If you want an ornamental garden teeming with a variety of colored flowers or a vegetable garden overflowing with unusual varieties of crops, chances are you will need to start plants from seeds rather than simply purchasing transplants. Starting plants from seed gives you greater access to a wide variety of species, varieties and cultivars found in seed catalogs and from garden centers.
Starting Seeds Indoors
Some plants require a longer growing season, and seeds should be started indoors for maximum productivity. The seed packet will instruct you whether to begin seeds indoors or outdoors.
You will usually calculate when to plant seeds indoors based on your area's average frost-free date. Once you know your frost-free date, consult the seed packet to learn the number of weeks before that date you should begin your seeds.
You will need containers and seed starter or potting soil. While garden centers carry containers or pellets designed for starting seeds, any paper or plastic container that will hold soil will work. If you are planting large numbers of a single seed type, you can fill a shallow cardboard container or planting tray with seed starter and plant the seedlings in rows.
The growing medium, however, is not the place to save money. Always purchase a growing medium -- either a seed starter mixture or sterile potting soil -- rather than using soil from your garden, which can contain microorganisms that cause disease in seeds or seedlings. Also note whether the growing medium contains fertilizer. If it does not, you will need to purchase and add fertilizer separately, or your seedlings will not have adequate nutrients to properly grow.
To plant your seeds, fill the container with growing medium and press it gently with your hand to make it firm. Consult the seed packet to learn how deep to plant the seeds, the number of seeds plant and, if you are using a tray instead of individual containers, the space to allow between plantings. Always follow these instructions precisely, and don't try to crowd your seeds to save space. Seeds and seedlings vary in the amount of light they require, and not following planting instructions may prevent germination or slow the growth of the seedlings.
Starting Seeds Outdoors
Some seeds can be sown directly into the garden. The seed packet will inform you as to planting depth, spacing, the number of seeds to plant and any other special instructions. Once seedlings emerge, cut or pinch off all seedlings but the strongest ones so that your plants will not have to compete with each other for light, water and nutrients.
Seeds are covered with a hard coating or testa that can protect the embryonic plant within for years, until ideal conditions for germination develop. In the wild, natural forces help to soften or erode the testa. Most common vegetable and flower seeds do not require pretreatment; pretreatment is more common for seeds gathered from wild plants. When planting wild seeds with particularly hard coatings, gardeners use pretreatments that soften and allow water to penetrate the testa. The seed packet will specify which, if any, pretreatment to use.
- Soaking. Place seeds in water heated to 200 degrees Fahrenheit and allow them to soak overnight. Plant the seeds immediately and keep the soil moist.
- Mechanical scarification. Use a file to scrape away or a sharp knife to nick the seed coat.
- Acid scarification. Place seeds in a glass container and cover them with vinegar, stirring the seeds periodically, until the seeds soften.
- Stratification. Store seeds in a moist medium such as peat or sand. The amount of time and the temperature for stratification varies depending on the species.
Caring for Seeds
Water is essential to start the germination process. Rapid absorption of water causes the embryo to swell, crack through the seed coat and begin to root in the soil. Whether you start seeds indoors or sow directly into your garden, you should water the seeds thoroughly after planting and ensure the soil is kept moist until germination occurs.
Seeds vary as to whether they need light in order to germinate. Some seeds, such as lettuce (Lactuca sativa) and snapdragon (Antirrhinum species), need light in order to germinate. Others, such as pansy (Viola tricolor) and fennel (Foeniculum vulgare), require darkness. Always plant your seeds at the depth indicated on the seed packet. If you start seeds indoors that require a planting depth of less than 1/4 inch, make sure those plants have access to light.
Likewise, seeds vary in soil temperature requirements. Most seeds germinate best at soil temperatures of 75 to 80 degrees Fahrenheit. Temperatures below 60 degrees can slow down germination and leave seeds susceptible to fungal infections. When starting seeds indoors, it is generally best to keep the containers in a warm environment. For seeds that require warm soil temperatures, such as peppers (Capsicum species), a heating mat placed beneath the containers elevates the soil temperature and speeds up germination.
Caring for Seedlings
Most seeds germinate in a few days to two weeks. Once seedlings emerge, water and light become extremely important. Keep the soil moist and provide plants with access to abundant light by placing them in a sunny south-facing window or under grow lights. If seedlings do not receive enough light, they will become elongated and spindly, will not develop full-sized leaves and will eventually collapse and die.
After your seedlings emerge, you will need to thin them by removing all but the strongest seedling from each planting. Doing so improves the growth of your seedlings but ensures that they won't compete for resources. Use scissors to snip away the extra seedlings or pinch them off at the soil level.
Most seedlings can be moved outside after the average frost-free date in your area. A week to 10 days before transplanting your seedlings into the garden, you should begin to harden off the seedlings. On a windless day, move the seedlings outside for a few hours in a shady spot. This allows them to acclimate to outdoor conditions. Gradually expose the seedlings to longer sessions outdoors, wind and full sunlight.