Plant propagation - Principles of Horticulture - page 136

Figure 11.11 Mist propagation unit Figure 11.12 Hardwood cuttings

plants, keep in polythene bags and use as quickly as
possible.
The area of leaf on these cuttings should be kept to a
minimum to reduce water loss. Misting (spraying the
plants with fine droplets of water to increase humidity
and reduce temperature) can further reduce this risk
by slowing down the transpiration rate. Automatic
misting (Figure 11.11) employs a switch attached to
a sensitive device that assesses the evaporation rate
from the leaves.
For plants such as Chrysathemum spp. it is often
better for amateurs and small growers with limited
propagation space to obtain rooted cuttings from
specialist propagators because then all that is required
is an area of reduced light where high humidity
(misting) can be maintained for 2-3 days until root
growth begins. If they cannot be 'stuck' immediately,
the cuttings can be stored in a refrigerator (at 1-5°C)
for several days.
Leaf cuttings include leaf lamina and leaf petiole
cuttings. There are several ways by which leaf
lamina cuttings may be taken. One method suitable
for Begonia rex is to take whole leaves or just small
squares of the leaf and pin down so the veins make
good contact with a free-draining compost in a tray,
keeping them humid and at 20°C; plantlets develop
along the length of the veins in 6-8 weeks. A similar
method is used for Streptocarpus cvs but the whole

leaf is split along the midrib, which is removed, and
the cut edges are inserted into trays of compost.
Leaf petiole cuttings are taken from Peperomia spp.,
using mature leaves, and Saintpaulia cvs, with full-
grown young leaves, with 5 cm of leaf stalk. This is
inserted into the compost; rooted plantlets can be
detached from the petioles after about eight weeks.
Semi-ripe cuttings are taken from stems that are
just becoming woody (partially mature wood of the
current season's growth); typically, in mid-summer to
early autumn. They are used for many broadleaved
evergreen shrubs and some conifers such as
Chamaecyparis spp. These cuttings should be 5-10 cm
long with the base firm but the tip soft active growth.
Rooting in a sand/compost mixture may be achieved
in cold frames or, more quickly, in a heated structure
at about 18°C. Some species such as Elaeagnus spp.
(oleaster) will root only if heat is provided.
Heeled cuttings are preferred for many shrub and
tree species (e.g. Ceanothus , holly and conifers), by
which the semi-ripe cutting is taken in such a way that
about a centimetre sliver of the previous year's wood,
the heel , is still attached. The heel cambium facilitates
root formation and, hence, easier establishment.
However, it is a method which is not attractive for
commercial production because it removes basal buds
from the mother plant and in so doing prevents any
future regrowth.