Home Gardens

Bay of Plenty Beacon, Volume 12, Issue 25, 27 February 1948, Page 6

Home Gardens

(By J. W. Goodwin, N.D.H. (N.Z.), F.R.H.S., Massey Agricultural College.) HALF-HARDY TREES AND SHRUBS In discussing half-hardy trees and shrubs for autumn flower, it is necessary to define what is meant by plant hardiness. The general classification of the hardiness of plants is really a guide to the approximate amount of frost a plant will survive.

“Tender” .includes those which will not stand any frost and those which may withstand up to 4 degrees. “Half-hardy” withstand from 4 to 10 degrees, “hardy” 10 to 16 degrees and “very hardy” 16 degrees upwards. At its best, this is only approximate as a great deal depends on the state of plant growth when subject to frost. Unripened shoots in the autumn and young growths in the spring are much more susceptible than ripened shoots and winter buds. Many trees are frost-ten-der when young, whilst at maturity they may be damaged only by severe frosts, e.g., pohutukawa. Within even a comparatively small area various factors influence the severity of frosts. On fairly steep slopes the cold air sinks down to lower levels, with the result that temperatures are higher on the slopes and lower in the valleys or flat areas. In the latter case the cold air may be dispersed by friendly air currents and this accounts for the oft-named frost-free valleys.

Sunny faces are warmer and growth is stimulated earlier in .the season and ripened thoroughly in the autumn. They are sheltered from the cold southerlies and in many cases from the early morning sun which may accentuate frost damage by the sudden thawing of frozen tissue. Houses and brick or stone walls which absorb the sun’s heat during the day keep air warmer in their vicinity. The close proximity of other tree and shrub growth makes warm pockets in addition to giving shelter. Records kept at the rose trial grounds at Massey College show that, on this sheltered terrace, the temperatures are approximately 4 degrees higher than those recorded on the flat areas below. Furthermore, this has been substantiated by the behaviour of tender and halfhardy plants growing on warm banks in the college grounds. There are several ways in which frost damage may be minimised. The older method of surrounding the base of the main stem with cinders or similar material is particularly suited for fuschias. If plants are totally covered early in the season, growth becomes drawn and soft and more than ever subject to frost damage. I prefer to protect the main stem and branches with bracken or manuka brush. If severe weather threatens subjects may be covered at night with scrim, or a permanent shelter of manuka or bracken should be provided. The latter applies particularly to evergreens, including tender ericas, tibouchina (lasiandra) and particularly early-flowering subjects such as luculia and jtamaderrie elliptic (Golden Tainui), which form their flower buds prior to winter. By far the greater number of half-hardy subjects which survive our frosts are those which flower in the autumn. These subjects, coming from warmer climates, should be given sunny positions in sheltered corners preferably in a deep welldrained, light to medium loam. i ' ' Choices For Autumn One of the most delightful of autumn-flowered subjects is lagerstroemia indica, the “crape myrtle.” There are various shades of pink and white flowered varieties. In coldest districts this plant may be frosted back to the base, and should be protected. This plant flowers when quite young and almost completely hides the foliage; it should be much better known. Hibiscus syriacus, “Rose of Gharon” is a quite hardy deciduous shrub and should be pruned in a similar manner to the above. The neriums “Oleander” are freeflowering late summer and autumn subjects. They prefer a well-drain-ed light loamy soil in full sun. The hybrid abutilons are well known to all, though the pink and cyclamen shades are less common. They need a sheltered corner in colder districts and, if becoming leggy, they should be pruned back in the spring. Lantanas are rather strong-grow-ing subjects, almost a weed in tropical climates. They are checked by frost in temperate climes and seedlings are seldom troublesome. The newer varieties are showy, freeflowering subjects in several bright colours and if cut back by frost or pruned in the spring they give abundant autumn colour. The “scarlet gum” (eucalyptus ficifolia) is well known for its brilliant display during February. The colours vary from scarlet to orange and flame and occasionally poorer colours as they are raised from seed. They are rather subject to frost damage when young but will stand fairly heavy frosts when older.