Seeds are relatively quick to
plant compared to cuttings.
Collecting seeds: As with cuttings,
seeds should be collected from a plant that is healthy and has favourable
characteristics such as a good yield and visual appeal. Seeds should be
collected when mature. Seeds that are immature will not germinate when
planted. Immature seeds are soft and generally paler in color compared with
mature seeds of the same plant species.
Seed storage: It is important to realize
that a seed is a living organism. To suppress germination but maintain the
seed in a dormant state during storage, a cool, dark and dry environment is
needed. A screw topped glass jar stored in a refrigerator is ideal.
Procedure for producing seedlings
Medium: The choice of
growing medium is essential. It
should provide high oxygen and water levels and good drainage.
Disease: Seeds should be sterilized
prior to planting. Treatment methods include:
- Soaking seeds in hot water (50OC ±
1OC / 122OF ± 1.8OF) for ~25 minutes. With
this method, note the seed has a low tolerance to temperature error.
in 1% chlorine* solution for 5-10 minutes. Unlike the heat treatment method
mentioned above, chlorine only sterilizes the external surface of the seed.
Sterilization of hardware and media before and
during the propagation process is paramount.
*1 part household (50g/L) chlorine bleach + 4
Step 1. Thoroughly wash and sterilize
all hardware and areas that are likely to come in contact with the seedlings
and possibly cause disease.
Step 2. To increase the success rate of
seedlings, use a ‘heat mat’ and ‘propagation lid’ (Fig 17.4). The vents on
the propagation lid need to be closed. Maintain root and air temperature at
20-25OC (68-77OF) and relative humidity at ~80%. Note
that cool conditions delay the germination of most seeds. This extends the
length of time during which they are susceptible to fungal attack.
Step 3. Pre-soak the growing medium
(e.g. Rockwool) by immersing or drenching with a pH buffered
seedling nutrient solution. This will
help remove any excess ‘alkalinity’ that is often present in the material
and ensure the medium is bedded down. Allow excess nutrient to drain. If
using Rockwool, gently squeeze to remove the excess nutrient.
Pre-germinating the seeds prior to planting them in the medium can be
beneficial because it can help identify the better quality seedlings. To do
this, place the seeds between moist tissue paper on a plate. Cover this with
an up-turned plate to keep the seeds in the dark. Check every few days,
ensuring that the tissue does not become dry – sprinkle with water as
necessary. Once the root or “radical” becomes exposed, place the seed in the
medium in an upright position with the root pointing downwards. Locate ~2 to
5mm (1/8 inch) below the surface.
2. Sow the seeds at a depth equal to 2-3 times their diameter.
Cover the seeds with medium and gently press down.
Step 5. Immediately after planting, lightly re-water using water or bloom
nutrient solution at EC ~0.8mS (typically about one-third the normal
strength). Continue to water the medium as required, typically every 2 or 3
days. Ensure to maintain root and air temperature at 20-25OC
(68-77OF) and relative humidity at ~80%. Diligently remove any
dead leaves or seedlings - these are an ideal host for fungi.
Note: Some plant varieties or media may require
little or no nutrient until the first few 'true' leaves appear (Fig 17.7b).
If the success rate is poor, try feeding with plain water.
Step 6. Remove the ‘propagation lid’
once the first shoot appears (Fig 17.7a). This will help prevent fungal
Step 7. Light is not required during the
actual germination process. Once the first shoot (‘plumule’) appears
however, the seedlings need good light to begin photosynthesizing. This
prevents the plumule from becoming spindly or ‘etiolating’. Use low
intensity lighting for the first few weeks of growth. “Cool white”
fluorescent lights are preferable.
Position these ~10cm (4 inches) above the plants.
If seedlings are being grown outdoors, position
them in a partly shaded location. Too much light can stress seedlings in the
Step 8. Gradually expose the seedlings
to their proposed environment. Depending on the plant variety, this may take
only a few days, or many months. Begin to expose the seedlings to increased
light intensity and nutrient strength (see
Table 11.30). Ensure these changes are gradual as a sudden change might
Step 9. Healthy seedlings can grow
quickly, therefore it is essential to
transplant them into a bigger system
or container that provides adequate room for further root and shoot growth.
Do this only after a minimum of 2 ‘true leaves’ have formed (Fig 17.7b).