Today we are going to start a mini-series on how to propagate plants. Different plants are successfully propagated using different methods. There is no one size fits all solution to making more of your garden plants. So in the next several articles we will be discussing tips for propagation via seed, cuttings and grafting.
Because seeds are often the easiest and cheapest way to get new plants we are going to start our series with seed propagation. As you probably know, most flowering plants produce seeds. The purpose of the flower is reproduction. As a general rule, seeds need warm moist conditions to germinate.
Not all seeds germinate equally well or under the same conditions.
The seeds of annual plants typically germinate very easily. These are most of the seeds you can buy at stores in the spring. There entire existence relies upon seeds germinating, so that makes sense. Seeds of perennials and woody plants often are much more difficult to get to germinate. However, if you know the tricks of the trade you can successfully germinate these seeds also.
If you are interested in germinating some of these more difficult seeds you may need to utilize various techniques to mimic the natural conditions they would typically germinate under. Many plants have some sort of germination inhibitor that must be overcome to allow the seeds to germinate. The reason they have this is to ensure their survival.
Luckily, we humans have determined the optimum germination conditions for almost any seeds you’d want to germinate. We also have access to the internet allowing us to quickly determine what sort of environment different seeds might need to successfully germinate. If you would like to germinate some more difficult seeds, or have had trouble getting seeds to germinate, read on to learn more about various techniques used to encourage seed germination.
Stratification

Some plants require what is called cold stratification, while others require warm stratification.
Warm stratification mimics the heat of summer, and it requires a period of keeping the seeds moist at elevated temperatures. It is less commonly needed than cold stratification, but when needed can be accomplished by keeping the planted seeds on a heat mat.
Cold stratification mimics the cold of winter, and the warming of spring. It is an important survival technique that prevents seeds from germinating in the late summer or fall and then dying over the winter before they have opportunity to get established enough to survive the winter. Cold stratification is planting the seed in moist conditions and then chilling them for the required amount of time. Once the seeds have been chilled, they are moved to warm conditions to germinate.
You can accomplish cold stratification by planting your seeds in a pot and then placing the pot in your refrigerator. Another way to accomplish stratification is through fall or winter sowing seeds. For difficult to germinate seeds (like passion flower seeds), winter sowing may be one of the best ways to get them to germinate. The reason for this is that because of the freezing and thawing winter sowing combines both stratification and scarification which we will discuss next.
Some examples of seeds that benefit from cold stratification include columbine, balloon flower, black eyed susan, lavender, catmint and cone flowers.
Scarification

Scarification is the act of damaging the seed coat which will allow the seed to absorb moisture and germinate. There are various ways to do so, and which method works best depends on the species you are working with.
There are a couple different scarification methods commonly used. The first of which is through mechanical damage. This might be accomplished by clipping off a portion of the seed coat, or rubbing the seeds with sandpaper. In nature this sort of scarification would occur via the soil rubbing the seeds over time, and through the freeze thaw cycles in winter.
Another method commonly used is treating the seeds with an acid like sulfuric acid, or boiling water. The acid/boiling water as you might imagine damages the seed coat allowing the seed to germinate. As you might imagine this is often a preferred method to mechanical damage as it is much more easily and consistently accomplished in an artificial environment.
Examples of seeds that benefit from scarification include lupine, milkweed, morning glory, and many woody plants/trees.
Some seeds require stratification, some require scarification. Some require scarification followed by stratification. Other seeds have different environmental requirements that must be met.
Light Condition Requirements for Seed Propagation

If you aren’t interested in growing perennials or woody plants from seed, you might never have to worry about stratification or scarification as annual seeds do not typically require either. However, there are many annual seeds commonly grown that have specific light requirements. If you’ve wondered why your seed packets or hand gathered seeds didn’t germinate well, its possible that their light requirements were not met during germination.
Some seeds require light to germinate and some require total darkness. Applying the correct light conditions helps to ensure that the seeds are germinating under conditions suitable for them to have a chance to survive. For example, many plants with very tiny seeds require light to germinate. They do not have the strength or nutrition stores to grow a long way to reach the soil surface. Requiring light for germination ensures that the seeds are near the surface of the soil before they germinate ensuring a chance at survival.
Conversely, requiring darkness ensures that the seeds are buried where they will have consistent moisture to allow them to germinate. Most seeds would prefer a dark moist environment to grow, however if your seed packet says to surface sow or to only lightly cover the seeds, you can bet they require light to germinate.
Examples of seeds that have light requirements include poppies, purslane, and lettuce.
Temperature requirements

In addition to light conditions many seeds, particularly annuals have specific temperature requirements. These can be minimum or maximum temperatures at which the seeds will or will not germinate. Most seeds have an optimum germination temperature, often around 70-75 degrees. Some seeds have very broad temperature ranges in which they germinate. For some the range is very narrow. Some seeds need cool soil. Some need soil temperatures of 80 degrees or more.
Similar to how stratification and scarification prevent germination at the wrong time of year, so does required germination temperatures.
Obviously, all those annuals that you’ve had in your garden all summer set seed in the fall before they died. However, the plants do not want those seeds to germinate until spring. Requiring warmer temperatures prevents the seeds from germinating in the fall when they would quickly die in the cold temperatures. Of course, some plants are cool season plants and are very cold hardy. In those cases, it is important for germination to be inhibited under lethal hot conditions. These plants will drop seeds in the spring before they die. Those seeds won’t start germinating until the fall when the soil temperatures cool.
Some examples of seeds that have specific temperature requirements include spinach and pansies (need cool temperatures), and begonias and impatiens (require warm temperatures).
We hope that this helps you to up your seed germinating game. Now that you know how complex germinating seeds can be, if you are having trouble germinating seeds don’t hesitate to check online for what conditions must be met. In the next article of this series we are going to take a look at how to grow plants from cuttings.
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