Late Frosts and what to do?
[Parts of this article was originally published within our email Newsletter, but we wanted it to be accessible as an archive posting for future reference. If you are not signed up for our newsletter, here is the link and a new window will open so you do not lose this webpage.]
(Late April/Early May, 2012)
Several areas across the USA reported cosmetic damage due to the weather suddenly changing within the past few weeks, catching plants and gardeners by surprise. After many days of unseasonable warm and pleasant days with soft new growth on trees, shrubs and perennials, temperatures suddenly dropped into the high 20's and low 30's, causing some varieties of lilies to resemble sticks with limp green leaves.
If buds had not yet been formed, with stems staying in active growth, the only damage will be visual - a ring of browned leaves at the upper portion of the plant. The damaged leaves are not enough to stop growth and the stem should flower normally. However, be on the outlook for signs of fungus beginning - round brown spots with clear centers on leaves or brown spots on flowers later in the summer. Spray with a good copper-based fungicide, such as used for Roses for a preventive measure. Apply as needed on a dry day until the weather settles.
At 30 degrees F. (two degrees of frost), leaves will fold down like the top photo, but when the sun comes up, they will miraculously turn upwards again with just a little browning of the leaves as shown 2 hours later. Heavier frost will cause damage to the most tender leaves at the tops of stems, but in many cases they will quickly grow new unmarred leaves.
The lily shown above was sprayed with a copper-based fungicide as a safety measure against Botrytis becoming a problem should the "up and down" weather continue. The blue tint is residue from fungicide, coupled with a "spreader-sticker" to adhere the spray to the leaves. Notice the frost damaged leaves that have turned brown but the fresh new leaves emerging in the the top center where buds will eventually form.
Only a few varieties in a garden may show frost damage, Orientals and Asiatic lilies are most resistant, with pure Trumpet lilies being more likely to be damaged, and the OT hybrids (Orienpets) about halfway between but they will generally "grow" out of it as the specimen shown above and not impact future growth of the lily bulb.
Very late frosts in mountainous areas can happen as late as June - if weather forecasting can give you a "head's up" - simply draping Reemay (non-woven polyester) fabric over the stems will help if the stems are not too tall. If buds have been damaged, they will turn brown and you should cut away any browned tops with a knife or pruners dipped in bleach water to avoid spreading any fungus. Try to retain as many leaves as possible to nourish the bulbs and continue to water and fertilize. Even if you should lose the entire stem, the lily bulbs themselves will not be harmed - other than losing some girth - and all should be well next spring and summer.