Someone told me they were getting ready to order all their seeds for this year's garden and I nearly fell off my chair.

All their seeds? There weren't any leftovers from last season? Do people really buy new seeds every year?

It's true that some seeds don't do well from one year to the other (onions are notorious for poor germination from one year to the next), but most vegetable and flower seeds can be viable for up to five years and some even longer. Weed seeds can seemingly live forever, lying dormant until conditions are right for germination. Weed conditions always seem to be right in my garden, but that's a topic for another time.

While many seed varieties can be stored from one season to another, it's important to note that as time passes, seeds will lose a certain percentage of germination. This means that while we may get 98 percent seed germination in a current year's package, the percentage of germination decreases each year. The rate of decrease is not the same for all plants and vegetables and in most cases, a bit of experimentation is needed to determine what that percentage is. Some people don't like to bother, but I think it's kind of fun to see what our seed packets have retained from year to year.

If you're a real seed geek, and I'm not naming names, you even can create a spreadsheet on your computer to really make it look scientific. This also is where learning those sixth-grade fractions come in handy.

I don't know about you, but when I order a packet of seeds, I usually get many more than I will ever use in one season. After I plant what I need, I fold down the top of the packet, put it in a plastic bag and put the bag inside a glass canning jar. At the end of planting, I put a lid on the jar and put it in the refrigerator where it stays cool and dry until next season. Now comes the fun part.

In winter, since there is no outdoor gardening to do, I pull out the jar of seeds and start figuring out percentages. I might do this in small planters, terrariums or even canning jars, or I might just use a paper plate and some wet paper towels.

Count out some seeds from one of the seed packets and plant them. It's important to remember how many are planted because these numbers will determine the rate of germination on those particular seeds. After the seeds germinate, count how many have sprouted. It's actually easier to do this on a damp paper towel because it is easier to see and count the sprouts, but it is also is a little more fussy since the paper towel has to be kept constantly moist.

After giving the seeds adequate time to germinate, usually a week to 10 days, it's time to start using the formula to get the germination percentage. This also is a good project to do with kids.

As an example, let's say I planted 20 heirloom tomato seeds that were newly collected from last season's plants. Of those 20 seeds, 18 germinated. I would write a fraction that was 18 over 20 (18/20). Then I would change the fraction to one with a denominator of 100. Since 20 times five is 100, multiply 18 times five to get 90. My new fraction is now 90/100. This tells me that 90 percent of my seeds are viable. It makes sense that the more seeds used the more accurate the results.

Whatever I don't plant this year will be saved for next year. In January 2013, once again I will plant some of the seeds to test their germination rate. Chances are the percentage of seeds that germinate from two year-old seeds will be smaller. To get an accurate germination rate, don't mix seeds collected one year with those collected in other years.

What is the reason for testing germination percentages? One reason is because it is fun to log each vegetable's percentage and see how the rates change from year to year. The main reason, however, is to tell me whether or not I need to buy new seeds. If 60 percent of my tomato seeds are viable, I know I will need to plant that row a little more thickly or that I need to sow enough seeds to ensure I will get enough plants for the garden.

It also tells me when it's time to toss the remaining seeds and start collecting a fresh batch.