Drying racks are provided in Terraformation seed banks, and this is also something you could easily set up yourself. Any kind of rack system or shelving that allows for shallow trays with good airflow could be used for this purpose. To use the racks, simply spread the seeds out in a single layer in one or more trays, with only one seed accession per tray. It is critical that seeds are in a single layer, so that all the seeds dry evenly. Otherwise, seeds underneath other seeds will retain more moisture. For a Terraformation seed bank kept at 35%–40% RH, these racks can be used to dry seeds for frozen storage.Electronic drying cabinets (which may also be called dry cabinets, electronic humidity control chambers, desiccation chambers, or similar names) allow a user to control the internal relative humidity.
Terraformation seed banks are equipped with four drying cabinets. These are relatively inexpensive and sufficient for restoration seed banking. We recommend setting three cabinets to 30% RH and the last one to 40% RH. You can use the cabinets at 30% to dry seeds for refrigerated storage at 5°C, and the cabinet at 40% to dry small seeds for frozen storage at –20°C. Of course, you can also adjust the cabinets for your seed bank’s needs. As with the drying racks, spread the seeds out in a tray appropriate to the size of the seed accession.
One other useful option for seeds that will be refrigerated is to dry them on drying racks for a while, then move them to the drying cabinets to reach 30% relative humidity.Other OptionsIn addition to drying tools provided in Terraformation seed banks, there are also a variety of non-electronic dry boxes, often made of clear acrylic material for viewing internal contents, with hermetically sealing doors. This can work quite well as a low-tech option with no power required for the drying unit itself. However, these dry boxes will require some type of desiccant inside in order to dry the seeds, and the desiccant will also need to be recharged, which will require some use of power.Some dry boxes have corresponding silica gel desiccant cartridges, in which case, it is good to have several of these cartridges on hand, because it is likely that seed drying will require frequent cycling/recharging.
You would also need to have an oven available to recharge the cartridges using low heat.As a cheaper alternative, you may be able to purchase silica gel beads in bulk (not in a cartridge) and simply place them in a tray inside the dry box to do the desiccation work. They will still need to be regularly recharged by spreading them out on a tray in an oven on low heat.Important note on silica gel: Color indicating silica gel beads are important, so that you can visually tell when the silica gel has become saturated with moisture and is no longer able to dry the air and the seeds inside the box. However, we recommend not to use blue-to-pink color indicator beads, because these contain a chemical that is a carcinogen if the beads are broken into particles that can be inhaled. Blue-to-pink beads can be ok contained inside a cartridge, since this would avoid breakage, but we don't recommend using them in the open, especially if they are handled over and over again in recharging.
Instead, orange-to-green color indicating silica gel beads are a safe alternative. They are recharged in the same way but do not contain hazardous chemicals. Since color indicating silica gel is more expensive than regular white silica gel, one option is to buy both types, mixing in some color-indicating with the regular white silica gel (they should all need to be recharged around the same time).Finally, in some places in the world, you can purchase mini-dehumidifier units that contain silica gel inside and can be recharged simply by plugging the unit into a standard electrical outlet. These are convenient, and a seed bank could purchase enough of them to keep recharging and cycling through their non-electronic dry boxes. With a larger box full of fresh seeds, they may need to be recharged every week or few days. However, drying seeds on drying racks first, then moving partially-dried seeds to cabinets would reduce the frequency of recharging any of the options above (essentially using dry boxes for fine-tuning and for collections of very small seeds).
Terraformation seed banks are equipped with four drying cabinets. These are relatively inexpensive and sufficient for restoration seed banking. We recommend setting three cabinets to 30% RH and the last one to 40% RH. You can use the cabinets at 30% to dry seeds for refrigerated storage at 5°C, and the cabinet at 40% to dry small seeds for frozen storage at –20°C. Of course, you can also adjust the cabinets for your seed bank’s needs. As with the drying racks, spread the seeds out in a tray appropriate to the size of the seed accession.
One other useful option for seeds that will be refrigerated is to dry them on drying racks for a while, then move them to the drying cabinets to reach 30% relative humidity.Other OptionsIn addition to drying tools provided in Terraformation seed banks, there are also a variety of non-electronic dry boxes, often made of clear acrylic material for viewing internal contents, with hermetically sealing doors. This can work quite well as a low-tech option with no power required for the drying unit itself. However, these dry boxes will require some type of desiccant inside in order to dry the seeds, and the desiccant will also need to be recharged, which will require some use of power.Some dry boxes have corresponding silica gel desiccant cartridges, in which case, it is good to have several of these cartridges on hand, because it is likely that seed drying will require frequent cycling/recharging.
You would also need to have an oven available to recharge the cartridges using low heat.As a cheaper alternative, you may be able to purchase silica gel beads in bulk (not in a cartridge) and simply place them in a tray inside the dry box to do the desiccation work. They will still need to be regularly recharged by spreading them out on a tray in an oven on low heat.Important note on silica gel: Color indicating silica gel beads are important, so that you can visually tell when the silica gel has become saturated with moisture and is no longer able to dry the air and the seeds inside the box. However, we recommend not to use blue-to-pink color indicator beads, because these contain a chemical that is a carcinogen if the beads are broken into particles that can be inhaled. Blue-to-pink beads can be ok contained inside a cartridge, since this would avoid breakage, but we don't recommend using them in the open, especially if they are handled over and over again in recharging.
Instead, orange-to-green color indicating silica gel beads are a safe alternative. They are recharged in the same way but do not contain hazardous chemicals. Since color indicating silica gel is more expensive than regular white silica gel, one option is to buy both types, mixing in some color-indicating with the regular white silica gel (they should all need to be recharged around the same time).Finally, in some places in the world, you can purchase mini-dehumidifier units that contain silica gel inside and can be recharged simply by plugging the unit into a standard electrical outlet. These are convenient, and a seed bank could purchase enough of them to keep recharging and cycling through their non-electronic dry boxes. With a larger box full of fresh seeds, they may need to be recharged every week or few days. However, drying seeds on drying racks first, then moving partially-dried seeds to cabinets would reduce the frequency of recharging any of the options above (essentially using dry boxes for fine-tuning and for collections of very small seeds).
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