Best Practices for Long Term Seed Storage
As growers, we map out our season in late fall and early winter and, by the time planting season rolls around, things can change. From one season to the next, we may find ourselves holding onto more seeds than we are able to get into the ground. Some farmers and gardeners have even had to cancel their growing seasons all together due to water restrictions placed in regions enduring drought.
Here at High Mowing, we know how important it is to preserve the quality of your stored organic seeds. Keeping your seeds viable for future seasons is an easy way to ensure that what didn’t make it into the soil this year, will bring healthy harvests in the future. Below we will go over best practices for long term seed storage.
It is good to remember that seeds are nature's storage vessel of choice and, if stowed properly, seeds can often times be saved for use in more than one growing season. When it comes to thinking about storing your seeds, you should think about what conditions create and maintain the dormant state of the seed. Some of the most important conditions to control are temperature, light and moisture. All three of these environmental factors can spur the sprouting or even decay of your seeds.
Seeds should be stored in air tight containers. This can be achieved in a lot of different ways, but the idea is to protect the seeds from unwanted moisture, light and pests that may try and take up residence among your nutrient rich seeds. Mason jars are a great option for storing seeds that are loose or even storing seed packets. Seed packets can also be organized in plastic, sealable bags and then be stowed away in a Tupperware or other plastic or metal container. If humidity or moisture is a problem where you're located, placing silica gel packets can help manage excess moisture. These little packets are sold online and are similar to what you may find in a pair of shoes or garment that has been shipped. They are reusable, season after season.
One of the cues that seeds use to germinate is temperature. Different temperatures will cue different seeds, but as a rule, storing your seeds at 40 degrees Fahrenheit (or lower) is optimal. This can be difficult to achieve and is one reason why some growers choose to store their seeds in the freezer. This generally ensures that your seed remains dormant and is an easy way to store seeds for long periods of time. The problem with freezer storage is that, if you lose power, you may end up freezing and thawing your seeds which can result in decay. If you have a chest freezer, dedicating a lot of space to your seeds can be useful. If all you have is a residential freezer attached to your fridge, it may be best to pick just your favorite varieties for this space. Once the seeds have frozen in the freezer inside their airtight containers, it is important when you remove them from the freezer to let them reach room temperature before opening your containers. This makes sure that the seeds don't absorb the moisture generated from the thawing process which can impact their viability.
Storing seeds in the refrigerator can be tricky due to moisture and temperature fluctuations, but is similarly successful in preserving quality. Once again, when removing airtight containers from the fridge, it is important to let the containers reach room temperature before opening them.
If you cannot store your seeds somewhere that is around the optimal 40 degrees Fahrenheit, storing seeds in a cool, dark place that stays below 55-60 degrees Fahrenheit will work sufficiently well for many seed types, for a shorter amount of time. In this scenario, it is most important to maintain a constant temperature. Fluctuations in temperature can imitate changing seasons which can prematurely cue your seeds to start developing. Once a seed responds to environmental factors and starts organizing proteins in preparation for sprouting, it cannot re-enter a dormant state. This can lead to unwanted decay and loss in germination rates in your stored seeds.
As you know, watering your seeds in is the first step when starting crops. Moisture is essential in the sprouting process and is one of the most important cues for seeds that it is time to start growing. Managing moisture is very important when creating systems for long term seed storage. Once you've found a way to keep your seeds cool, you'll need to find a way to keep them dry. Mason jars and other glass containers are great options for seed storage so long as they are sealable. Ziplock bags, freezer bags and other plastic containers are also great options. If you are planning on keeping your seeds in their paper envelopes for organization, it is especially important to keep them dry as the paper of the envelope can absorb water and impart that to the seeds. When putting seeds or seed packets into plastic bags, it is very important to try and remove as much air as possible and double check to be sure there's no moisture trapped in the bag before sealing it.
Cold environments that are optimal for dormancy in seeds are usually environments that cause water to condense. That is why an airtight container is so important and also why allowing the containers to reach room temperature before opening them is essential. Using silica gel packets, powdered milk, or rice inside your storage vessels to trap moisture that may have made its way into your containers is an extra layer of protection against failed dormancy and decay.
For the same reason you don't store your bag of potatoes in a well lit place, you should not store your seeds in one. Light is another important cue to the seed that it is time to sprout. When storing your seeds in see-through glass and plastic containers, it is important to put these containers in a dark, dry place. This can be inside of another container with solid, opaque walls, in a cabinet, and/or stored beneath other things that block out the light. Sunlight is especially important to keep off of your seeds as the rays can not only spur sprouting, but can result in the natural decay of organic matter, the same way sunlight can result in the spoiling of food.
Seeds are not only stored potential and future plants, they are also food. Pests that bother seeds can come in many different shapes and sizes. Some of the worst pests for stored seeds are rodents and insects. Rodents, such as rats and mice, are notorious for eating stored grains and seeds. They will invade your pantry, barn, and other outbuildings. If you have difficulties with rodent pests, as most farms do, it is very important to ensure that your seeds are sealed into something rodent proof. This can be a sealable Tupperware or plastic container, a metal trashcan, or other container that will not succumb to the nibbling of tiny, sharp and persistent teeth.
Insect pests can be especially devastating because the damage may not be obvious until it is too late. Some common pests that invade stored seeds include beetles, weevils, borers and moths. The best method for dealing with insect pests, much like rodent pests, is prevention. One way to ensure that your stored seed does not get invaded by pests is to inspect your seeds before storage to make sure you don't have any stowaways. If you do happen to find an insect infestation in some of your seeds, the next step is to re-seal that container and put it in the freezer for 2 days. This will kill the infestation and not allow it to spread. Another useful method for preventing destruction of your seeds by insect pests is to limit the oxygen in the storage container. Insects need oxygen to survive and tightly sealed containers with limited extra space in them will help reduce the livable environment for the pests. If you happen to have a vacuum sealer, it is a great way to store seeds and reduce insect pest damage, so long as the seeds are dry.
While seeds can keep the dormant, embryonic plants inside of them viable for extended periods of time, they are made of organic materials and will naturally break down. Even when you are able to keep your seeds in a state of true dormancy, where the embryonic plant stays static and does not start processing the food (also known as the endosperm,) inside of the seed coat, the endosperm itself will eventually break down. This breakdown period differs for each crop type. Meaning, that even with optimal conditions, seed loss can occur over time and the rate at which this happens is different for each crop type.
Below we will highlight the average storage viability of each crop type.
- Sweet Corn
- Brussels Sprouts
- Mustard Greens
Even in optimal conditions, the gradual breakdown of your seed stock is inevitable and something to think about when pulling out your seeds for the next growing season. When pulling out your seeds from long term storage, it can be good practice to perform a germination test. For more information on checking on your seed's viability, check out our blog post: How To Do A Quick Germination Test At Home.