|The first step is to soak the seeds in tap water. Every seed species is put in a plastic glass and recovered with water for 24-48 hours. Usually viable seeds will fall to the bottom of the glass within 24 hours at room temperature. Empty seeds will be floating (Pinus, Abies, Picea, Torreya, Taxus, etc.). It is easy to cut some seeds to verify; then the floating empty seeds can be discarded. On the photo on the right, bubbles are appearing at the surface of the seedcoats. It is the best evidence of fresh seeds chemical activity. The small bubbles are pulling some seeds upwards.|
Seeds just taken out of the refrigerator.
Two seeds are germinating.
18 January 2004
|Pre-treatment : when the seeds are fresh, usually no pre-treatment is required. Most fertile seeds will germinate without problem. When the frost period is over, begin to sow outside, allowing the seeds to be exposed to temperature variations between day and night. Some seeds will germinate better with low temperatures (below 20°C - especially Abies and Cedrus seeds). Some genera like Taxus and Juniperus can germinate already the first year, but more often or more regularly the second year. A better control of germination can be carried by a cold pre-treatment. It is also advisable for stored seeds. In that case I will recommand a nude stratification. This method will avoid as much as possible contamination by bacteria or fungi. After soaking the seeds in water, surface dry the seeds roughly and put them in a plastic zip-bag and in the refrigerator at a temperature below 5°C. A thin tube will allow gaz exchanges (avoiding an anaerobic confinement - see photo). Check every week for seeds beginning to germinate. When it is happening, take the seed out and sow it preferably at a temperature not below 20°C, in an acidic medium to avoid fungi (but no peat moss, please). Ungerminating seeds can stay in the refrigerator for several weeks or can be sowed right away after 3 or 4 weeks. This method (keeping the seeds in the refrigerator) is working fine with Cupressus, Juniperus (the later seeds germinating up to one year after being placed in the refrigerator). For the most difficult seeds, after a few weeks, take them out of the refrigerator, let them dry at room temperature for a few days. Then there is an alternative: to store them half-dry in the refrigerator again for a later use (if the growing season is over, for instance), or re-soak them and repeat the previous treatment. The Pinus sabiniana seeds on the photo had this very treatment after a few years of storage.|
Seed sowed in tube.
26 January 2004
28 January 2004
29 January 2004
1st February 2004
30 January 2004
31 January 2004
31 January 2004
4 February 2004
|The worst thing is to put a label when the inscription will be erased once submitted to sunlight, rain and variations of temperature. Very few labels will resist such treatment over time. One of the best and cheapest solution is to engrave one plastic label with a soldering-iron. The inscription will last for ever, insuring that the sowing and future seedlings will be always identified.|
| The sowing place is something worth considering. It is always better that the tubes or pots will not lay on the soil to avoid contamination by damping-off fungi. The design of this table has the purpose to protect the seeds from mice. These animals can easily smell seeds in the soil and dig them out to eat. You will know that your seeds were viable, but usually none will be left. The table is constituted of several boards placed upon a piling foundation (6 upright bricks, 40 cm high). This table is 3 meters long and 1.40 meters wide. It is covered with a plastic cloth to protect the wooden boards from the water. The green net in the foreground will protect the tubes from direct sunlight (keeping moisture) and also from the second main hazard for the seeds : birds. (Photo: March 2001)|
Second photo (April 2001) : final setting. Under the net about 1'600 tubes are awaiting germination of more than 40 different species of conifers.
|The choice of the material is very important. Many ornamental nurseries are using small pots to avoid using a lot of medium and to save place. Often the roots will be spiralling at the bottom of the pot and the result will be roots not fit to anchor well the future tree in the soil. The Keteleeria davidiana on the photo is even likely to strangle itself while growing... The roots were not spiralling at the bottom of the pot : the mess shown on the photo is the consequence of the use of a very small pot for a too long time, the plant being fed artificially. It is for this very reason that the Arboretum de Villardebelle is growing most seedlings in its own nursery using forestry material.|
When the germination occurs, the root is the first to emerge out of the seedcoat. This quite young Pseudotsuga macrocarpa seedling on the left is a very good example of the importance of the root before the seedling will emerge from the surface of the soil. The root is already 11cm long while the aerial part is only 3 cm high and the cotyledons are still not completely out of the seedcoat. In a small pot, the root will begin to grow horizontally and to spiral at this early stage.
The best material is used by forest nurseries : tubes allowing air-pruning at their bottom. Here is (photos below) the result with a Pinus koraiensis grown already for 5 years in a plastic tube. The medium is composted pine bark. The roots are colonized by a mycorrhizal fungus (whitish on the photo). The roots are well formed and there should be no problem at planting time, nor in the future.
| The example shown on the picture is a multipot with 45 tubes. It will allow seedlings to grow for 1 year (fast growing conifers like Metasequoia, Cryptomeria, Cupressus, many Pinus species, etc.) or for 2 years (slow growing conifers like most Abies, Picea, Taxus, Juniperus and some Pinus species − aristata, balfouriana, longaeva).
The photo shows 1 year old Cupressus abramsiana seedlings in the process of being repotted.
| After one or two years − depending on the size of the plants − the seedlings are carefully retrieved from the multipots and repotted in larger tubes (here
Deepots40). They are 25 cm deep (10 inches), allowing the roots to grow further down. The tubes are displayed on a tray with 20 places.
These pots are also used to sow large seeds like Torreya or Pinus maximartinezii and Pinus torreyana.
Some Cupressus abramsiana after repotting.
| On the right of the picture a typical protection for seedlings. Held by 3 (sometimes 4 for bigger plants) stakes, a chicken-wire fence is protecting efficiently the seedling. The fence is one meter high and will keep away sheep, deer and wild boar (although sometimes the fence is pushed and completely deformed, but without harm to the small plant). Wild boars will uproot the freshly planted unprotected seedlings or bark the trunk of a tree. The seedling inside the fence is an Abies concolor.|
On the left of the picture is a 220 liters barrel to collect rain. The water will be used at the time of planting or in case of drought during the first year. With caution in this case, for mice will quite often be attracted by moisture and will begin to dig galleries under the seedling.
| The second type of protection is a black plastic net, like a tube, 1.20 meter high and 30 cm of diameter. This device fixed on a wood stake and hold straight with one or two metallic stakes does not only insure a protection against animals, but also against direct sunlight and wind. A microclimate will develop in the middle of the net. The result will be more healthy plants, as it became obvious looking at seedlings of the same species planted close to each other, one under the black net, the second surrounded by a chicken-wire fence. The leaves will be darker green (Abies numidica, Picea orientalis).|
On the picture, a small Pinus edulis seedling is to be seen through the net (look at the enlarged picture by clicking on the photo).
Text & Photos : © Arboretum de Villardebelle