Frost Tolerance of Hostas
by James B. Hoteling
Johnson City, New York

May 15, 1996, 6 am, 18 degrees Fahrenheit
July 11, 1996, 6 am, 39 degrees Fahrenheit

In previous years, I have had freezes on June 17-20. How do you deal with this and keep your sanity as a gardener? A number of articles in past issues of The Hosta Journal have addressed covering hostas in spring, and emergence times of hostas, both important for controlling spring frost damage. If you live in a “frost pocket”’, as I do, both of these issues are important along with a few other tricks – some learned by accident, others by neglect.

Most weather forecasts today give the expected low temperature for the overnight period, and then say “colder in valley areas”. Sheltered valleys are even more of a problem. In my area (the Binghamton-Johnson City-Endicott-Vestal, New York region) is the confluence of two rivers, the Susquehanna and the Chenango. On cold mornings in the spring and early fall these larger river valleys are usually filled with fog, effectively buffering the cold temperatures. My house is located in a sheltered valley just far enough from the large rivers that the fog does not accumulate. I therefore get some unusually cold late spring temperatures. To make matters worse, I moved to a new location in 1991 and was foolish enough to relocate to another “frost pocket” area.

I have learned some tricks to overcome this problem, the worst of which is not to grow many of the late freeze-susceptible forms such as H. plantaginea and ‘Royal Standard’. Most fragrant hostas are derived from these plants, posing a real challenge to grow them. My challenge to breeders is to bring fragrance into a new plant without the tenderness to frost. Knowing which plants are the most frost sensitive and covering them is an obvious solution. When the plants are small, this is quite easy using nursery pots. I then graduate to large rolls of white fabric frost clotH. A number of problems with this solution are the time it takes to cover and uncover, wind blowing off the covers, and often when I am leaving for work it is still below freezing and I cannot uncover.

Choosing the right location for certain frost sensitive hostas helps cut the losses. The east side of a house warms up early in the spring and growth starts early. The north side of the garage stays in a shadow of the building and the ground will stay frozen for several weeks later, slowing the emergence. Under a large white pine that harbors a large number of varieties is another protected area. as the cool temperatures under the tree cease slow emergence.

One trick learned by accident involved this same pine. Since it was in the garden bed furthest from the house, it did not get the cleanup priority in the fall or early spring. The pine needles and leaves covering the plants remained on until late May. While ‘Sum and Substance’ by the house was 24 inches high by 36 inches wide, most plants under the tree were just emerging. With only a few plants covered, this bed received little damage after the 18 degree night on May 15.

Cultivar choice remains the best method of avoiding frost damage as it is in avoiding slug damage. This is fine for many of the gardens I design where only a few different varieties need be used. But for collectors it’s not that easy – we may want them all. The Fortunei Group, with plants such as ‘Fringe Benefit’, ‘Francee’, ‘Green Gold’, ‘Gold Standard’, ‘Patriot’, etc., are quite frost tolerant. If I am in a hurry and cannot cover everything, these are left uncovered. Even if they do get some frost damage, they are fast to recover. Sieboldiana Group and Tokudama Group are very slow to recover as they tend to push only one good flush of growth in a season. These become covered religiously.

A list of frost sensitive and frost tolerant plants would be nice to accompany this article, especially newer cultivars. I have the perfect laboratory to test the plants. The problem is that it may take another growing season for them to recover. With closer observation I will begin to accumulate such a list. Anyone with such information, whether of one variety or many, please let me now: James B. Hoteling, 325 Death Valley Road, Johnson City, NY 13790.

So you breeders out there, while you are looking for your fragrant flowers, red leaves and branched bloom scapes, do not forget spring frost tolerance!

from The Hosta Journal vol. 28-1 p.87 1997


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