What to Cut or Not

Downed Tree in Washington Park 3-13-19, Photo from The Denver Post

The mid-March "Bomb Cyclone," aka bombogenesis in Colorado has come and gone. The moisture in the form of rain, then wet snow was appreciated, the felled trees - not so much.

What's next? Probably more moisture, no worries, soon we'll be walking in the Easter Parade of colorful hats, bloom and green. First, we need to tackle the final late winter pruning chores. What needs to be cut or not?

So many questions ...

Should perennials be cut back in the fall right after they bloom or now in late winter? What about plants that have perennial personalities, but are also shrubby like lavender and sage, when do they need to be cut back ... should they be cut back at all? And what about summer-blooming shrubs? Not sure what to do with some of these commonly grown summer blooming shrubs - Rose of Sharon, hydrangea, butterfly bush, Russian sage and blue mist spirea?

Let's tackle these questions together ...

The late winter pruning and cutting back window is in full swing for trees, including fruit trees and many woody shrubs, if you haven't scheduled with a professional - get going. If you're a DIY - get going. Deciduous trees and many shrubs prefer being pruned while still dormant with no leaf or buds bursting forth in growth. It's much easier to see branching and areas that need be be pruned when these plants are naked. I covered trees and spring blooming shrubs in earlier blogs, so here are the links -

Winter Pruning Punch List

Just Say No to Beheading - Tree and Shrub Beheading

Perennial Cut Back ... yes .... to invigorate new growth and bloom for the season!

The rule of thumb for perennial blooming plants is to cut back all the dead, brown stems and foliage not cut in the fall to the ground where new growth will emerge soon - 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). Get rid of all that dead foliage and any new weeds popping up in the vicinity. Toss it all in the compost pile or bin if the foliage is disease free from last year's growth.

At this time there's no need to cut back iris or any other spring emerging bulb or tuber type perennials.

After cutting back, feel free to add some nice compost (homemade is best) around perennials to give them a little nutrient bump for the season as it breaks down more. Fertilizing blooming perennials is fine too, just don't add too much which may end up causing lots of foliage growth and less blooms. Excess fertilizer run off is not good either for our soils and waterways.

Wait a little longer for the woody type 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 bit of time to push new growth in the spring that begins on the older, lower woody stems. I wait until I see the new, tiny leaves on the culinary sage plants to cut off the clearly dead upper stems. This may be in April or early May. For lavender, that means cutting only a couple of inches down into new growth, obviously including any spent bloom wands from last year.

Summer Blooming Shrubs ... they need some attention too to look their best or not!

Russian Sage (Perovskia artiplicifolia) - a favorite of many who plant it, however if you're looking for mid to late season bloom and low water use (once established), consider these other great choices too - blue mist spirea, catmint, leadplant, Mohave sage or lavender.

Just whack it down hard to the ground this spring (leave a few inches up to a foot or so) to make room for another season of Russian sage.

Cut Blue Mist down to new leaf growth, photo from coloradoyardcare.com

Blue Mist Spirea (Caryopteris) - many people cut it hard to the ground every year, similar to Russian sage. Okay to do, but it's also fine to prune it every two to three years each spring. Just cut down to where you see new, healthy leaves forming at the base of the stems. They are easy to see. Basically, that's 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 twelve inches above a set of new buds. For spring blooming butterfly bush - Buddleia alternafolia, wait and prune spent blooms to new growth right after blooming.

Rose of Sharon bloom

Rose of Sharon (Hibiscus syriacus) - there's nothing quite so lovely as seeing late summer blooms on Rose of Sharon. I had three of them, but they were sorely damaged in the November 2014 Polar Vortex so they've since been removed. Plus Japanese beetles love them, so I decided against re-planting.

Try to ask yourself why a shrub needs to be pruned. With the three mentioned directly above, the simple answer is to get rid of last season's growth to allow it to bloom this summer. Another question to ask is when and how to prune. We answered those questions too. With Rose of Sharon, pruning isn't entirely necessary at all. It blooms on new wood each year so if the shape is a bit unruly or gotten a bit too tall for the space, or too close to a structure, by all means prune it now or by early May.

Hydrangeas ... so many species, sizes, bloom times and colors ... do they need pruning? 

Hydrangea macrophylla - these are the very popular big leaf or mophead of pink, violet, blue and red flowers ('Grateful Red'). 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.

Hydrangea arborescens - another popular group known as the Annabelle or smooth leaf types. 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 old stems back about a third of its total height.

Hydrangea paniculata - these easy to grow hydrangeas have mostly, lime green, white or white with pink tinged blooms rounded to pointed in shape. They bloom on new growth, flowering generally begins in August and lasts several weeks. Cut back now - hard, to right above a bud, leaving about two feet from the ground. Cut out the thin, pencil size wood which can't hold up the large flowers.

Hydrangea quercifolia - another classic - the oakleaf hydrangea - native to the southeast, deeply lobed, oak-like leaves with 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 any pruning (if any) after it finishes putting on its show. Bonus is its red, orange to purple fall foliage!

Hydrangea anomala petiolaris- if you're familiar with Michael Dirr, you know this climbing hydrangea is one of his favorite vines. Its aerial rootlets will cling to anything, but it prefers a north or east facing location (not hot south or west). With exfoliating bark and fragrant white flower clusters, what's not to love. This vine can climb, so give it room. Blooms on old wood, just prune out unwanted stray stems after bloom.

For additional information on pruning hydrangeas and photos of each species, click here.

Climbing Hydrangea from plantstore.co.uk