Many landscape plants can be grown from seed, but with so many different plants it is much quicker and easier to propagate them from cuttings than it is to grow them from seed. Seedlings are so tiny and delicate when they first germinate that they require much more care than a cutting.
Seed propagation can be tricky. Many plants will not come true from a seed. In other words, the seedling produced from seeds that were collected from a red Rhododendron are not likely to flower red. More than likely the flowers will be a pale lavender. Seeds collected from a pink Dogwood will most likely flower white.
However, there are certain plants that must be grown from seed. Successful propagation of Taxus varieties is usually the result of propagating from cuttings, but Taxus Capitata, one of the most attractive varieties of Taxus will not come true from a cutting, but it will come true from seed.
Taxus Capitata is the most popular variety of the pyramidal shaped Taxus. Cuttings from this plant can be rooted and will grow just fine, but the plant will not have the natural pyramidal shape of the parent plant. The plants of this variety grown from cuttings, tend to grow more upright and require much more pruning to obtain the desired pyramidal effect.
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Other plants that are routinely grown from seed are plants that are extremely difficult to grow from cuttings. Many ornamental trees either can not be grown from cuttings, or if they are grown from cuttings the plants have weak root systems.
These ornamental trees will not come true from seed, but the plants that are produced from seed have good strong root systems that can be used as rootstock for the desired variety. This type of propagation is known as grafting. In this situation the desired variety is grafted on to the healthy, hardy root stock of the seedling. Grafting is discussed in detail in my book, Easy Plant Propagation, and is also demonstrated in my video How to Grow Your Own Landscape Plants from Scratch.
Growing landscape plants from seed is a little more difficult than growing vegetables. The seeds produced by most landscape plants will not germinate until they have under gone certain environmental conditions. Most seeds from landscape plants have a very hard, outer protective shell. Under natural conditions most of these seeds do not receive the proper treatment in order for the seeds to germinate. They just lay on the ground and either dry out or rot.
In different climates, different varieties of plants will grow naturally from seed. In eastern Pennsylvania for instance, Rhododendrons and Mountain Laurel grow wild on the mountain sides. Here in northern Ohio Dogwoods grow wild. Of course only a fraction of the seeds produced in the woods actually make it to the point of germination and survival.
Many seeds go through a period of internal dormancy right after the fruit falls from the tree. In some cases, there is actually a chemical barrier that prevents the seeds from germinating while they are still inside the fruit.
The hard protective coating on some seeds was designed by nature to protect the seed, but in many cases this protective coating actually inhibits the germination of the seed because water and air can not penetrate the hard coating.
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Many of these seeds actually require a double dormancy period before they will germinate. In other words, the seeds must lay on the ground completely dormant for one full growing season, and then germinate the following growing season. During the first season the only thing that is taking place is the outer coating is being softened by the elements. Once the outer coating is softened water and air can penetrate and germination can begin.
Timing is critical. Once the protective coating is softened, and the seeds begin to receive sufficient amounts of oxygen and water to begin germination, the plant will start to grow. However, if this takes place at the wrong time of the year, the young seedling will be destroyed by the intense summer sun, or the freezing temperatures of winter. That’s why, of the millions of seeds produced by landscape plants, so few actually germinate and survive to become adult plants.
As a gardener you can control when your seeds will germinate by initiating the pre-treatment and stratification at just the right time. You can actually fool some seeds into germinating much quicker by creating the necessary environmental conditions to soften the outer coating and initiate germination sooner. Let’s walk through growing Dogwood trees from seed.
Dogwood seeds ripen in the fall. When the seeds are ripe they will fall to the ground. You can leave them on the ground until they begin to show signs of shriveling, but be warned, the critters in your yard love them and are likely to beat you to them. Collect the seeds and place them in a container of water. Allow them to soak a few days to soften the fruit around the actual seed. After soaking for a few days, you should be able to squeeze them with your fingers forcing the seed from the pulp.
The good seeds will sink to the bottom of the container of water, any seeds that float are probably not viable. To separate the good seeds from the bad seeds and the pulp, turn your garden hose on very low and stick the end of the hose in the container and fill the container until it very slowly over flows. As the container over flows, the pulp and bad seeds will float out of the container. After a few minutes the only thing left in the bottom of the container will be the good seeds.
Once you have completely separated the seeds from the pulp, mix the seeds with some moist peat moss and place the mixture of peat moss and seeds in a plastic bag. The mixture should be moist, but not too wet. Store the bag at room temperature for a period of 100 days, and then move the bag to your refrigerator for a period of another 100 days.
This process softens the outer coating and allows germination to begin. The first 100 days of this process is a pre-treatment, and the second 100 days is known as stratifying the seeds. After the period of 200 days the seeds can be planted outside in a raised bed, or a flat of 80% peat moss and 20% coarse sand.
Make sure the sand you use is coarse. The purpose of the sand is to provide drainage. Sand with fine grains will not provide drainage.
Cover the seeds with a light layer of the growing medium that you are using. The rule of thumb for the correct depth of planting is twice the length of the seed, which is not very deep. If the seeds are 1/8 of an inch in length, they should be planted 1/4 inch deep or less.
Water the seed bed thoroughly after planting, and keep it watered throughout the growing season. It is better to water thoroughly and then let the bed dry out, almost completely, before watering again. This allows the sun to warm the soil in between watering. If you water lightly, but more often, you will keep the soil too cool. The seeds need the warmth of the sun as much as they need the water.
You can also speed the germination process by using a knife to make a very small cut or nick in the outer coating of the seed. Make sure you don’t damage the interior of the seed. This process allows water and air to enter the seed thus stimulating germination. With the dogwood seeds mentioned above, you could eliminate the first 100 day period of warm storage, by very carefully nicking the seeds, before placing them in the 100 day period of cold storage for stratification.
Cleaned seeds can be stored dry until they have undergone some form or pre-treatment. Just count backwards on your calendar from the day you would like to plant outside. If the seeds you are doing need 100 days of stratification, count backwards 100 days from the day you would like to plant. If they need 100 days of warm storage and another 100 days of cold storage, count backwards 200 days.
Another pre-treating technique often used, is treating the seeds with almost boiling water before storing them at a cool temperature. For instance, this technique is often used for Japanese Maple seeds.
Just place the seeds in a Styrofoam cup and fill the cup with extremely hot water, but not quite hot enough to boil. Allow the seeds to soak in this water as it cools overnight. Remove the seeds from the cup and place them in a plastic bag with the peat moss mixture as mentioned earlier, and store them in the refrigerator for a period of 90-120 days.
This process helps to soften the outer coating and eliminates storing them at room temperature for 100 days.
Seeds with a hard outer coating need one of the pre-treatments mentioned here, prior to the stratification period. One of the pre-treatments must be done prior to the stratification period. Just look in the How to Grow What section of this site to find the details for the plant you would like to grow.
When planting seeds outside in the spring you should wait until after the danger of frost has passed before sowing the seeds. Here in northern Ohio it is best to wait until after May 15th to be safe. You should count backwards on your calendar from the planting date, so you know when to start stratifying the seeds. With different kinds of seeds, and seeds from different plants, the length of time it takes to stratify the seeds can vary considerably. Sometimes only trial and error will provide you with the correct stratification period for seeds from a specific plant.
Check your seeds at least once a week when you are stratifying them. Make sure they are not too wet, and if they need water give them a little drink. They should be moist, but not wet. If they are too wet, squeeze some of the water out. The bag should be closed but not sealed completely air tight. If you notice that 10% or more of the seeds have started to sprout, plant them right away. If it is not practical to plant them outside, sow them in flats indoors, and make sure they receive some light. If you see mold growing in the bag, apply a powder fungicide.
Rhododendron and Azalea seeds ripen in the early fall. The best time to collect them is when the capsules darken, before they begin to open. If you wait too long, they will be blown away by the wind. These seeds can be kept in a dry place at room temperature until spring planting, or you can plant them right away if you can keep them at about 70 degrees F.. Just sow them on top of a flat filled with a mixture of peat moss and coarse sand, and provide them with some light. Use a mixture of 20% sand and 80% peat moss.
When growing seeds outdoors it is helpful to build a wooden frame and fill it with a mixture of peat moss and sand. Use a mixture of 20% sand and 80% peat moss. This will make it easier for you to control the moisture, and will also help to reduce weed growth. Topsoil is much more nutritional than peat moss, but unless the topsoil has been sterilized, it is likely to contain millions of weed seeds.
Some growers cover their seed beds with clear plastic as soon as they sow the seeds in the spring. This helps to warm the soil, and to retain the moisture. As soon as the seedlings begin to grow, the plastic is removed and some type of shading is provided. Snow fence suspended over the seed bed provides about 50% shade which is adequate.
Pines, spruce and firs are grown from seed. The pine cones are collected in the fall just before they open. Place them in a paper bag so when they open the seeds don’t get blown away. Store them in a cool dry place and plant them in a flat or a seed bed in the spring.
Most varieties of Hemlock require a stratification period of 30 days, in moist peat, in the refrigerator. The rule of thumb for determining how much peat moss to mix with the seeds, is four times the volume of the seeds.
Some seeds germinate immediately after falling from the tree. Most varieties of Oak trees fall into this category. For specific information on each variety see the "How to Do What" link.