1. The cold store facility should be well controlled so that the desired temperature is maintained with little or no fluctuations. Marked fluctuations (3+°F.) can function as a pump to pull moisture out from the seedlings.
It has long been considered that cold storage is not damaging to coniferous seedlings. In reality, such treatment does represent a stress which may be either minor if it occurs during the period between December and March l or very major if it is initiated prior to early December or after the buds start swelling in the spring. Table X demonstrates that the adverse effect of cold storage upon the vigor of seedlings lifted in the fall is mediated in part through the root system. The same effect does not occur, however, with winter-lifted seedlings. Why? What temperature is the nursery soil likely to be in the fall? In the winter? How does the fact that roots do not withstand rapid changes in temperature relate to the fact that moving them from the soil to the cold room in the fall is a more stressful operation than it is in the winter?
A second interpretation of the data in Table X is that the seedlings require some daily change in their environment to maintain their vigor (circadian rhythm). Again, however, this effect is not present in winterlifted stock.
| Treatment | ||||
|---|---|---|---|---|
| Cold roots | Warm roots | |||
| Response | ht* | rk* | ht* | rk* |
| 2 | 8 | 0 | 4 | |
| 6 | 8 | 0 | 45 | |
| 0 | 9 | 6 | -7 | |
1. The cold store facility should be well controlled so that the desired temperature is maintained with little or no fluctuations. Marked fluctuations (3+°F.) can function as a pump to pull moisture out from the seedlings.
2. Seedlings should be stored moist, but not sloppy wet. Seedling roots should be relatively clean. Packing material around roots, such as peat moss, does not generally increase seedling vigor over those packed bare root, but does provide a measure of insurance against excessive drying in the field if care is not taken to maintain the seedling containers closed and in the shade during the planting operation.
3. Seedlings lifted early (i.e., in November)1 should never be stored more than a few days. Damage caused by such storage may be reduced by storing seedlings at 45°F. instead of the more common 35°F. However, such practice is not recommended for storage periods of more than a week as it is more conducive to mold development.
4. Seedlings which are to be stored during the spring months preparatory to outplanting in high elevation areas should be lifted in mid-to late-February rather than after the buds swell.
5. Containers of seedlings should be spaced in the cold store facility to permit free movement of air around them. Failure to do so may result in gradual heating of the seedlings as a result of the heat of respiration.
6. Trials with Douglas-fir strongly suggest storage periods of no more than two weeks at temperatures above 40°F or the result is a decline of seedling vigor.
Recent work has shown that seedlings may be stored for several months successfully at temperatures just below freezing ("Freezer Storage"). Such a technique is, however, expensive and requires careful handling of the stock both before and after the storage period. Further, the stock must be thoroughly dormant at time of storage. This technique appears to be most favorable, relative to above freezing storage, for storage period of several months duration, and is, therefore, most commonly used for storage of stock to be planted in the interior of British Columbia. Such seedlings are commonly lifted from nurseries in the lower mainland in mid to late winter and stored until areas to be planted are free of frost in late spring. One major advantage of below freezing storage is that these temperatures completely inhibit the growth of fungi.
It should be recognized that, although much of the moisture within seedlings does not freeze at -2°C because the cell sap has sufficient osmotic potential to reduce the freezing point several degrees, frozen seedlings may be easily damaged. When they are removed from the freezer, they should be thawed gradually in a cool room before shipment. Logistics which result in thawing frozen seedlings by placing them in a creek immediately before planting are not compatible with a high survival potential for the treated seedlings.
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