Have an old packet of seeds and don't know if they will still grow? Put 10 on a damp paper towel; if fewer than 7 sprout, it may be time to replace them

That drawer of half-used seed packets from last spring doesn’t need to stay a mystery. University of Illinois Extension horticulture educator Brittnay Haag says a simple test with a damp paper towel can tell you within a week or two if old seeds are worth planting. Haag advises placing 10 seeds on a damp towel, rolling it up, sealing it in a bag, and placing it somewhere warm. If most of them germinate, the seeds are ready to go. If only a few do, then it’s probably time for a fresh pack. This is how the test works and why seeds slow down in the first place.

Why old seeds don’t sprout

A seed is considered viable as long as it can germinate under the right conditions. Every seed is a small sleeping plant, but it does not sleep forever. Heat and moisture slowly but surely break down the structures a seed needs to sprout, while cool, dry conditions allow it to hang on longer. This was directly tested in a 2019 study published in the Journal of Integrative Agriculture. Seeds of peas, lentils, and chickpeas were exposed to varying temperatures and moisture levels for the first seven years of a larger experiment. The results revealed that when both temperature and moisture remained low, the longevity of the seeds increased, but when the seeds were stored at higher temperatures and moisture, their germinability declined rapidly.


Seeds also vary in their longevity. Seeds of parsley and onion lose viability within one or two years, but seeds of melon, cucumber, and cabbage can remain viable for five years or more if stored under good conditions. Most seed packets are stamped with the year they were packed. As a rule of thumb, seeds are best used within three years of that date.

How to run the damp towel test at home

You do not need a lab for this. The test, sometimes called a rag doll test, is a classic used by extension offices and home gardeners alike. The University of Florida IFAS Extension has a guide for germination testing that walks through the basic version. Count out 10 seeds from the packet. Dampen a paper towel so it is moist, but not dripping wet. Spread the seeds on the towel and fold or roll it up. Put the rolled towel in a sealed plastic bag and mark it with the type of seed and the date. Keep it somewhere warm, preferably above 70 degrees Fahrenheit, like on top of the refrigerator or on a sunny windowsill. Check it every couple of days, and add a bit of water if the towel starts to dry out.

Reading the results: What the sprout count tells you

Once the seeds start sprouting, count how many of the 10 seeds have grown a root or shoot. This is the germination ratio. If all 10 seeds sprout, go ahead and plant your seeds at regular intervals as instructed by the packet. If seven to nine seeds sprout, Haag's guidance is to plant more seeds than the packet recommends to make up for the ones that won't germinate. If fewer than seven seeds sprout, according to Haag, it is advisable to buy new seeds. For larger seeds like beans, peas, and corn, there is a quicker check: put them in a bowl of water. As Haag puts it, seeds that sink are still viable, while seeds that float are essentially spent.

Make your remaining seeds last longer

If the test results are largely positive, it is worth preserving that success for next year. A cool, dry place is best for seeds, Haag says, ideally between 32 and 41 degrees Fahrenheit, which means a refrigerator is a good place. They can be stored in paper envelopes or in airtight glass containers, as moisture is one of the quickest ways to age a seed, a trend also found in the Journal of Integrative Agriculture study. Now that you know which seeds are still viable, she suggests sharing the extras with other gardeners, since a quick home test makes it easier to trade them confidently.

Testing old seeds requires very little effort compared to buying new ones each season, and it can turn a messy seed drawer into a head start on next year's garden. It usually takes a few damp paper towels, a warm windowsill, and a week or two of patience to find out what is still worth planting.