Welcome to the blog! Thank you for taking an interest in the nursery and spending some of your precious time with us. I sincerely appreciate it.
Before getting into my first topic I want to explain what the purpose of this blog is and what you can expect from it. Humble Roots Tree Farm, very true to name, was started with humble beginnings. I started this business with a lot of passion and excitement about trees, but with considerably fewer resources in terms of finances and experience. In my first year running the nursery I learned a tremendous amount about growing trees and operating a business, but there is still so very much to learn. I look forward to this learning process, but it’s easy to feel a certain amount of imposter syndrome as I position myself as some level of expert when in reality I’m just learning right along with everyone else. One of my goals for Humble Roots Tree Farm is for it to be an educational resource in addition to being a source of high quality plants. By sharing both my successes and failures I hope this blog will serve others to that end.
Now, to the meat of the post! As we enter fall, we are officially in the seed gathering season, which means it's a good time to talk about stratification. Some plant species make seeds that are dormant and require exposure to cold (and in some cases warm), damp conditions for a period of time before they will germinate. These conditions are naturally met in the wild when seeds fall to the ground and nestle into for duff on the forest floor. In northern climates the seeds experience very cold temperatures, but are insulated from hard freezes by the leaf litter and a layer of snow. The exact science of how stratification breaks dormancy is beyond me, but my understanding is that dormant buds on an established plant contain growth inhibiting hormones that prevent them from opening during the winter. Cold temperatures start an internal process that breaks down these growth inhibiting hormones until they are gone (which hopefully coincides with the end of winter) at which point the buds will begin to grow. A similar process happens in dormant seeds.
Stratification is simply a process of artificially recreating these cold (or warm), damp conditions found in nature so that seed dormancy is broken in a controlled and convenient environment. Each species has particular requirements for type (cold or warm) and length of stratification. Cornelian cherry (Cornus mas), for example, is doubly dormant, which means it requires two cold stratifications separated by a warm stratification. So it pays to do some research ahead of time and plan out a schedule so that you have each species finishing stratification when you intend to plant in the spring. Seeds need to be put into some sort of media that will remain moist (without molding). Relatively inert materials like sand, coco coir, fresh sawdust or wood shavings can work well. I typically use coco coir and black locust or larch shavings (since both those species naturally resist mold and decay). When seeds are packed into the media you need to decide on a location to store them that will be cold (above freezing but at or below 40 degree Fahrenheit, which generally means in a refrigerator or outside in climates where winter temperatures get that low. There are pros and cons to both methods and I'll share my experience with each.
Refrigerator Method
Stratifying in the fridge offers convenient, indoor access to your seeds, accurate temperature control and protection from predation by critters. The downside is the potential for mold. Many folks steer away from the fridge for this reason, however, I've not found it to be a big issue. This is where choosing an inert media is very important. I pack my seeds in ziplock bags using damp coco coir or coarse sawdust (you should only be able to squeeze a drop or two of water out of a handful of the media). I label each bag with the species, quantity of seed and the start/end date of stratification. I also add a few drops of tea tree essential oil to each bag to help stave off mold and mildew. I've not heard of anyone else doing this and I've never done any scientific experiments to see if it's actually working, but, anecdotally, it seems to be effective as I have little to no mold issues when stratifying in the fridge. Lastly, I make sure to keep the ziplock bags partially opened to allow air flow, which also helps prevent mold from getting started.
Outdoors Method
Stratifying outdoors is appealing because you can much more easily process large quantities of seed that would quickly use up an entire refrigerator (and if your fridge is also used for storing food this becomes problematic). The outdoor method also has the benefit of reducing the potential for mold. The downsides to the outdoor method are twofold. First, is predation by hungry critters, who can be shockingly persistent when it comes to accessing food sources. Secondly, is the potential for the seeds to freeze. Most seeds will not tolerate hard freezes (or, as is the case with chestnuts, any freezing at all). Remember that in nature seeds fall from the parent plant and nestle down into the leaf litter below and are often blanketed with snow for much of the winter, both of which offer significant insulation. A way to get around both the predation and the freezing issues is to bury the seeds under ground in some sort of container, where they are protected from hard freezes and from being easily accessed by critters. A tried and true method is to pack the seed/media mix into a five gallon bucket with a snap on lid with drainage holes drilled into the top lid and the bottom of the bucket. This allows water to drain into and out of the buckets and allows air flow through the bucket. I also cut circles of 1/4" hardware cloth to fit into the bottom of the bucket and on top of the seed/media mix so that there is another level of defense should any rodents chew through either end of the bucket. The bucket is then buried in the ground so that the top is level with the ground. For good measure you can place a heavy rock on the lid and then cover the whole thing with a thick layer of mulch. I have had great success with this method but it comes with a word of caution: only attempt this method if your soil drains very freely. I used this method when I lived in the Willamette Valley in Oregon. I had great soil on my property that drained well and the buried bucket method worked like a charm. In my current site in Upstate New York I have very heavy clay soil that, once saturated, takes weeks to drain. In my first season here I used the buried bucket method like I had previously, but failed to take into account how poorly the soil drained. The holes that I dug acted like sumps and filled up with water and didn’t drain completely until summer. I lost a lot of good seed by making that mistake. As with most things, a little foresight can go a long way!
I still want to be able to stratify outside so my solution has been to create a “bin” out of used pallets that houses my stratification buckets. Here's picture of it partially completed and in its final state:
Inside the bin I put down a thick layer of wood chips on the ground to insulate and allow water to have a place to go when it drains out of the buckets, I then put all my buckets in the bin and surrounded them completely with more wood chips. The bin should be big enough that there is at least a foot and a half of chips between the walls and the buckets in order to allow for a good bit of insulation. There should also be about a foot and a half of chips on top of the buckets. I located the bin in a spot somewhat sheltered from the wind, but on the faces where wind could still hit it directly and push the cold deep into the bin I lined the walls with cardboard before filling with woodchips. After a few good rains I put a layer of cardboard or a tarp over the top to keep too much rain and snow melt from getting into the buckets and creating a soggy environment for the seeds. Last winter was my first time using this bin method and it worked very well. I had very high germination and very few instances of mold or rot. I'll be doing it again this year!
If you’d rather skip the effort of stratification, I plan to offer fully stratified and ready to plant seed of several species in the spring. I’ll update the inventory this fall and you can check it out here. Or if you’d like to go straight to the seedling part of the process, check out our offering of fruit and nut trees here.
Thanks for reading and let me know in the comments section if you have any questions or have some cool tips and tricks for successful stratification!
Happy growing!
Keith