Horticulture Principles and Practices

Temperature
320 Chapter 10 Asexual Propagation
Bottom heat in cutting beds warms the soil to induce quicker rooting. It is important to
have adequate rooting before the shoot starts to grow vigorously. The bottom heat is usually
about 6°C (10°F) higher than the air temperature, which should be maintained
between 18 and 27°C (65 and 75°F). Supplement heating is critical during cold periods
to avoid injury.
Moisture and Humidity
Intermittent mist and fog system, controlled by a timing device, are commonly used for
propagation. The misting frequency and duration depend on light, radiation, and air temperature.
Cuttings do not have roots and hence are unable to absorb moisture. However,
the exposed plant parts are subject to evaporation. To reduce moisture loss, cuttings are
generally maintained under conditions of high moisture by misting them. Initially,
misting may be required almost continuously. As time goes by, the misting schedule is
modified, being less frequent and less intense. In some greenhouses, a mist is replaced
by a fog.
Nutrition
No fertilization is needed for unrooted cuttings since they can take up very little of it.
Light fertilization may be applied through the mist. Once rooted, a complete
fertilizer application of 20:20:20, for example, at a rate of 1 pound (0.45 kilogram) per
100 gallons (378.5 liters) of water may be applied.
Rooting Medium
Certain species, including coleus, African violet, and Philodendron scandens, can root
in water alone. Most cuttings are rooted in solid media that must be sterilized, freely
draining, and of good moisture-holding capacity. Sand is well drained but poor in
moisture-holding capacity. If sand is used, the rooting should be conducted under
shady conditions and should be hand watered. Vermiculite and perlite make good propagation
media, especially when combined with peat most. The medium for propagation
must be very loose to enable rooted cuttings to be readily removed from the
rooting medium and planted with little loss of roots. Propagation may also be conducted
in outdoor conditions, provided the medium is well drained and aerated to avoid
saturated water conditions.
In place of the conventional rooting media, a variety of preformed, lightweight
materials are widely used. These media include rockwool media, compressed peat pellets,
and other artificial materials marketed under various brand names such as Oasis root
cube, Oasis wedge, and Horticubes. Sometimes cuttings are rooted directly in the finish
pots. Species such as geranium and poinsettia are propagated in this way.
Sanitation
Cuttings have exposed surfaces and hence are prone to disease attack. The propagating
medium must be sterilized before use. Steam sterilization is effective in controlling most
soilborne diseases.
10.6.3 TAKING AND PREPARING CUTTINGS
Select the material according to age and size. Cuttings from plant parts that receive
optimal sunlight are most desirable. If cuttings are obtained from stocks in the field, they
should be wrapped in moist burlap or other suitable material to reduce water stress, and
be kept out of sunlight as well. If cuttings will not be prepared right away, the material
should be stored in a fridge or a cool place, or misted.