Treatment of Bare Rooted Rhododendrons
By Alleyne Cook, Vancouver, B.C.
The following method of treating rhododendrons imported from England has been used with understandable success by several New Zealanders. It should be remembered when reading what follows that there are certain differences between the two countries and the U.S. treatment would have to be modified.
The rhododendrons entering New Zealand have to be bare rooted, just as they do when entering the U.S. or Canada, they do not however have to be fried and frizzled as is the custom of the U.S. Department of Agriculture. They remain in quarantine for one year during which time they are inspected for disease by an inspector of the N. Z. Department of Agriculture.
Secondly the seasons are completely opposite, when it is spring in the U.S. it is autumn in N. Z. so regardless of what time of the year plants arrive it is always a considerable time before they have adjusted themselves to the changed seasons. Plants are nearly always sent during the English autumn arriving in a matter of days if sent by air, or some six to eight weeks later in the early summer if sent by boat. The plants which would normally be dormant for the next six months have to start into growth immediately and because they are later in doing this than plants already in N. Z. they are usually very soft when the winter starts and have to be carefully protected. The following spring finds them back to normal.
This is the method used. A trench is dug preferably on a slope, always in full sun. To give extra warmth under the plants the lower section of the trench is filled with hewn chippings, weeds, etc. A layer of soil is added then the plants are set in, their tops leaning uphill. To keep the leaves of the plants from losing moisture they are enclosed in polyethylene bags the ends of which are below the soil level. This treatment means that no part of the plant is exposed to the air, although they are not without it for polythene breathes while retaining the moisture. It has been found that under these conditions the leaves are very liable to sun scorch and at least three layers of burlap should cover them. The leaves are now completely covered but the sun can beat down on the soil covering the roots. It has been found that new roots start in three weeks and even the slowest plants have started within six weeks. When the new roots have made some growth the plants are hardened off gradually by opening the bags a little and increasing this opening every day.
It is quite probable that the New Zealanders using the above method have no glasshouses with heated benches. They would probably respond equally well to bottom heat which would be on at a controlled temperature both day and night and would therefore root even faster.