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FAQ's - Shrubs Fall/Winter

boxwood foundation planting

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We had ‘Knock Out’ roses planted this year by a landscaping company.  They did beautifully and bloomed for a really long time. Is there something I need to do for them this fall to prepare them for winter and when and how do I prune them?

We have two hydrangeas in our backyard. When should I prune them (fall vs. spring) and could you provide any details regarding the pruning process to obtain beautiful flowers in the spring/summer? 

I have established cherry laurels in the front of my house. This fall I noticed some branches that have brown leaves. Upon closer examination, I saw this white-fungus looking stuff on these stems. I am concerned that this will spread and cause further damage. What is this and what can I do to stop it?

What is the best way to deal with shrubs that are covered with either ice or snow? I certainly do not want to cause them any more harm but sometimes the ice and snow smothers them.

Last winter my Japanese hollies, rhododendrons and boxwoods suffered from winter burn. Is there something I can do not to prevent this from happening again this year?

Something has been gnawing at the base of my boxwood. It looked like some of the branches were wilting so I took a close look at them. I found chewing damage at the base of the stems. What could possibly be causing this? If it continues my boxwood will be dead.

We had ‘Knock Out’ roses planted this year by a landscaping company.  They did beautifully and bloomed for a really long time. Is there something I need to do for them this fall to prepare them for winter and when and how do I prune them?

 ‘Knock Out’ roses are very hardy in Maryland. They do not need any special care for the winter.  In dry falls, water them deeply before the ground freezes. They are pruned in March. Prune out any winter damaged, crossing or dead canes. You can then prune them back by about 1/3rd and shape them as desired.  Prune canes back to a major stem slightly above an outward facing bud.  During the season deadheading the spent blooms is not necessary, but doing so can stimulate the shrub to produce new flower buds.

We have two hydrangeas in our backyard. When should I prune them (fall vs. spring) and could you provide any details regarding the pruning process to obtain beautiful flowers in the spring/summer?

Pruning to control height or to remove old flower heads depends on the type of hydrangea that you have and whether the hydrangea flowers on the previous or the current year’s growth. 

Hydrangeas that flower on previous year’s growth:

Hydrangea macrophylla, Bigleaf hydrangea, Mophead (Pink & Blue types), Lacecaps

The bigleaf hydrangeas are the most common types in the landscape and flower on previous year’s growth. They can be susceptible to cold damage. Stems that have been damaged by cold should be pruned as soon as it is determined they are dead in the spring. Watch for new growth at the base of the plant.  If the plant has basal shoots that are about 6 inches in length, but the upper parts are bare, then the bare stems need to be removed. Otherwise, prune shortly after flowering is complete.

Some of the newer cultivars like “Endless Summer” bloom on both old and new wood, so if winter damaged, you may have summer blooms. To control height prune after the first flush of flowers.

Hydrangea quercifolia, Oakleaf hydrangea – Flowers on previous year’s growth.  Typically does not require pruning but if needed, in spring only remove dead wood.  Otherwise prune after flowering.

 Hydrangeas that flower on the current year’s growth:

Hydrangea arborescens, Smooth hydrangea, “Annabelle”, Grandiflora

Prune anytime from late summer until early spring. If pruning in the early spring, try to prune before leaves appear.

Hydrangea paniculata, Panicle hydrangea, PeeGee hydrangea, “Limelight”

Prune anytime from late summer until early spring. If pruning in the early spring, try to prune before leaves appear. Thin or cut back to previous season’s growth. Can become overgrown if not pruned.

Video-Clemson University - Pruning Lacecap Hydrangea

I have established cherry laurels in the front of my house. This fall I noticed some branches that have brown leaves. Upon closer examination, I saw this white-fungus looking stuff on these stems. I am concerned that this will spread and cause further damage. What is this and what can I do to stop it?

What you are noticing is not a fungus but a type of scale insect called white prunicola scale. This is an insect that sucks sap from twigs and branches. This can cause dieback, which is usually preceded by leaf yellowing, browning and premature leaf drop. The white substance you describe is the covering that is cast off by the male scales. If you look closely you may see round, orange objects which are the egg-bearing females. To control this pest prune out any dead or heavily infested branches. Then use a soft brush dipped in water to scrape off the remaining scale, as best you can. Spray with a horticultural oil, according to label directions, in the dormant season (November – March) or after the eggs hatch and the crawlers are present (this is when the insect is the most vulnerable to sprays). The timing for this is June, July or September.

What is the best way to deal with shrubs that are covered with either ice or snow? I certainly do not want to cause them any more harm but sometimes the ice and snow smothers them.

Once a winter storm hits it is sometimes better to leave well enough alone.  This is true if your shrubs are covered with ice. Disturbing ice laden stems can cause them to snap off.  However, if the shrubs are covered with snow gently brush it off using an upward motion.  Use a broom instead of a shovel because a shovel can damage bark. If you have multi-trunk evergreens it is best to tie them up or give them support before a storm strikes.

Last winter my Japanese hollies, rhododendrons and boxwoods suffered from winter burn.  Is there something I can do not to prevent this from happening again this year?

The plants you mention are broadleaved evergreens which are susceptible to “winter burn” or leaf scorch. Damage occurs frequently in January and February but can occur again in early spring during periods of fluctuating temperatures and when soils freeze and thaw.  Evergreens transpire (lose moisture) during the winter months and plants must replace lost moisture through their root system. Frozen soil prevents plants from taking up water causing leaves to curl and droop, then brown from the tips and margins, giving the leaves a scorched appearance. Windy conditions, when water is rapidly evaporating from needles, also exacerbates moisture loss. You can protect valuable, winter-burn prone plants by surrounding them with burlap or cardboard or constructing small, solid windbreaks located 18 inches from the plant on the exposed side. Next season, avoid fertilization or pruning in late summer, which stimulates new growth that does not have time to "harden off" properly and is much more susceptible to winter injury. If we experience a dry fall make sure to water susceptible plants before the soil freezes.  A 2-3 inch layer of mulch around the root zone would also be beneficial.

Something has been gnawing at the base of my boxwood. It looked like some of the branches were wilting so I took a close look at them. I found chewing damage at the base of the stems. What could possibly be causing this? If it continues my boxwood will be dead.

The most likely culprit is a small rodent called a vole (not a mole), also called a meadow mouse. This is a fairly common problem and can cause severe damage even to mature plants. They use snow or mulch as a cover and because they burrow in the soil they can cause damage below the soil line. Voles do not hibernate, so they are active year round, both day and night. Mow lawn areas regularly and pull mulch away from trunks of shrubs and trees. Use snap-type mouse traps with their trigger end in the runway or near areas where you see their exit holes to lessen their numbers. The best bait consists of peanut butter with a bit of apple. 

Please send us a question at Ask the Experts if you have a shrub question you would like answered. Digitial photos can be attached to your question.

FAQs - Shrubs Spring/Summer

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