Tag Archives: stratification

Defining Common Horticultural Terms

Posted on by Scott Vogt

There are many horticultural terms that get tossed around in casual conversation. We hear these words or phrases in presentations, and read them in books and seed catalogs. Presenters often assume that everyone knows what they mean without much explanation. Here are a just a few words I use from time to time that I would like to define for you.

Xeriscape

Denver Water coined the term xeriscape in 1981 by combining landscape with the Greek prefix xero-, from (xēros), meaning ‘dry’. Xeriscaping = water-conserving landscapes. This landscaping concept focuses on several water conserving measures such as:

  • Planning and design that matches plants to the site
  • Water-efficient plant materials, especially native plants
  • Efficient irrigation systems including drip irrigation
  • Use of water-conserving mulch or densely planted gardens
  • Soil preparation only if necessary
  • Appropriate turf since it can be very water consuming

Something to remember: a xeric garden can still be a beautiful garden. It will just require less water over time so it’s a win, win situation.

Xeric garden at the Arboretum

Habitat

A habitat garden is a garden that mimics the natural landscape while also providing food, shelter and potentially water for wildlife, including pollinators. A habitat garden has layers of plants and a succession of blooms. It is a very intentional way of landscaping focused more on giving back rather than taking something from your landscape. Don’t get me wrong, a habitat garden can still be beautiful, but it will certainly give you much more enjoyment as you attract a host of pollinator, birds and other wildlife to your yard.

Stratification

One of the most interesting processes I learned when I first started working at the Arboretum was the process of stratification. It intrigued me that I could collect seed from the wild and get it to germinate in the greenhouse simply by simulating the chilling and warming that seeds would endure if left outdoors for the winter in their native climate. This chilling and warming that seeds are exposed to breaks down natural germination inhibitors until they are ready and able to germinate the next year.

This process is so important for plants and their survival because it keeps seeds from germinating the same year of development. They must go through a cold period such as winter before they are able to germinate. This does two important things: keeps seeds from germinating in the fall and allows the seeds to be worked into the soil over the winter with the natural freeze/thaw of the soil so they can germinate in spring.

If a seed would germinate in the fall, that tiny plant would not have enough time to develop a sustaining root system. The tiny seeding would not survive the winter. The natural process allows a seed to lay dormant all winter and germinated in the spring when conditions are more favorable for survival, it would have the entire growing season to develop a healthy root system.

This process of stratification is why we encourage people to scatter prairie wildflowers and grass seed in November and December. It allows time for this process to occur so the seeds will germinate the following year.

Hopefully, this is helpful. I will discuss some other terms in upcoming blogs.

2005 seed mix of wildflowers and grasses scattered on the Prairie Window Project at the Arboretum

Needy Seeds: How to Germinate Prairie Species

Posted on by Katie Schmidt

January and February can be dull months for a gardener. When the north wind whips and the drizzle freezes, spring seems a lifetime away. But here at the Arboretum these cold months are a busy time for seed treatment. Seeds we’ve collected and ordered are prepared according to their species-specific needs.

Photo from Dyck Arb

Seeds collected for the Prairie Window project being cleaned and sorted

Stratification

There are many specific types of stratification: warm-moist, cold-dry, cold-moist, water-soak, etc. Many prairie wildflower species require a cold-moist stratification period, a sort of “man-made winter”. Seeds are amazingly self governing, with built-in mechanisms to prevent germination until conditions are suitable. For species that have spent thousands of years adapting to the Great Plains, this means reading and reacting to seasons: long, cold, moist winter gives way to spring. Aha, time to sprout! It is the stratifyer’s job to convince the seed that winter has come and gone.

Cold stratification involves

  • first, mixing the seeds with media (sterile soil, sand, sphagnum moss, vermiculite)
  • wetting it slightly (too much moisture and the seeds will rot, too dry and they won’t germinate)
  • then storing in a refrigerator for a specified length of time

Each species is a little different – some need 60 days of cold, some need 120, and some just 10. Be sure to look up the requirements of each species if you are stratifying your favorites at home.

Common milkweed (Asclepias syriaca) seeds waiting to catch a breeze. 30 days of cold, moist stratification is all you need to germinate them for yourself.
Photo from: https://commons.wikimedia.org/wiki/File%3AMilkweed-in-seed.jpg

Scarification

Scarification is any process that weakens the seed coat, purposely making it more permeable to gases and water that trigger germination. In the wild, these seeds would only sprout after many years of freezing and thawing, or perhaps after being passed through the digestive tract of a seed eating animal. If you want to germinate tough-coated seeds for your own garden (and you don’t have the digestive tract of a bird) then you will need to simulate nature’s scarification processes. This is done by nicking seeds with a knife or rubbing with sand paper. Seeds naturally activated by wildfire may need to be treated with nearly-boiling water. Some seeds perform best after an acid bath! Every seed is unique.

Line drawing of prairie seeds by Lorna Harder. This is the featured graphic on our “Prairie Restoration” informational sign on the Arboretum grounds.

Fall Sowing Alternative

Fall sowing is often less work intensive than manual seed treatment. Let mother nature do the work of breaking the seed coat by sowing your seeds in late fall. The cycles of freezing and thawing mixed with intermittent winter moisture will produce much the same effect as the previously mentioned methods. But be patient – some seeds may take several years to germinate this way.

If you are looking for high quality native seed, Prairie Moon Nursery is a good source.

To find species-specific information on seed treatment, check out Growing Native Wildflowers by Dwight Platt and Lorna Harder, available in our gift shop.