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seed stratification techniques

Stratification and Scarification of Seeds

Give your seeds a head start

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Not all plant seeds are ready to sprout as soon as you put them in the soil. Some hard-shelled seeds need a bit more coaxing and some need a temperature change to trigger the end of dormancy. Scarification (cracking the hard outer shell) and stratification (fooling seeds into thinking they’ve been through winter) are two simple techniques that will save you a lot of frustration when starting seeds.

Stratification and Scarification in Nature

Stratification and scarification occur naturally when seeds stay outdoors through the cold winter.

Some seeds, like morning glories and lotus, have outer shells that are extremely hard and don’t allow water through. This is one way a seed stays dormant in the fall and winter until growing conditions improve.

Animals can also scarify seed by eating the hard seeds and digesting them. This is how strawberries can make their way around your yard.

Another way hard seeds can be cracked open is by leaving them outdoors throughout a cold winter. The constant freezing and thawing will be enough to get them to eventually crack. This process is generally referred to as stratification or cold stratification. Some seeds are not hardy enough for cold winter temperatures, but many perennial plants are started this way.

How to Stratify Seeds

Stratification is a means of simulating the chilling and warming that seeds would endure if left outdoors for the winter in their native climate.  

Some seeds will stay dormant until triggered by a certain amount of time in cold temperature or warm, damp conditions. This will occur naturally if the seeds are left outdoors or in a cold frame throughout the winter. Gardeners can break the dormancy of these seeds by mimicking the required conditions indoors.

To stratify seeds, start by placing them in some moistened peat, sand, or paper towels in a closed container or sealed plastic bag.   For cold stratification, place the container in the refrigerator. For warm stratification, store it somewhere where the temperature remains between 68 and 85 degrees Fahrenheit.

The length of time needed to stratify depends on the type of seed. Check every once in a while to make sure there is still some moisture in the container.

Selecting Seeds to Stratify

Seeds that benefit from being stratified tend to be perennials. It is a means for them to survive the winter and germinate when conditions are more favorable. This includes a lot of trees and shrubs along with perennial flowers such as apples, bugbane (Cimicifuga), butterfly weed (Asclepias), cranesbill geranium, day lilies (Hemerocallis), Delphinium, False Indigo (Baptisia), False sunflower (Heliopsis), fuchsia, Lady’s Mantle (Alchemilla mollis), Monkshood (Aconitum), perennial sunflower (Helianthus), poppies, and turtlehead (Chelone).

Some seeds, like Baptisia, may need both stratification and scarification. They need to have their outer shell opened before water can penetrate.

How to Scarify Seeds

Gardeners can scarify seed by gently rubbing the seed with something coarse, like sandpaper or a file, or by making nicks in the shell with a knife. You have to be careful when doing this.   You only want to crack the shell, not damage the seed inside or your fingers. Work gently. Some seed coatings are so hard to crack, many gardeners can’t scarify them without crumbling the whole seed.

Selecting Seeds to Scarify

Large, thick seeds such as morning glory, moonflower, nasturtiums, and purple hyacinth bean are the most likely candidates for scarifying. Although edible beans are large seeds, they will not need scarification.

Learn about stratification and scarification, two simple techniques that trick plants into germinating.

Wet Vs. Dry Stratification: Stratifying Seeds In Wet And Cold Conditions

One of the most frustrating things in the garden is a lack of germination. Failure to germinate can occur in seed for many reasons. However, when planting any seeds for the first time, it’s important to familiarize yourself with the specific needs of that plant. While some will germinate quite readily, others may need the use of seed stratifying methods to achieve optimal germination rates.

What are Seed Stratifying Methods?

Simply, seed stratification refers to the process needed by seeds to begin to germinate. These processes allow for moisture to move through the seed coat and initiate growth. The method gardeners can use to stratify seeds depends on the type of seed and the conditions under which the seed will begin to grow.

Wet vs. Dry Stratification

When it comes to stratifying seeds, there are generally two ways this can be accomplished: wet cold vs. dry cold.

Cold Stratification

Cold stratification is important for success in growing many annual and perennial plants from seed. This is due to the specific seed’s need to experience various weather conditions before it is ready to begin growing. This delayed germination helps the plant species ensure its survival, despite any unforeseen climatic events.

Stratifying seeds in wet and cold conditions is one of the most common treatments for hard-to-germinate plants. To cold-wet stratify seeds, you’ll need paper towels and a resealable plastic bag.

  • Wet the paper towel, and then spread the seed across it.
  • Next, fold the paper towel in half and close the bag. Label the bag and then place it in the refrigerator where it will not be disturbed.
  • Depending on the type of seed, leave it there for several days to a few months. Different plants will require different durations of cold treatment, so research your plant’s needs first.

After a suitable time has passed, the seeds can be removed from the bag and planted into the garden or into seed starting trays.

Dry Stratification

While wet-cold is most common, many plants also respond well to the dry-cold stratification method.

Like the wet stratification method, this technique requires that growers place their seed into a resealable plastic bag and place it into the refrigerator. However, dry stratification does not require any moisture. Leave the seed packets in cold treatment for the suggested period of time. Remove the seeds and plant them according to label instructions.

Although seed stratifying methods may seem time consuming, they are vital in improving the overall germination rate of many garden seeds. If you want to grow hard-to-germinate seeds without the use of refrigeration, consider the alternative of letting nature do the work. This can be achieved through proper storage of seed outdoors or through the implementation of the winter sowing method.

One of the most frustrating things in the garden is a lack of germination. While some will germinate quite readily, others may need the use of seed stratifying methods to achieve optimal germination rates. This article will help explain the wet vs. dry stratification methods.