You don't want to freeze them, as ice crystals can form killing cells in seeds. Some water in seeds is necessary, which means that freeze drying, aka freezer burn, can remove necessary water in seed cells, thereby killing them. Leave the freezing to experts with their liquid nitrogen and special tools that calibrate mineral and moisture contents for supercooling by using spin glass or transition state liquids. If that sentence made sense to you, it probably means your garden is in or at a seed research lab.
For the rest of us, it is important to know that not many seeds will last more than 10 years in normal room temperature storage. Many seeds won't last more than 5 years, but most will last 2-5 years. Refrigeration and controlled moisture can double these numbers. See the chart below for assessing the potential life span of those vegetable seeds stored in your desk drawer or seed box (at room temperature).
| Seed | Life in Years |
| Bean, Broad | 2 |
| Beet | 5 |
| Beet Spinach | 5 |
| Broccoli | 5 |
| Cabbage | 5 |
| Carrot | 3 |
| Cauliflower | 5 |
| Cucumber | 7 |
| Kale | 4 |
| Kohlrabi | 4 |
| Leek | 3 |
| Lettuce | 4 |
| Marrow | 6 |
| Courgette | 6 |
| Onion | 4 |
| Parsley | 2 |
| Parsnip | 1 |
| Peas | 2 |
| Radish | 4 |
| Salsify | 2 |
| Spinach | 2 |
| Tomato | 3 |
| Turnip | 2 |
Some seed varieties require different amounts of cold and moist storage temperatures--stratification--to become viable. This natural resistance gives seeds an edge when conditions are not favorable. However, if you're wanting to plant, say, milkweed, you're going to have very poor results without 180 days of cold moist treatment.
The basics of germinable seeds, however, are very simple: remove germination inhibitors and provide the seed with its preferred conditions of temperature and moisture. Most, if not all, seeds germinate at one of two temperature ranges: 38-42 degrees and 64-72 degrees. Some may be slightly one side or the other, but almost all fall close to these two temperatures.
Further, some seeds are highly vulnerable to viruses. Often you will see it recommended that these seeds be treated with near boiling water which kills viruses and bacteria that may be dormant. Others will have hard seed coats, and you will see treatments such as immersion in sulfuric acid or a requirement to file or nick the seed coat to remove the physical barrier that prevents moisture from entering and inhibitors from exiting.
When looking at wildflower seeds, it seems there are about as many treatments as there are kinds of seeds. Many seeds require leaching or exposure to a particular mold, producing a particular inhibitor removal plant hormone. Whatever the treatment, it is almost always for the purpose of removing an inhibitor or a pathogen. Providing that your seed is viable, using the proper treatment for your seed will save you time and money and increase your chances for success.
Online Resources
- Grassed up: Principles of native grass seed storage - New South Wales Department of Primary Industries
- Longevity of seeds in ideal storage - Hill Gardens of Maine
- Maintaining Seed Viability in Storage - Oregon State University, Seed Services Laboratory
- Personal Seed Bank - Johno's Garden Blog
- Proper Storage Important to Keeping Seeds Viable - Ohio State University Extension
- Seed Germination Database - Backyard Gardener
- Seed Saving for Beginners - FedCo Seeds
- Storing Vegetable and Flower Seeds - Colorado State University Extension
- Vegetables: Storing Vegetables and Seeds - Mississippi State University Extension
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