Section 3
Root Development
Root development is a very critical aspect of field performance of seedlings.
Effects of malformed or weakened root systems that result from spiralling of
roots or excessive growth in small-volume peat pot containers might not show
up for years after many thousands of hectares have been planted with container-grown
seedlings. Peat pot container plantings in the '70s led to blowdown of some areas
in the '90s.
Today's styroblock containers with their ribs do an excellent job of preventing
root spiralling and root binding. In fact, plug-mold systems were developed
because root growth of seedlings outplanted in rigid plastic tubes was impeded.
Ribs or grooves were added later in plug-mold sidewalls to direct root growth downward.
One major problem with container grown stock is that the great majority of the
regenerating roots are concentrated at the bottom of the container. This is particularly
unfavorable if the seedlings are to be planted in cold soils, since the low temperatures
at depths corresponding to the length of a container (ca 13-15 cm) will inhibit root
growth and result in severe planting check.
Laccaria laccata
A discussion of root development in containerized seedlings can not leave out the development of mycorrhizae. Mycorrhizal fungi form a symbiotic relationship with the root. Mycorrhizae means literally "fungus root". In container operations seedlings can become mycorrhizal in one of several ways. Spores of mycorrhizal fungi can be purchased and fed into the irrigation water. Spores can get occur naturally in the irrigation water if it comes from a stream. Mycorrhizal innoculum can be grown and placed into the growing media.
We will discuss later in the term how improper planting practices cause bare-root
stock to develop malformed roots and to make poor growth. So far no serious root
form problems with properly grown and planted plugs have been reported, except as
noted above for lodgepole, but until we have growth and survival data from plantations
for at least 20 years after planting, we may not be able to evaluate accurately the
effects of the container upon subsequent seedling growth.