Spring in Colorado is grand if you’re OK with switching between a heavy jacket and a tank top. We never complain about spring rain or even snow since all moisture is welcome and needed for water use, landscapes and agriculture.

Here’s your April outdoor plant pruning and vegetable tips list for when the weather is cooperating.

Perennial cutback

The general guideline for perennial blooming plants is to cut back to the ground all the dead, brown stems and foliage that wasn’t cut in the fall. This is where new growth will soon emerge; some are already showing their green. This can be done when the ground dries out between now and before plants are really putting on new growth (April-May). To allow for new spring growth, get rid of all that dead foliage and any new weeds popping up. Toss it all in the compost pile or bin if the foliage is disease-free from last year’s growth.

The general guideline for perennial blooming plants is to cut back to the ground all the dead, brown stems and foliage that wasn't cut in the fall. (Betty Cahill, Special to The Denver Post)
The general guideline for perennial blooming plants is to cut back to the ground all the dead, brown stems and foliage that wasn’t cut in the fall. (Betty Cahill, Special to The Denver Post)

After cutting back, feel free to add some quality compost around perennials to give them a little nutrient bump for the season. Fertilizing blooming perennials is fine during the growing season; just don’t add too much or it may end up causing lots of foliage growth and fewer blooms. Excess fertilizer runoff is not good for our soils and waterways.

Wait a little longer to prune the woody types of perennial herbs like lavender and culinary sage. These plants don’t like being cut when they are still dormant, and it takes them a little time to push new growth in the spring that begins on the older, lower woody stems. Wait until you see tiny leaves on the culinary sage plants to cut off the clearly dead upper stems. This may be in late April or May. For lavender, that means cutting only a couple of inches down into new growth (obviously including any spent blooming wands from last year).

Popular spring and summer blooming shrubs

  • Russian Sage (Perovskia artiplicifolia) is a favorite of many homeowners. However, if you’re looking for mid- to late-season bloom and low water use (once established), also consider these other great choices: blue mist spirea, catmint, leadplant, Mohave sage and lavender. Cut Russian sage to the ground in spring (leave a few inches up to a foot or so) to make room for another season of growth and bloom.
  • Blue Mist Spirea (Caryopteris), which blooms in late summer, is often cut hard to the ground every year similar to Russian sage. This is OK, but it’s also appropriate to prune it every two to three years in spring. Cut down to where you see new, healthy leaves forming at the base of the stems. Basically, it means cutting off the spent top flower growth, totaling about half or a third of the entire plant.
  • Butterfly Bush: Just like blue mist spirea, Buddleia davidii (butterfly bush) can be cut every couple of years each spring or every year. Cut down to about 12 inches above a set of new buds. For the spring-blooming butterfly bush (Buddleia alternafolia), wait and prune spent blooms to new growth right after blooming.
  • Rose of Sharon (Hibiscus syriacus): There’s nothing quite so dramatic and head turning as seeing late summer blooms on Rose of Sharon. Yearly pruning isn’t entirely necessary. Rose of Sharon blooms on new wood each year, so if the shape is a bit unruly or has gotten a bit too tall for the space or too close to a structure, by all means prune it now or by early May.
  • Hydrangea pruning may seem overwhelming. To simplify, examine the stems each spring and look for obvious swelling buds. If buds look like they will open soon, then these types should not be pruned now; wait until after they finish their bloom. They formed these buds last fall (old wood) for this year’s bloom cycle. Hydrangea shrubs that bloom on new wood will grow buds this spring, so they can be pruned in late winter to early spring. Pruning during the growing season may risk cutting off flower buds. There are five commonly grown hydrangeas in our area.
    A relatively new pink hydrangea called Invincibelle. This group blooms on new spring growth so a good thorough prune will bring rich rewards in summer blooms. (Ed Post, provided by Proven Winners)
    A relatively new pink hydrangea called Invincibelle. This group blooms on new spring growth so a good thorough prune will bring rich rewards in summer blooms. (Ed Post, provided by Proven Winners)
     
    1. Hydrangea macrophylla (the very popular big leaf or mophead of pink, violet, blue and red flowers like Grateful Red and Endless Summer. This group is considered the classic hydrangea in looks and growth. The buds are set on the previous year’s growth, but some varieties also set secondary buds that flower later in the summer. Pruning now should be limited to removing dead wood, wait until right after flowering to tackle shaping or just leave alone if they are perfect for your viewing pleasure.2. Hydrangea arborescens is another popular group known as the Annabelle or smooth-leaf types. Bloom colors are mostly white or creamy white. There’s a relatively new pink called Invincibelle. This group blooms on new spring growth so a good thorough prune will bring rich rewards in summer blooms. Cut stems back about a third of total height.

3. Hydrangea paniculata are easy-to-grow hydrangeas with mostly lime green, white or white with pink-tinged blooms round to pointed in shape. They bloom on new wood, with flowering generally in the summer, and last several weeks. Cut back in early spring to right above a bud, leaving about two 2 from the ground. Cut out the thin, pencil-size wood which can’t hold up the large flowers. Limelight is a great choice for hedges and containers, and is available in tree form as well.

4. Another classic is the oakleaf hydrangea (Hydrangea quercifolia), which is native to the Southeast. It is deeply lobed with oak-like leaves and showy, white summer flowers. This group produces flowers on old wood like the macrophylla group, so simply prune any dead wood in the spring but wait and do pruning (if any) after it finishes putting on its show. These prefer some winter protection. Bonus with its red, orange to purple fall foliage!

Limelight hydrangea is a great choice for hedges and containers, and is available in tree form as well. (Chris Brown, provided by Proven Winners)
Limelight hydrangea is a great choice for hedges and containers, and is available in tree form as well. (Chris Brown, provided by Proven Winners)

5. Hydrangea anomala petiolaris, or climbing hydrangeas, are beautiful when planted in areas with wind and late afternoon sun protection like a north- or east-facing location. Its aerial rootlets will easily cling but appreciate some support. With exfoliating cinnamon-brown bark and fragrant white flower clusters, what’s not to love? This vine can climb, so give it room. It blooms on old wood, so just prune out unwanted stray stems after blooming.

Vegetables

Get a jump on your early spring planting season by warming up in-ground and raised beds with 4- to 6-mil clear or black plastic. Anchor the plastic with boards, brick or soil. Leave it in place for a couple of weeks.

When soil temperatures are 40 degrees or warmer, it’s safe to plant hardy cool-season transplants including broccoli, cabbage or direct-seeded kohlrabi, peas, lettuce, onions and onion sets, radish, spinach, turnips and potatoes.

Welcome to the new outdoor home-grown gardening season.

Denver, CO - MARCH 15: Denver Post garden contributor Betty Cahill demonstrates how to properly divide and move plants for this week's DPTV gardening tutorial. Plants are divided or moved because they are overgrown, overcrowded, lack vigor or are in the wrong place. Spring is the best time to move summer and fall blooming plants. (Photo by Lindsay Pierce/The Denver Post)

By | Special to The Denver Post

 

Betty Cahill is a freelance writer who speaks and writes about gardening in the Rocky Mountain Region. Visit her site at http://gardenpunchlist.blogspot.com/ for even more gardening tips.