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Have you ever been frustrated in trying to grow wildflowers from seed? It turns out many native perennials - plants that come back year after year - are actually quite tricky to grow from seed. They often have specific needs that must be met in order for them to sprout or germinate.
Take Common Milkweed (Asclepias syriaca), for example, which many people are now trying to grow to support the Monarch butterfly. Monarch caterpillars ONLY eat milkweed - they physically can't digest other plants. Plus milkweeds support many other insects as well! The US Forest Service estimates over 450 insects depend on and consume various parts of the milkweed plant! Amazing! They are like a supermarket for bugs and biodiversity! Many milkweed seeds, including common milkweed, need a cold period - a mock winter - to sprout. For common milkweed, that mock winter or "cold stratification period" is 30 days. That means the milkweed seed needs to be moist and have at least 30 days when the temperature is between 30 and 45 degrees F. Temperatures that are colder or warmer than that window don't count towards the 30 days of "winter". What picky germinators!
To find out if your seeds need a "cold stratification period" or any other needs, I like to use a seed supplier website like Prairie Moon Nursery and search directly for the my plant that I'm trying to sprout... in this case here's what the profile of common milkweed looks like on the Prairie Moon website: https://www.prairiemoon.com/asclepias-syriaca-common-milkweed. Common Milkweed is listed with the germination code of "C(30)" which means it needs 30 days of cold.
There are several ways to get your 30 days of chilliness that Common Milkweed needs in order to sprout:
1) Scatter or plant the seeds in the fall to let them go through a full natural winter.
2) Plant the seeds in trays and stick them out in the rain and snow of winter (make sure they stay moist!) and then you can either let them sprout outdoors slowly as spring comes or bring them inside to a sunroom or sunny window or greenhouse to speed up the process.
3) Use the refrigerator technique: stick the seeds in a coffee filter and stick them in the back of the refrigerator for at least 30 days... who knew that the refrigerator would be the PERFECT cold stratification chamber!
A backyard in winter is great for germinating wildflower seeds that need a cold stratification period.
I must say that the seeds-in-coffee-filter-in-refrigerator technique is fast becoming my favorite way to cold stratify wildflowers. It works unbelievably well as the refrigerator is the perfect temperature (not too cold, not too warm) and the sprouting or germination rate from this method is excellent! Some need only a short bit of cold like the Purple Coneflower (Echinacea purpurea) at around 5 days. Other seeds require more like Cardinal Flower (Lobelia cardinalis) at 60 days.
What are some other weird requirements of certain wildflowers?
Scarification: Some seeds to be scuffed up, scratched or scraped on the outside in order to germinate. One example of this is Wild or Sundial Lupine (Lupinus perenis), our native lupine, which is also the primary host plant for the federally endangered Karner Blue Butterfly (its caterpillars ONLY eat this lupine's leaves!). To scarify, I typically rub the seeds between two pieces of rough sand paper or on a rough rock. Then, as in the case of lupine, I put them in a coffee filter for a cold stratification period of 10 days before planting.
Light Requirement: Some seeds need just a little bit of sunlight in order to germinate. OR they are just so small, you need to be careful to put them on the surface of the soil (instead of buried) to allow them to germinate. Seeds like Cardinal Flower, Great Blue Lobelia and many Goldenrods have this need. My favorite way to give access to light but also protect them from getting blown or watered away on the soil surface is to sprinkle a layer of sand overtop of the seeds when planting.
Hot Water Treatment: Some plants have a very hard outer seed coat and benefit from a hot water treatment. New Jersey Tea (Ceanothus americanus) is one such plant - dried leaves used for tea during the Revolutionary War and also a host plant for the Spring Azure butterfly. Take boiling water and pour it over the seeds, then let them soak for 24 hours before cold stratifying. I've also used this method for nuts like the American hazelnut.
Multiple Seasons: Some seeds need multiple seasons of cold then warm to germinate! Pasture or Carolina Rose (Rosa carolina) is one such plant that not only needs to be scarfied but also needs one winter, then a long warm period (summer), then a 2nd winter in order to trigger germination!! Definitely a challenge for any gardener! But worth it as it is an amazing pollen source in the spring for endangered bumblebees which need pollen to grow baby bees!
Needs a Host Plant: This is probably one of the weirdest needs of certain wildflowers like Indian Paintbrush (Castilleja coccinea) or Wood Betony (Pedicularis canadensis) also known as hemiparasitic plants that require a host plant (usually a grass species) in order to germinate! Blue Grama (Bouteloua gracilis), Little Bluestem (Schizachyrium scoparium), and Pennsylvania Sedge (Carex pensylvanica) are all great host species for these flowers which attach to their host plants roots (like a parasite) in order to flourish. You do this in a number of way: you can seed the plant at the same time as seeding its host plant, add in the hemiparasitic species when transplanting the host, or make a cut into the root mass of existing grass where you seed in your hemiparasitic flowers! It's weird, but it works, and these species won't grow reliably without their host plants!
Now ... no wonder wildflowers are difficult to seed?! Yet when you know their secrets, they really aren't as bad as they seem to get established.
Lastly, a note on scientific names: I used to prefer common names over the scientific one. I mean who can really pronounce them anyways, right? Much less spell them?! But at last I have come around as I began to get to know the plants better. Some plants might look totally different from each other but be in the same family and knowing the scientific name gives you clues about a bit of their history, personality and character traits. It's a slow process to learn these names but I recommend writing out the scientific names when you can and slowly sounding them out once in awhile. After a while, they roll off the tongue, much like (in my mind, at least) the way wizards and witches of the Harry Potter books practiced Latin-sounding spells over and over to get them right with the flick of a wand. And knowing how to sprout these magnificent and often underrepresented plants in the landscape feels a lot like magic.
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