The process of growing a tree from seed takes time and patience. It also requires knowledge about the seed's germination requirements and the understanding of how each phase takes place. This guide will attempt to explain the process and clarify the techniques used to successfully germinate tree and perennial seeds. (If you need seeds, we sell them here.)
First: A Shortcut To Growing A Tree From Seed
Well, it's not a shortcut in time, but it is a shortcut in technique. The easiest way to grow a tree from seed is to copy a squirrel: plant the seed outdoors in the fall and leave it. The seed will go through winter's natural freeze and thaw cycles and sprout the following spring... or the spring after that. It works perfectly well and is used by many experienced growers.
But maybe you bought your seed mid-winter, or you need your seed needs to germinate on a specific schedule, or you don't like copying squirrels? Read on.
What Is Seed Pretreatment?
Pretreatment refers to the various processes applied to a seed before planting (and sometimes after) in order to wake it from dormancy. These techniques either make germination possible or enhance the germination rate.
Common seed pretreatment methods include:
Stratification - Cold stratification exposes the seed to a period of cold temperatures to simulate winter conditions. Sometimes a seed needs both cold and warm stratification.
Scarification - Damaging, scratching or breaking the hard seed coat to facilitate water absorption.
How do you know what pretreatment your seeds require? There are many propagation manuals, seed catalogs and web databases which can give this information. Here is an example of pretreatment requirements for five commonly grown tree seeds.
Tree Species | Stratification Needs | Scarification Needs |
Hybrid American Hazelnut | 60-90 Days, Cold, Moist | None |
Chinese Chestnut | 60-90 Days, Cold, Moist | None |
American Persimmon | 60-120 Days, Cold, Moist | None |
White Oak | 60-120 Days, Cold, Moist | None |
Peach | 60-120 Days, Cold, Moist | Yes, Grind Edges |
Stratification: Mimicking Nature
Stratification is a seed pretreatment method that simulates natural conditions to break dormancy and promote germination. It involves exposing seeds to specific temperature and moisture conditions for a period of time.
Types of Stratification:
Cold stratification: Seeds are subjected to cold temperatures (typically between 32°F and 41°F). This is commonly used for seeds of plants native to temperate climates.
Warm stratification: Seeds are exposed to warm temperatures (typically between 65°F and 80°F). This is often used for seeds from tropical or subtropical regions.
Moist stratification: Seeds are kept moist during the stratification process. This is the most common type of stratification and is almost always needed in order to grow a tree from a seed.
Dry stratification: Seeds are kept dry during the stratification process. This is less common but can be effective for certain species.
How To Stratify Seeds:
Choose a container: Use a small container or zip-top bag.
Prepare the seeds: Clean the seeds and remove any debris.
Add a moist medium: Place the seeds in a moist (not wet) medium, such as vermiculite, peat moss, sand, or a mixture.
Seal the container: Close the container or bag to maintain humidity.
Store in the appropriate temperature for the amount of time the seed requires: Place the container in a refrigerator for cold stratification or a warm location for warm stratification.
Monitor and adjust: Check the moisture level periodically and adjust if necessary. Check for mold or decay and replace the medium, if needed.
Remove and plant: After the specified stratification period, remove the seeds and plant them according to the appropriate planting instructions given for the seed.
The duration of stratification varies depending on the species and the specific requirements for breaking dormancy. Consult seed packets or online resources for species-specific information. You can also reference specialty nursery manuals which give germination information for most common tree seeds.
Scarification: Adding A Little "Persuasion"
Scarification is a technique used to break the hard outer coat of seeds, allowing water to penetrate and initiate germination. This is particularly necessary for seeds with thick, impervious seed coats, such as peach seed.
Methods of Scarification:
Mechanical scarification:
Nicking: Using a sharp knife or a file to make a small nick in the seed coat.
Rubbing: Rubbing the seeds against sandpaper or a rough surface to wear away the outer layer.
Gnawing: Coating the seed in peanut butter and letting Fido chew on it. Just kidding, don't do that.
Chemical scarification (better suited to lab environments):
Acid treatment: Soaking seeds in a weak acid solution (e.g., sulfuric acid) to soften the seed coat.
Concentrated sulfuric acid: Using concentrated sulfuric acid for seeds with extremely hard coats, but this method requires caution due to the corrosive nature of the acid.
Hot water scarification:
Soaking: Soaking seeds in hot water for a specific period to soften the seed coat. The exact temperature and duration vary depending on the species.
Now It's Time To Plant
Once seed pretreatement is complete you can plant the seeds. Reference materials will give detailed information about a seeds specific requirements. After you have soaked, scarified, stratified and fully treated the seeds, you can plant them.
Growing them indoors or in a greenhouse environment is fine. Plant the seeds into pots with drainage holes, using a well draining potting mixture.
You can also plant the treated seeds in their final growing location outdoors. Remember to protect them from rodents and other wildlife that enjoy snacking on tree seeds.
How To Store Tree Seeds
Storing your seeds properly will extend their life and keep them viable for long periods of time. Seeds stored properly can remain viable for many years, while those stored improperly may quickly lose their ability to germinate.
Factors Affecting Seed Storage:
Moisture: High humidity can promote mold growth and reduce seed viability. Seeds should be stored in a dry environment.
Temperature: Extreme temperatures can damage seeds. Cool, stable temperatures are ideal for long-term storage.
Light: Exposure to light can accelerate seed aging and reduce viability. Seeds should be stored in darkness.
To summarize the optimal seed storage environment: cool, dark and dry.
Seed Storage Methods:
Seed packets: Store seeds in their original sealed packets in a cool, dry place. Paper packets breathe and prevent problems from excess moisture if seeds were not fully dried before storage.
Glass jars: Store seeds in airtight glass jars along with a silica gel packets to absorb moisture.
Refrigeration: For long-term storage, seeds can be refrigerated in airtight containers.