) or blanket flowers (Gaillardia) bloom best if you deadhead them, or remove spent blooms, throughout the summer.
Our catmint was already blooming and attracting bees by the time I got to it. But it's so forgiving (and at times invasive here). I pruned off dried stalks and shaped the plants for a wilder look around the path's rock border.
Our catmint was already blooming and attracting bees by the time I got to it. But it’s so forgiving (and at times invasive here). I pruned off dried stalks and shaped the plants for a wilder look around the path’s rock border.
  • We usually give our xeric plants a good soaking right after trimming them to help them through the shock and stimulate growth. But that’s the only time we water almost all of our established xeric plants.
dogwood and catmint
Best of both seasons. The dogwood still has its winter red, but plants like catmint are blooming.

If you’d like to learn more, including where to cut shrubs for optimal growth, check out this publication from the University of Georgia extension office.