By Susan Harkins
Growing new native wildflowers from seed is inexpensive and satisfying if you really enjoy the hands-on approach. In Kentucky, most native wildflowers require some form of preparation, such as stratification or scarification. In this article, you’ll learn how to stratify your seeds, because it is the most common method required by Kentucky natives.
Stratification, defined simply, is the act of creating layers. For our purposes, stratification is the process of breaking down a seed’s outer protection so it can germinate. Nature does a great job of this. When seeds drop to the ground, they overwinter in the cold, moist soil. The constant change in temperature and moisture works to grind or dissolve the outer covering. By spring, many of these seeds are ready for the warm spring weather and germination. Many Kentucky natives will reseed year after year without any human intervention.
If you want more control, you can collect seeds and force the germination in flats, pots, and even milk jugs. But for most of the native seeds you collect, you can’t wait until spring to sow them — they won’t germinate until the next year, if at all.
How to prepare seeds manually using stratification
Sowing seeds outside is easy, but sometimes disappointing because Kentucky winters are often too mild to properly stratify your seeds. Some people force the issue by preparing their seeds in the refrigerator (don’t freeze them). Or, you can prepare the seed trays in November or December and leave them outside. Over the years (literally), I’ve learned the hard way that no single method produced better germination consistently. For that reason, I’m going to share the easiest methods: wet paper towels, sand, or vermiculite.
Using paper towels
Paper towels are cheap, but seeds often stick to the towel, which makes it difficult to remove the seeds for planting. Use two moist paper towels, layering the seeds in between, leaving lots of room between the seeds. Don’t fold the towels, doing so will clump your seeds, making it more difficult to separate them for planting. Instead of using two paper towels, you can use one and fold it over once. After preparing your seeds between the layered paper towels, slip the towels into a zip lock bag and seal it. Mark the bag with the date and species. Put the bag in the refrigerator and forget about it until it’s time to transfer to a planting medium.
If the stratification period is long, check occasionally to make sure the paper towels remain moist. Be sure to seal the zip lock bag or the contents will dry out quickly and the seeds will be useless.
When you’re ready to plant, you can lay the paper towel out on your planting medium and cover lightly. There’s not need to separate seeds from the paper towel unless the seeds are clumped together.
Using sand
Sand is my least favorite method. It tends to dry out quickly and requires constant checking. It’s also difficult to remove the seeds for planting. You can spread the sand mixture by handfuls over your planting medium, but the sand just doesn’t offer the best control. If you try this method, use fine sand, add your seeds, place in a zip lock bag and place in the refrigerator.
Using vermiculite
You can use vermiculite or even moist potting soil, but vermiculite retains moisture longer. This is my favorite method because it’s so easy to move the contents to your planting medium. I grab a handful and roll it back and forth in the palm of my hands so the seeds are positioned well. However, this method will consume more refrigerator space, but unless you’re dealing with dozens of species, you should be able to squeeze these bags in somewhere.
If you have an extra refrigerator, you can skip a step. Prepare seed trays without holes with your planting medium, add your seeds, and stack them in the fridge. Keep an eye on them so the soil remains moist. Be careful not to overwater because the water will stand in the bottom of the tray. You might find that a spray bottle works better than watering. When the stratification period is over, you can remove the trays to a warmer area for germination. You’re completely bypassing that middle step of moving the seeds from the plastic bag to a plant medium, which can be tedious.
Using nature
If you prefer to let nature do the work, you can prepare seed trays with your planting medium, spread your seeds, and set outside in a protected area, such as a patio or beside the house. Doing so provides protection from strong winter winds.
Be sure to mark your flats or draw a map so you know what’s germinating next spring. Use flats with holes so the water doesn’t stand in the flat, causing seeds to rot.
Marking your trays can be difficult. I recommend an art paint pen because it’s more durable than even a Sharpie in the winter elements. A map is the most dependable because small mammals and birds will often eat your seeds and while doing so, displace your markers.
Many growers have adopted the milk jug method. You cut the jug in half, leaving enough of a connection to create a flipping lid. Fill the bottom with your growing medium, close the lid, and secure it with waterproof tape. The jugs create little greenhouses. As warmer weather arrives, you can flip the lids back, add a bit of water as needed, and leave them open for the day. But be sure to secure the lids at night while the nights are still cold. Once the seedlings are ready to plant, you can move to seedling trays or small pots.
The one issue you have with any outdoor method is Kentucky’s unpredictable weather. The stratification period requires a temperature of 40 degrees or lower for the period. It can be difficult to get 90 days of those colder days in Kentucky.
In spring, you’ll be moving these jug seedlings earlier than usual because the seeds germinate earlier in the jugs. Once removed from the safety of the jugs, be prepared to protect your seedlings when the nights turn cold. For more information on this method read, How to turn a milk jug into a mini greenhouse by Emilie Grace Yochim.
Just try it
If this is all new to you, I recommend that you try more than one method, just for the experience. You might find that one method works better for you than another, although I have never found this to be the case. I use the easiest and least expensive method because some years I have a bumper crop and some years, I sigh and buy fill-ins from a nursery because the resulting crop is so pitiful. You might also find that some species germinate easier than others. It’s trial and error, but you will learn fast.
Most purchased seed packets will include the length of the stratification period. If not, you can usually find a resource on line with a quick search. My favorite resource is Growing and Propagating Wildflowers of the United States and Canada by William Cullina. You might have to look for a copy in book stores that sell used books, because it’s been out of print for a long time.
Propagating trees and shrubs from seeds can be done, but cuttings are quicker and easier. Look soon for an article on this method.