Gardening: When and why you should replace your garden seeds

Gardening: When and why you should replace your garden seeds

The viability of vegetables and flower seeds varies enormously. Use this handy guide to measure the durability of your seeds.

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In the deep, dark cold of winter, the garden season seems like a distant memory or wishful thinking. I have too many houseplants, so to satisfy my garden itch, I have decided that I finally need to clean up and organize my extensive flower and vegetable seed collection. I house seeds from many years and it’s time to clean up that mess!

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I am often asked, “How do you know if your vegetable or flower seeds are still viable? How long can I store my vegetable seeds? Should I buy new seeds this year?” Storage conditions and storage time vary for each vegetable and flower.Flower seeds generally last longer than most vegetable seeds.Some seeds are easily kept for up to five years, while others should be replaced annually.

As a general rule of thumb, high humidity and high temperature reduce the quality and viability of flower and vegetable seeds. This does not mean you have to invest in a dehumidification system for your “high-tech, airtight, temperature-controlled, underground seed storage unit.” For most seeds, storage temperatures between 5 and 10ºC are more than sufficient for at least one year of storage, as long as the seeds are dry and stored in dry conditions (airtight containers or plastic bags are sufficient).

Vegetables with a seed storage time of five years, in dry conditions with average to cool temperatures, include: cucumber, endive, lettuce, musk melon and radish. In the second extreme include some vegetables that should only be stored for one year: onions, parsley and parsnips.

Seed storage of sweet corn, leeks and okra should be limited to two years. The germination rate will decrease significantly after that time. A maximum of three years of seed storage for asparagus, beans, broccoli, carrots, celery, kohlrabi, peppers, spinach and peas is recommended. Beets, Brussels sprouts, cabbage, cauliflower, chard, eggplant, kale, pumpkin, squash, rutabaga, tomato and watermelon seeds should have good germination even after four years of storage.

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Flower viability varies enormously. For example, nasturtium and zinnia seeds can easily last up to 7 years, while pansy and impatience seeds can remain viable for only 1 or 2 years.

Although some of your seeds may be older than these recommended dates, there is no need to throw them out. Instead, do your own simple home germination test this winter. Take two pieces of paper towel. Place a piece of damp paper towel on a plate. Spread ten seeds on kitchen roll. Moisten the second paper towel and place it lightly over the seeds. Keep the paper towels slightly damp and place the plate in a warm place (20ºC), away from direct sunlight. After several days, check the seeds for germination. Some seeds germinate faster than others, so be patient. For example, the average germination time for radish and lettuce is four days at 20ºC, whereas beans can take up to 18 days to germinate at that temperature. If seeds are not germinated after 20 days, they probably will not.

By counting the number of seeds that have germinated, you can determine your germination percentage. For example, if 4 seeds out of the 10 are germinated, your germination capacity is 40%. This number is important when it comes to sowing time. A germination rate of 40% tells you that in order to have plants with the desired distance, you need to sow 2.5 seeds for each desired plant. Since half seeds do not grow very well, you will need to sow 3 seeds for each desired plant to ensure that you have a suitable plant stand. If all 3 seeds germinate, your hoe can easily take care of the extra plants.

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