Contributed from Garden and Greenhouse Magazine
Written by Michelle Moore
Starting Seeds in the Winter
It’s amazing to think that the largest living object on earth emerged from a seed measuring only 3 to 5 millimeters, about the same size as a tomato seed. The giant sequoia can grow to be over 350 feet tall with a trunk diameter measuring more than 25 feet. How did that tiny seed contain such an enormous and beautiful tree? How does a tiny seed barely visible in your hand grow ripe red tomatoes the size of a softball? Watching the process take place is truly magical. While there is still much unknown about the plant world, there are some ways to ensure you have success when planting your own seeds.
There are many great resources for someone wanting to start their own seeds, yet many people find the process either frustrating or intimidating. Admittedly, it can be both, but it does not have to be a challenge. While I’m not a botanist, or horticulturist I’ve found studying botany and plant science not only useful but interesting. The more I learn, the easier it is to make small adjustments to obtain better results. Armed with a basic understanding, growing plants from seed is still magical, but now it’s not mysterious. Two books I’ve found particularly useful are Practical Science for Gardeners by Mary Pratt, and Botany for Gardeners by Brian Capon. Marry Pratt’s book does an especially good job of breaking down the science and technical jargon into easy to understand language.
What is a Seed?
A seed is a tiny miracle designed to ensure the continuation of a species. Seeds contain all of the genetic material of the plant it will eventually produce or in other words an embryo and enough stored food to feed the plant until it develops the necessary parts to feed itself. The plant size is genetically predetermined with all of the instructions bundled in the seed. When exposed to favorable conditions, the seed will come to life. Some of the plant’s tissues programmed to grow with gravity form roots, while others from the stem and leaves. Seeds contain roughly 2 percent water compared to 95 percent water in a mature herbaceous plant[i]. These dehydrated packets are preserved and stored until they are ready to grow themselves. Nature developed many systems to ensure these seeds have the best chance of reproducing. Understanding some of these requirements will help you succeed when you grow your own plants.
Starting seeds indoors not only gives young plants a jump start, the success rate is much higher. Seeds planted indoors are not threatened by many of the object hazards outside. Seeds planted outside face cold temperatures, rain that may displace the seeds or bury them deeply. Birds, rodents or other creatures feed on the nutrient rich seeds or tender little seedlings. Wind may remove the top layer of soil blowing seeds away, or deposit leaves or other matter on top of seed beds blocking the light. Soil quality is another factor. It’s also easier to control the growing media when planted indoors.
What do Seeds Need to Germinate?
For the sake of simplicity, let’s assume the seeds you are using are ready to plant immediately. Some seeds require periods of cold, heat, intense rain or some other trigger in order to germinate. Most commercially available seeds are already processed and ready to plant. If you are harvesting your own seeds, you may need to learn more about the plant’s native environment for clues to germination triggers if you do not have success initially. Assuming your seeds are ready to plant, you will need to introduce moisture, heat and light to germinate most seeds. By controlling these factors, you can better control your results.
Moisture
The seed is covered by a protective coating called a seed coat. In order to trigger the germination process, seeds must have a consistent source of moisture. Soaking seeds for up to 12 hours prior to planting will disperse water through the tissues allowing the seed to expand to roughly two times the previous size. This expansion will crack the seed coat and will allow the roots to push out of the seed and anchor the seedling to the soil. Once roots are established, the roots grow millions of microscopic root hairs that deliver water and minerals to the rest of the plant. Inconsistent watering or the incorrect media could significantly stunt the roots ability to move the water to the rest of the plant.
Experts frequently recommend sifting though soil to remove large particles and rocks before planting. This is done in part to ensure small roots and root hairs do not find themselves in air pockets that do not contain moisture. These small root hairs must have constant access to water to survive. Since the root hairs increase the plant’s ability to transport water from the soil to the plant for photosynthesis they are critically important for healthy growth. Dead spaces in the soil or planting media inhibit root growth. Some planting media include soilless potting mix, specifically formulated seed starting mix, coir fiber or rockwool for hydroponics. Most growers have their favorite substrate, mine happens to be coir because it retains moisture while maintaining a lose consistency. This ensures roots don’t drown or suffer from lack of oxygen, but are unlikely to dry out. When watered from the bottom, coir easily wicks moisture distributing it evenly. Coir is neutral, so adjusting pH is not an issue, however, there is no nutritional value to coir. As soon as the first leaves emerge, plants must be fed or they will be undernourished for a critical time in their development.
Light
Some seeds require darkness to germinate, but most require bright light. The light signifies the end of winter, a location with enough sunshine for growth, or a long summer day. This light cue begins a hormone reaction in the seed that starts germination. When growing indoors, light is an important consideration. In a greenhouse, seeds receive light, but the day length may not be long enough to trigger germination for some seeds so supplemental light is necessary. In this case the goal is to create a longer day length. Using a grow light on a timer to supplement the shorter winter days is easy to do and can be quite inexpensive to operate. When seeds are started in other indoor locations, more light is needed to supplement the lack of natural light. As a general rule of thumb, more light is better than less, however, plants, just like people, need to have a rest period in darkness. This rest period should be roughly six hours.
Light intensity and type is another growth factor when growing indoors. When seedlings do not receive enough light, they develop leggy growth rather than compact growth. While more light is typically better, the type of light is also important. Diffuse light is more conductive to plant growth because diffuse light, unlike direct light, bends around corners. Think of each of a plant’s leaves as a solar collector. You can see how important it is to direct as much light as possible to the leaf surface of as many leaves as possible. Direct light impacts the upper canopy of the plant but leaves the rest of the plant in shadow. Since a plant is able to convert both direct and indirect light energy into food, the amount of light touching the leaf surface directly influences how much food the plant produces and thus the growth rate. If plants are grown indoors without a natural light source, grow lights perform best when placed a few inches from the seedlings. That said some grow lights produce much more heat than others. High heat tends to dry out tender seedlings quickly. Metal Halide lights may be placed much further from the plant material than fluorescent lights, T-5 fluorescents and LED grow lights.
Heat
The last easily controlled element is heat. Seedling leaves are extremely tender and easily damaged by frost. When planting indoors, frost is not a problem so seedlings tend to get a jump start because they can be planted indoors while there is still frost or even snow on the ground. By the time spring comes, plants transplanted are already established and are much more equipped to handle temperate shifts. Most plants can survive with temperatures down to the 40°’s, and will actively grow with night time temperatures of 55° and above. While the upper portion of the plant can handle cooler temperatures, roots like heat so adding heat develops and promotes rapid root growth. Many spring plantings are delayed, not due to the ambient air temperature, but due to the soil being too cold to plant. Seeds planted in cold soil often do not survive while root structures develop much more quickly with heat.
Bottom heat is most commonly used for seedlings. Bottom heat is applied directly to the rooting area where it’s needed most. Cooler air temperature and warmer soil makes for strong root development and healthy compact growth. With compact growth, the plant is able to produce more light collecting leaves in a smaller area. The roots and stem have to work less to get nutrients to all areas of the plant.
In a greenhouse, temperatures may vary significantly more than other indoor climates. Depending on the insulation provided by the greenhouse covering, the greenhouse may hold heat all night, or may not retain any heat as soon as the sun sets. This will be an important consideration in determining your heating strategy. If your night time temperatures are moderate, using heat mats to heat the bottom of the trays may be all you need to maintain a growing temperature. If you are starting many seeds at once, it may be cost effective to build your own propagation box using heating cables and sand. If your air temperature is dropping below 40°, consider adding supplemental heat to maintain growing temperatures. You can monitor the greenhouse nighttime temperature easily by using a simple min/max thermometer. There are inexpensive manual and digital versions available. More complex systems allow you to monitor your greenhouse temperature from your home.
As a side by side test, in late November we planted two trays of lettuce in a primarily coir media and after a few days, both trays germinated and were actively growing. We placed one tray inside under a T-5 grow light and the other in an unheated greenhouse using LED grow lights for supplemental lighting. Both lights are set to come on for a few hours in the morning, and a few hours in the evening. Although temperatures dipped to the low 30°’s outside, the lettuce in the greenhouse is outperforming the indoor lettuce. The growth is thicker and substantially larger in the greenhouse. One reason for the increased growth may be the diffuse light provided by the covering rather than direct light from the grow light. The greenhouse is also insulated so the inside temperature is remaining warm enough to foster growth. This experiment was not a scientific one, so we are unsure what one variable contributed most to the different growth, however, we will continue to use the greenhouse for our seedlings.
When I checked on the project last it had been dark for a few hours already. The outside temperature was 35° but it was comfortable inside the greenhouse providing a warm growing environment. It was interesting to see the significant difference in growth between the lettuce grown indoors and that grown in an unheated greenhouse. Experimenting like this is an important way to determine what will work best for what you like to grow. Sometimes making even one small change can have a major impact on the speed of growth.
When deciding whether to plant your seeds indoors or in a greenhouse, consider the convenience. Young seedlings need a constant supply of water so it’s a good idea to check on them frequently. Placing tender seedlings in an inconvenient place is a way to lose them. One busy day could spell the difference between success and seedlings that don’t make it. While a greenhouse environment is ideal, it must also be practical to access. Space is another consideration. Many gardeners find they run out of space to start seeds indoors. Operating grow lights inside and juggling trays can take up a great deal of prime real estate. If you are getting a little crowded, a greenhouse may be the saving grace as there is generally only so much counter space our families will allow us occupy.
However you decide to start your seeds, you will find the process rewarding if you pay attention to the light, heat and moisture. As you try different methods, you will find what works best for you, and you will learn about the needs of the plants in the process. Starting your own plants from seed is one of the most economical and rewarding parts of gardening. When you have a greenhouse, not only do you get a jump start on the season, you will see the first signs of spring, long before there is life stirring around you.
Michelle Moore is the General Manager of the Greenhouse Catalog where she has worked with greenhouses for 20 years. Michelle writes and lectures about greenhouse gardening as an Oregon State University Master Gardener and member of Garden Writers Association. Michelle is a Fulbright Scholar and earned an International MBA from Thunderbird, School of Global Management. Michelle and her husband live in Oregon, but they enjoy hints of summer all year in their greenhouse!
Michelle.Moore@GreenhouseCatalog.com
or www.GreenhouseCatalog.com/garden.
[i] Botany for Gardeners, revised Edition. Brian Capon. Timber Press 2007
