QBARS - v11n1 The Behavior of Some Plants Since the 1955 Freeze

The Behavior of Some Plants Since the 1955 Freeze
By Bob Bovee, Portland, Oregon

R. decorum
Fig. 1 R. decorum
Cecil Smith photo

Last spring, following the freezing weather of November, 1955, thousands of rhododendrons, azaleas and other fine shrubs apparently dead were dug and destroyed. Time has proved that gardeners were often too hasty, and more patience would have prevented the destruction of many old and valuable plants.

A plant of the fine R. sinogrande from Dr. Rock No. 182 seed seemed dead. The bark was split from top to bottom of the trunk. But in October, eleven months later, new growth came from the roots. The same was true of R. argyrophyllum and several other big leaf species. Groups of the tender R. burmanicum and Gaultheria wardii froze to the ground. Every plant recovered, put out strong new growth and today are finer and more bushy than they were originally. R. ciliatum and its lovely hybrids "Cilpinense" and "Snow Lady" were killed to the ground in most gardens. But soon they sent out new growth from the base of the plants and then set bloom buds.

R. ciliatum
Fig. 4. R. ciliatum
Cecil Smith photo

Damage resulting from the November weather was very spotty. Plants killed in one part of a garden would be in good condition a hundred feet away, and would bloom in a garden a half mile distant. Magnolia soulangiana bloomed well and was not harmed in many gardens. But one 15 foot plant bloomed heavily then immediately died while younger plants fifty feet away came through unharmed. The finest plant of Magnolia stellata I have seen was killed to the base. In other locations, even where it was colder and more exposed, this magnolia was not harmed.

A 20 year old plant of R. decorum , hardiness rating H4, grown in full sun and exposure, was not hurt except for loss of 25% of its buds. It bloomed beautifully. While a 30 year old plant of R. fortunei , rated H2, grown in a protected spot in light shade was killed and made no recovery. The R. decorum hardened its wood early. The R. fortunei was still in soft growth. Pieris japonica grown in full exposure was often not severely damaged and bloomed. But many plants grown in the shade, recommended for this plant, were heavily damaged.

Plants growing in lath houses were more heavily damaged than the same kind and size plants growing in the open field. In many gardens there was a marked difference of the effect of exposure to plant damage. Plants in the shade, even light shade were killed or heavily damaged, while those grown in the sun suffered only bud loss and leaf burn.

A group of plants of the Maddenii series, grown outside for many years in a protected garden, froze to the ground. Many recovered from the roots. The behavior of R. 'Lady Roseberry', R. 'Lady Chamberlain' and R. 'Royal Flush' was surprising in some gardens. In one garden where they were grown in light shade, two of three large plants of 'Royal Flush', often considered the most tender of the group, came back from the roots. About half the plants of R. 'Lady Chamberlain' survived. All plants of R. 'Lady Roseberry' were killed. In other gardens R. 'Lady Roseberry' came through in quite good condition.

Plants which hardened their wood early undoubtedly came through in the best shape. This was true of R. williamsianum and its hybrids which in most gardens were unharmed and bloomed well. R. thomsonii was killed or badly hurt, even big old plants over 20 years old. But we saw one seven or eight foot plant growing fully exposed to the hot west sun come through with only the loss of its buds, some foliage and a few limbs. Plants of the Loderi group, heavily damaged in many gardens were often only slightly hurt in more exposed locations.

Old plants of R. 'Jan Dekens', 'Pink Pearl' and others were found with the cambium tissue completely brown. This seemed to have no effect on growth and by fall the cambium layer was green again. Rhododendrons of the triflorum series were perhaps more heavily damaged than those of any other series. Where they were grown exposed to the sun the damage often was lighter. R. schlippenbachii seemed to love the climatic conditions of last year. It bloomed wonderfully well.

R. ciliatum R. schlippenbachii
Fig. 2. R. ciliatum
R. Henny photo
Fig. 3. R. schlippenbachii in the Crystal
Springs Test Garden
Cecil Smith photo

Damage resulting from the November weather was not nearly as great as first thought. Badly hurt rhododendrons and other plants have made a fast recovery. In our garden this was particularly true of plants which were heavily mulched with sawdust. Many plants proved to be tougher than was thought.

Growing plants in a good deal of sun and withholding water late in the summer forces them to harden their wood. They go into winter in better condition. Sun helps plants to bud heavily. Flowers may not last as long and leaves often become smaller, but the plants may live longer.