Seed Stratification Explained- Part 2

In part 1 of this blog post, I explained what stratification is and why you need to do it. In part 2, I'll walk through three techniques to stratify seeds.

The first technique is simply allowing the seeds to stratify naturally outdoors by planting in the fall. In this blog post I provide instructions for fall planting. This technique is the least time consuming, however seed survival rates can vary depending on the number of critters around that may be tempted to eat your seeds. We have a huge population of mice and voles on our farm, so when we fall seed, we purposely overseed in anticipation that a lot of the seed will get eaten.

You can have a lot more control over seed survival and get a more accurate idea of germination rates by cold stratifying seed yourself. Here are two ways we recommend stratifying your seed.

The first technique is the Long Stratification Technique. This is the most common and most effective means of cold stratifying seeds. Here are some step-by-step instructions:

1) Ensure your seed requires cold and moist stratification. Some natives do not, so make sure to read your germination instructions carefully.

2) Grab a reusable container and either a dry erase marker or a label, and record the name of the plant, the date you started stratification and the date stratification should be complete. For many of the species we sell, we recommend 6-8 weeks, however 4 weeks is generally enough to do the trick. Alternatively, you can use a plastic bag and permanent marker.

3) Combine your seed and a sterile medium (I like vermiculite and perlite) in your reusable container or bag and add enough water to wet the mixture, but not enough that there's water swishing around in your bag. You want the medium to be sterile, that is new or sterilized (by leaving it out in the sun for example) because you will be leaving the seed in a moist environment long enough for mold to form otherwise, which can kill your seed. I don't recommend using soil, sand or paper towel for this reason.

4) Ring out any excess water from your seed and sterile medium mix, either by squeezing the mix with your hands, or by squeezing the bag. Pour off any excess water.

5) Put your container or bag in the fridge and check weekly to ensure it is still moist enough. Add additional water as required. If the seeds start to germinate, remove all of them from the fridge and plant. Do not put the seeds in the freezer, as a quick, flash freeze will damage their tissues and can kill many of them.

6) Either at the end of your stratification period, or when your seeds begin to germinate (whichever comes first), plant your seeds, along with the mix as well if you'd like. Don't worry if some or none of the seeds germinate by the end of the stratification period, many species don't at all. Plant your seeds indoors under a grow light or in a full sun window, or in a prepared seedbed outdoors.

7) Care for your seeds as prescribed on your seed packs and enjoy watching them grow.

The second technique is the Quick Stratification Technique. This 7 day stratification technique is a good option if you are getting a start on stratification later in the season, but germination rates can be a bit lower than the longer stratification method.

1) Ensure your seed requires cold and moist stratification. Some natives do not, so make sure to read your germination instructions carefully.

2) Grab a reusable container and either a dry erase marker or a label, and record the name of the plant, the date you started stratification and then I add in 4 check boxes under the word 'fridge' and another three check boxes under the word 'freezer'. Alternatively, you can use a plastic bag and permanent marker.

3) Combine your seed and a sterile medium (I like vermiculite and perlite) in your reusable container or bag and add enough water to wet the mixture, but not enough that there's water swishing around in your bag. You want the medium to be sterile, that is new or sterilized (by leaving it out in the sun for example) because you will be leaving the seed in a moist environment long enough for mold to form otherwise, which can kill your seed. I don't recommend using soil, sand or paper towel for this reason.

4) Ring out any excess water from your seed + sterile medium mix, either by squeezing the mix with your hands, or by squeezing the bag. Dump off any excess water.

5) Put your container or bag in the fridge for the first day.

6) On day two, put your container or bag in the freezer. I know I mention above not to put your seeds directly in the freezer, but the difference here is that you've already cooled them in the fridge, so in this case the additional cooling will be gradual and not damage the plant cells.

7) Alternate between fridge and freezer for 7 days, checking your seeds daily. Add additional water as required. If the seeds start to germinate, remove all of them from the fridge and plant.

6) Either at the end of your stratification period, or when your seeds begin to germinate (whichever comes first), plant your seeds, along with the mix as well if you'd like. Don't worry if some or none of the seeds germinate by the end of the stratification period, many species don't at all. Plant your seeds indoors under a grow light or in a full sun window, or in a prepared seedbed outdoors. In terms of when to plant in the spring, many wildflower seedlings are frost tolerant, but it's overall best to wait until the risk of frost is past since this will ensure the healthiest plants. In most Canadian regions this is the beginning of June at the earliest.

7) Care for your seeds as prescribed on your seed packs and enjoy watching them grow.

A last note about when to plant. While spring seeding is convenient, since cooler, moist spring temperatures are great for seedlings, you can really plant your wildflower seeds at any point in the summer, and as I mention fall is a great time too. Because natives are long-lived, there is no rush to get them in the garden early like you would say for a tomato variety that needs a full 90 days to fruit. The goal of a native plant's growth in the first year is to establish strong roots, so the earlier you plant the larger your plant and it's root system will be, but it will do fine planted later in the season as well. Do note, that if you plant your seeds late in the summer, when the heat is more intense, you will need to care for your seedlings much more carefully to ensure that they are getting adequate water and not drying out.