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Starting Seeds Indoors

Below are the basic requirements for your project. At the bottom of the page, you will find a chart with recommended starting times.

Seed Starting1. Light
For seeds to sprout, they require either a south-facing window or grow lights that have been placed about 2 inches overhead. Use a timer to ensure that seedlings receive 12-14 hours of light per day. Give the containers a quarter-turn daily to provide even sunlight. 

2. Containers
You can buy or recycle containers for seed starting. Just note that they need to be at least 2-3 inches deep, thoroughly cleaned, and poked with drainage holes. For an eco-friendly/budget-friendly option, reuse containers on hand, such as yogurt cups, pint-sized milk containers or cottage cheese tubs.

Peat PotsSeedling trays, peat pots and peat pellets can be purchased at your local garden center.Another option is to plant your seeds in rows in a wide, shallow flat; this is a smart option when broadcasting fine seeds, such as lettuce.After 6-8 weeks, seedlings can be separated and replanted into individual containers.Seedlings are happiest at this stage, when they have room to spread out their roots!

Garden Hints Garden Hint
It is a good idea to sterilize containers that have been previously used for seed starting, just in case. Soak them in a 10% bleach-water solution for 15 minutes, air dry, and you are good to go.

3. Seed Starting Mix
To start your seeds, you will need a much lighter and spongier planting medium than the soil you find in your backyard. Use a commercial seed starting mix purchased at your garden or home improvement store - it will be sterile and will not introduce any disease-causing organisms from the garden. You can also make your own mix, combining 1 part each of perlite, vermiculite and sphagnum moss. Be sure to dampen mix thorougly in a small bucket before filling your containers and planting the seeds.

4. Moisture
Some seed trays come with plastic transparent covers that allow light in while keeping the soil moist. You can also simply use plastic wrap, or clear plastic bread loaf bags. When using any of these methods, be sure to monitor your trays - if you see mold or fungus growing due to excess moisture, remove the plastic cover and let your seedlings "breathe." You may also use an electric fan, kept on low, to keep air circulating around your seedlings. As soon as sprouts emerge, stop using the plastic covers.

To maintain even moisture and avoid the onset of disease, monitor daily. Also avoid overwatering - let the planting medium dry out before re-dampening.

5. Seeds
If you want to grow plants from your own seeds in future seasons, be sure to choose parent or heirloom seeds - hybrid seeds will not produce the same plant in years to come. Quick germinating vegetables such as radish and lettuce are a good choice in a classroom. It is always a good idea to read the package instructions thoroughly when starting your germination project. On the back of most seed packages you will find zone information, as well as sun, soil and watering requirements.

6. Temperature
Germination temperatures listed on seed packets refer to soil temperature, not air temperature. Most seeds prefer a temperature of about 75 degrees, but can fall within the range of 65-80 degrees. In a classroom, consider placing your containers near a heater - just be sure to check daily, making sure they don't dry out.

Warmth is key to the germination process - if the soil is too cold, your seeds may never sprout. This is why greenhouses are ideal locations for starting seeds; however, you can still create ideal conditions with the use of grow lights or heat mats. Home gardeners have found other ways to ensure continuous heat for their baby plants by placing their trays on top of the fridge, the oven's pilot light, or even the television set!

Grow LightOnce your seeds have sprouted, make sure to get them under a grow light or in a sunny window right away. At that point, seedlings grow best if the air temperature is below 70 degrees fahrenheit. If temperatures are too warm (over 75 degrees), the seedlings will grow too fast, and become weak and spindly.

When to Start
Even when frosty mornings are long gone, you still need to put vegetables in the ground when the temperatures suit them. Refer to the chart below for guidance. Cool weather crops are hardy in northern climates during the spring and fall months, while warm weather crops should be set in the ground during the summer.See individual seed packaging for more information!

It is key that you start your seeds according to the last frost date in your region, so that you can properly time your indoor project with your outdoor planting - click here to locate the frost dates in your state. You want your seedlings to be ready to plant in the ground at the optimum time for their growth, and so starting seeds too early can leave you in a bind.

Cool Weather Crops Germination Period When to Start Seeds
Lettuce 7-10 days 5-6 weeks before planting outdoors
Radish 5-7 days 5-6 weeks before planting outdoors
Broccoli, cabbage, collard greens, cauliflower 7-10 days 5-6 weeks before planting outdoors



Warm Weather Crops Germination Period When to Start Seeds
Peppers 14-20 days 8-12 weeks before last frost
Tomatoes, eggplant 8-10 days/7-12 days 6-8 weeks before last frost
Melon, cucumber, squash 5-10 days/7-12 days 2-4 weeks before last frost

 

Flowers
Germination Period When to Start Seeds
Nasturtium, morning glory 7-14 days/12-21 days 4 weeks before planting outdoors
Bachelor buttons, marigolds 7-14 days/7 days 6 weeks before planting outdoors