Last month I started getting ready for the new planting season. We’re pretty lucky here in Arizona, things get started pretty early and I wasn’t going to waste a minute of potential growing time. I did maintenance on all the planting beds, added new compost and soil conditioners, added new mulch and cleaned out any old material that would be in the way. I took inventory of my seed collection and poured over catalogs ordering new seed I knew I wanted to try this year. I felt like I had a pretty solid start to the early season.
I started some seeds under the new grow light setup, but others were broadcast by hand directly into the planters. After a week or so, sprouts were popping up all over the place…except for one planter. My largest raised planter was not showing any sprouts. I waited a little longer, but while all the other planters were showing great progress and healthy sprouts were popping up everywhere the big planter was showing next to nothing. I realized that I had broadcast some old seed in that particular planter. So in an effort to troubleshoot the problem, I decided to test the germination rate of the older seeds I had sown there.
The process to test the germination rate of your old seed packets is not that difficult, it just takes a little time and some basic supplies that most people have around the house.
Testing Your Old Seed
What You’ll Need
Wet the paper towel in the water. Not too wet, but moist enough to create a good environment for the seeds to sprout. If you live in the city you might want to avoid using tap water because it may have chemicals that could inhibit seed sprouting. I used water from my rain harvest.
Fold the paper towel in half and lay flat, select 10 seeds from your test pack and space them evenly on one half of the paper towel. Give them room, seeds should not be touching.
Fold the paper towel over to enclose the seed, press lightly to make sure the seeds are sandwiched firmly between the wet towel halves.
Place the paper towel with the seeds in a plastic sandwich bag and label the bag with the plant variety and date.
Set the plastic bag in a warm place out of direct sunlight. Some seeds need a little sunlight to germinate, so you don’t need to set it in the dark just out of direct sunlight.
Every three days or so you should check the seed for germination and moisture. Add a little water if necessary to keep the towel moist.
The seed packet may give you an estimated germination period for your seed. If not, you can find an estimate online. After the estimated germination period, count how many seeds have sprouted. Your germination rate can easily be calculated from this test (10% per successful sprout i.e. 5 out of 10 equals 50%). This will show you if your seed is viable, or at least how much the germination rate has dropped on older seed. Testing our seed this way before planting is a good way to determine how much seed to sow or whether or not you should just order new seed.
This is especially handy if you are saving seed and need to test your own germination rates.
If your germination rate is low, say 50% or less, but you still want to use the seed, it would probably be a good idea to pre-sprout your seed before planting so that you know you are only planting seed that successfully germinated. Watch the sprouts though, older seed can produce weaker plants and that’s no good to anyone. If the sprouts are struggling or don’t develop properly, scrap them and just get new seed.
Result- In my case, I was testing spinach seed that had failed when direct sowed into the planters. The seed I tested germinated quickly, some beginning to sprout within the first day. After 4 days I had 4 fully sprouted seeds and 1 that was barely starting and 5 that were not showing signs of doing anything. 40%-50% successful germination rate. Pretty sad. It looks like I will be ordering new seed this year for spinach.
BONUS: Seed Storage
Keep your seed alive by storing it properly! Humidity and heat are the enemies of seed longevity. Humidity causes the quickest deterioration. Ideal moisture content for most seed is no more than 10-12% so store at low relative humidity. Optimum storage is in a sealed jar in a freezer or refrigerator. Failing that, the sum of temperature plus relative humidity where seed is kept should never exceed 100.
• Never store seed in a humid, warm or sunny spot.
• Don’t ever leave it in a greenhouse or hoophouse for even a few hours.
Most seed stored properly will last for several years. A few seeds are good for one year only, such as onions, parsnips, parsley, chives, shiso, scorzonera, Batavian endive, licorice, pennyroyal, St Johnswort, liatris, delphinium, larkspur, perennial phlox, and any seed that has been pelleted or hot-water treated. If in doubt, try germinating a sample of old seed in moist paper towels as shown above.
Tim Miner says
Great stuff! I have several seed packets that I bought last year at Whole Foods (Botanical Interests Seed Company) and I think I need to germ test the ones I plan to use this year.
Dave Creech says
I tested two year old spinach seeds and 3 year old carrot seeds. The spinach got me 50-60% germination which I wasn’t very happy with until I realized that the National Standard minimum germination rate for spinach is 60%. So it’s not far from where it should be I guess.
The carrots however were weak. I think I had one or two barely start to germinate after over a week in the paper towel. I think I’m going to end up ditching that seed.