How to Germinate Seeds: All the Basics of Seed Starting Indoors

You can give your flower and vegetable garden a head start and save money by knowing how to germinate seeds. With the right amount of heat and moisture, starting seeds indoors is simple.

When the seedlings emerge, be sure that they have a good light source and a warm spot to continue growing. Soon, you'll have plants ready to transfer to the garden or a container.

Learn all the basics of germination and seed starting indoors below.

What Is Germination?

Germination of seed begins when moisture uptake activates the metabolic pathways stored in the seed to produce a plant. Dormant seeds need water, oxygen, and proper temperatures to germinate and allow the seed coat to break open and the root to emerge. 

Once the root is established, a shoot that contains the stem and leaves will appear and require sunlight to thrive.

How to Germinate Seeds in a Paper Towel

If you are in a hurry to see if the seeds you saved from last year will germinate or if you want to teach others about germination, all you need is a paper towel, water, a sealable plastic bag or container, water, a permanent marker, and seeds.

Here's how:

1. Moisten the paper towel. Wet the paper towel, wringing out excessive water, and lay it flat.
2. Lay the seeds on the towel. Place several seeds in neat rows on half of the paper towel and fold the other half over the seeds.
3. Place the paper towel in the plastic bag. Seal it to prevent the towel from drying out.
4. Label the bag. Write down the plant name and the date.
5. Keep the bag warm. Be sure to place the bag in a warm area with a steady temperature of around 70 degrees Fahrenheit.
6. Check the seeds periodically. After three or four days, check the seeds to see if they need more moisture. Most vegetable and flower seeds germinate in seven to 10 days. If you have purchased seeds, the packet often lists how many days it takes for seeds to germinate.

How to Germinate Seeds in Soil

While using the paper towel method to germinate seeds is interesting and easy to do, it is usually not the best method for producing strong seedlings. If the seeds are left too long in the paper towel, the tiny, hair-like roots grow into the paper towel fibers and are damaged during transplanting slowing or preventing a seed from maturing into a strong seedling.

The quickest way to germinate seeds in soil is to be sure they have good contact with the seed-starting mixture, sufficient humidity, and lots of warmth. Heat mats placed under the seed starting tray are an excellent way to give the seeds a quick start.

1. Prepare the seed starting medium and container. Choose a commercial seed-starting mix and moisten it well. Fill the container to within 3/4-inch from the top. The mixture should be level and firm without air pockets.
2. Sow the seeds. If you are using a seed-starting tray with individual cells or small individual containers, place two or three seeds in each cell or pot. If the container is a large flat, sow the seeds uniformly in rows about 2 inches apart.
3. Label the seeds. This is especially important if you are sowing different types of seeds in the flat or seed-starting tray.
4. Lightly cover the seeds. Cover the seeds with enough dry vermiculite or seed-starting mix to equal two times the diameter of the seed. Very tiny, fine seeds are usually left uncovered. Lightly pat down the soil.
5. Moisten the surface. Use a mister or spray bottle with water to lightly moisten the surface of the seed tray or containers.
6. Capture the moisture. Place the lid on the seed starter tray or cover the container with plastic wrap or a plastic bag to create a mini-greenhouse. Capturing the moisture means that no additional watering should be needed until after the germination of the seeds.
7. Keep the seeds warm. Place the covered container in a warm place (65 to 75 degrees Fahrenheit) or a heated seed-starting mat.
8. Watch for seedlings to emerge. At the first sign of green shoots, remove the lid or plastic covering and place the container in a bright south-facing window. The seedlings need lots of light to flourish. Alternatively, use a grow light.
9. Maintain moisture levels. Allow the seed-starting mixture to dry out slightly between waterings but do not allow the seedlings to wilt. Do not overwater and do not allow water to stand in the containers or else the seedlings will dampen off (rot).
10. Thin the seedlings. If every seed germinated and the seedlings are crowded, use garden snips to remove the excess at the soil line. Most seedlings should be transplanted to individual/larger containers when there are three sets of leaves on the stem.

What Seeds Can You Start Indoors?

Vegetables and Herbs

• Tomatoes
• Peppers
• Eggplants
• Broccoli
• Cabbage
• Brussels sprouts
• Cauliflower
• Head lettuce
• Okra
• Dill
• Basil
• Mint
• Sweet potatoes

Flowers

• Ageratum (Ageratum houstonianum)
• Snapdragon (Antirrhinum majus)
• Wax begonia (Begonia x semperflorens-cultorum)
• China aster (Callistephus chinensis)
• Vinca (Cathranthus roseus)
• Cockscomb (Cleosia spp.)
• Bachelor's button (Centaurea cyanus)
• Cosmos (Cosmos spp.)
• Lisianthus (Eustoma grandiflorum)
• Globe amaranth (Gomphrena globosa)
• Strawflower (Helichrysum bracteatum)
• Impatiens (Impatiens wallerana)
• Annual statice (Limonium sinuatum)
• Melampodium (Melampodium paludosum)
• Four o'clock (Mirabilis jalapa)
• Flowering tobacco (Nicotiana alata)
• Geranium (Pelargonium x hortorum)
• Petunia (Petunia x hybrida)
• Moss rose (Portulaca grandiflora)
• Black-eyed Susan (Rudbeckia spp.)
• Red salvia (Salvia splendens)
• Mealycup sage (Salvia farinacea)
• Creeping zinnia (Sanvitalia procumbens)
• Coleus (Plectranthus scutellarioides)
• Dahlberg daisy (Thymophylla tenuiloba)
• Zinnia (Zinnia elegans)
• Verbena (Verbena x hybrida)
• Bells of Ireland (Moluccella laevis)
• Candytuft (Iberis sempervirens)
• Cleome (Cleome)
• Dianthus/pinks (D. plumarius)
• Hollyhock (Alcea spp.)
• Phlox (Phlox)
• African marigold (Tagetes erecta)
• Morning glory (Ipomoea purpurea)
• Sweet pea (Lathyrus odoratus)
  

What Seeds Should Not Be Started Indoors?

Vegetables

Some plants mature quickly enough that starting seeds indoors is not necessary. Beans, corn, peas, spinach, leaf lettuce, kale, pumpkins, melons, and squash can be direct-seeded in the garden or outdoor container.

Root crops do not transplant well from seed-starting trays. Direct sow carrot, radish, kohlrabi, beet, and turnip seeds. Seed potatoes (potato eyes) should be planted directly into the garden or a container.

Flowers

Nasturtium (Tropaeolum majus) and sunflowers (Helianthus annuus) do not transplant well from a seed-starting tray. If germinating the seeds indoors, they should be started in biodegradable pots that can be directly planted into garden soil.

Additional Tips for Successful Seed Germination

• If reusing containers to germinate seeds, clean and sterilize them before using. Wash the containers in warm, soapy water and then dip them in a solution of one part chlorine bleach and 10 parts water. Allow them to air dry completely before adding the seed-starting mix.
• Do not use garden soil for seed germination. It is too heavy and the seeds will have a difficult time sending down roots and sending up green shoots.