Recovering herbaceous perennials from frost damage in the nursery
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
The following tips will help nursery growers deal with frost-damaged plants. If you have specific questions, feel free to contact your local MSU Extension horticulture educator.
Many perennials in the field and in containers that were not protected from temperatures that reached the mid to upper 20’s were frost injured from this week’s cold snap across the state and will be showing the effects in the next few days. Most perennials will re-flush new leaves if the existing foliage was killed back. Daylily ferns and hosta, and others will flush out new leaves but at a slower pace than the initial flush and it may take three to four weeks under normal spring weather conditions.
To prune back or not to prune back?
There are two schools of thought here. Some say to leave the damaged leaf tissue such as hosta would have after frost. The foliage may be able to harvest sunlight and generate photosynthesis to help speed up the flushing of new leaves. Protect the damaged tissue with a foliar fungicide from Botrytis blight using such fungicides as Daconil, Vorlan, Decree or Heritage (see Extension Bulletin E-2782 Pest Management Guide for the Production and Maintenance of Herbaceous Perennials). Others say cut back the damaged foliage so it doesn’t lead to bacterial or fungal diseases. Pruning also makes the plants look better to the customer.
Day length continues to increase for the next 8 weeks helping leaf expansion, so that will be in your favor.
For other plants lightly damaged by frost, consider a light pruning or pinching back to remove the damaged tissue. Use a fungicide to reduce the risk of Botrytis blight or a bacterial infection. (See above-mentioned bulletin).
If irrigation for frost protection was excessive, you may have leached out your fertilizer from the media or the soil. Use a solubridge to check your EC levels and consider reapplying fertilizer if necessary.
Extra irrigation for frost protection can also increase your risk for Pythium root rot. Check root systems and if needed apply a fungicide like Truban or Subdue to protect roots against Pythium.