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Butterfly Bushes damaged by cold

Whacky spring weather was brutal to 'subshrubs'

By: Sandy Feather ©2012
Penn State Extension

Q. My butterfly bush (Buddleia spp.) pushed new growth early due to the warm weather that was killed by frost. Should I go ahead and cut it back now, or should I wait to see if it starts to grow again?

A. While people were enjoying the much-above-average temperatures in mid-March, many plants joined in the fun and started growing far earlier than normal. It was not a big surprise that normal March weather returned, including a few heavy frosts that damaged such tender new growth. While most plants will bounce back with no problem, some may not be so lucky, especially plants such as butterfly bush that are classified as subshrubs. These are plants that are woody near the base of their stems, but produce herbaceous rather than woody new growth annually. Subshrubs, like the butterfly bush, are more susceptible to freeze damage over the winter and to frost damage as new growth begins in spring.

Butterfly Bush
Buddleia 'Peacock'

Subshrubs do not go completely dormant in winter as hardy woody or herbaceous plants do; instead they are quiescent or resting. This allows them to respond to warm temperatures more quickly than true herbaceous or woody plants. Sometimes they do not have the stored energy to push new growth a second time if the first flush is killed by frost. It is not unusual to lose these plants when we have a hard frost after they push new growth in spring.

Butterfly Bush
Buddleia 'Honeycomb'


 


Avoid the temptation to prune your butterfly bush back until later in spring, once we are past danger of severe frost, usually mid-May. Your plant may have the energy to push new growth a second time, but if it is hit by a frost again, it probably will not push out a third time. In more “normal” spring weather (whatever that is!), we would still recommend not pruning subshrubs back until late spring because pruning pushes new growth. That is why it is not a good idea to prune them in fall, either - the new growth might not harden off in time for winter.

Buddleia
Butterfly Bush 'Potters Purple'

Be careful when you prune your butterfly bush not go lower than five or six leaf buds from the ground. Beyond that, you get into old wood that will not break new growth.


In addition to butterfly bush, other subshrubs that are common garden plants include:

• root beer hyssop (Agastache rupestris)

• artemesia (Artemesia spp.)

• blue-mist shrub (Caryopteris spp.)

• St. Johnswort  (Hypericum spp.)

• lavender (Lavandula spp.)

• ornamental oregano (Origanum rotundifolium, O. laevigatum)

• common oregano (Origanum vulgare and cultivars)

• Russian sage (Perovskia atriplicifolia)

• rue (Ruta graveolens)

• culinary sage (Salvia officinalis and cultivars)

• lavender cotton (Santolina chamaecyparissus)

• thyme (Thymus spp.)

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