How to Start Seeds Indoors

Growing flowers and vegetables from seeds gives you more options when you’re looking for varieties to plant. For example, it’s often easier to find seeds for your favorite heirloom tomatoes, rather than seedlings. Plus, depending on the size of your garden, growing from seeds can save you money, especially if you’re planting a large vegetable garden or growing a flower garden with annuals and perennials.

Steps for choosing seeds:

• Start by growing what you love. List your favorite flowers and vegetables that can be grown from seed. Edit your list based on your allotted garden space and the seasons that you're growing in.
• Understand your site’s light. Most annual vegetables and flowers grow best in full sun, defined as at least 6 to 8 hours of sunlight each day. If your site gets less than six hours of light, you’ll need to look for shade tolerant seed varieties.
• Next, learn your area’s average dates of first and last frost. The last frost date in spring tells you when you can safely transfer plants from indoors to outdoors.
• Seed packets will tell you when to start seeds. For example, “start seeds indoors 4 to 6 weeks before the last spring frost in your area.”

Keep in mind that if you start too early, seedlings will become leggy and weak while you're waiting for warm temperatures for transplanting. If you start seeds late, you can miss out on ideal conditions for flowering and fruiting. Changing weather patterns make timing challenging each year, but with practice year after year, you’ll get better at timing your seed starting.

Tip: In the Garden Center and online, seeds are always fresh, non-GMO and packed for the current season.

Choose a place indoors to set up your seed starting project. The ideal space will have lots of light and room to set out the trays.

Tools for Seed Starting:

• Bucket
• Trays or peat pots
• Small trowel
• Soil scoop
• Plant labels
• Permanent marker
• Humidity dome
• Heat mat
• Spray bottle
• Pencil (use eraser to press small seeds into soil)
• Grow lights, optional
• Shelves, optional
• Soil blocker, optional

Gardeners use a variety of cups, pots and trays for seed-starting. You can buy seed-starting kits that have all the pieces you'll need. You can also use materials from around your home. If you're using disposable cups, make sure they're clean and they have plenty of drainage holes in the bottom. Place cups in a tray to help make watering easier.

Materials for Seed Starting:

• Soilless seed starting mix
• Seeds

Seeds need a fluffy, well-draining potting mix for the best start. In the Garden Center and online, look for products labeled for seed starting. You can create your own seed starting potting mix using heat-treated soil or compost, either peat moss or coconut coir for moisture retention, and sand, vermiculite or perlite for drainage.

Ventilated shelving is useful for setting out lots of trays. Learn how to set up a DIY grow light station.

Tip: Starting seeds in eggshells is a popular and cute idea, but the size of shell and lack of drainage holes are problems. You'll get best results by using cups with drainage holes.

Your growing media is important for seed-starting success. You don't want to use garden soil (and especially not dirt) for seed-starting. Regular garden soil is too heavy, compacts too easily and carries weed seeds and pathogens that can harm tender seedlings.

The best choice for starting seeds is a sterile, soilless mix. These mixes are lightweight, fluffy and formulated to hold the right amount of water while allowing air to reach the roots.

You can make your own seed-starting mix using these ingredients:

• Sphagnum peat moss or coconut coir soak up and hold moisture, keeping your seeds hydrated.
• Vermiculite is a natural mineral that helps retain water and nutrients while creating air pockets that allow roots to breathe.
• Perlite is made up of small, white, lightweight particles that improve drainage and keep the mix loose, so it doesn’t get compacted.

Seed-Starting Mix Instructions:

• In a bucket, place peat moss or coconut coir and add water.
• Stir well, until it is blended.
• Use your hands to check that the mixture is not soggy. When you squeeze a handful, it should hold its shape without dripping water.

Sowing seeds in pots and trays is easy. Here are the steps:

• Begin by preparing the soil mix. Pour the soil mix into a bucket, add warm water and stir until moist, but not soggy.
• Next, fill pots or trays with the dampened soil mix to within ¼-inch of the rim.
• Tamp down the soil to reduce air pockets.
• Sow seeds according to package directions. Depth is usually two or three times the diameter of the seed.
• Use the tip of an eraser to gently push small seeds into soil.
• Use a permanent marker to label containers and trays with the seed variety and planting date.

Tip: Some seeds, like peas, benefit from an overnight soak to loosen the seed coat before sowing. Check the seed packet for details on prepping seeds for sowing.

Soil blocking is a method that eliminates using seed-starting pots. Instead, you use a soil block maker to form soil into stand-alone blocks that serve as both container and growing medium. Soil blocks promote strong roots and reduce transplant shock, as roots are "air-pruned" when they reach the block's edge, preventing them from circling or becoming root bound.

For a successful soil blocking mix, experts recommend blending one part peat moss or coconut coir for moisture retention, one part perlite or vermiculite for drainage and one part compost or garden soil for nutrients. Avoid regular potting soil, which isn’t fine or cohesive enough for blocking. The mix should be evenly moist, like wet oatmeal, so it sticks together but doesn’t drip when squeezed.

Follow this method to make soil blocks at home:

• In a basin, large bowl or bucket, combine peat or coir, perlite or vermiculite and compost. Add water gradually until the mix is damp but not soggy.
• Firmly press the soil blocker tool into the mix several times, packing it well to form solid blocks.
• Place the loaded tool over a waterproof tray and push the plunger to eject blocks about 1/4-inch apart.
• Plant the blocks by placing one or two seeds into the indentation on each block, following recommended depth (about twice the seed's width).

When you water soil blocks, be sure to pour water in the tray and not over the blocks. Allowing blocks to soak up moisture helps preserve their structure.

Tip: Soil blocking takes practice. Adjust the moisture and ingredients until the mixture holds.

After seeds are in pots or trays, keep them in a moist, warm environment to encourage germination. Use a spray bottle set to "mist" to gently spray newly planted seeds. Gardeners use humidity domes to help the seeds stay moist. You can also use clear plastic bags. Just be sure to open them from time to time to check on your seedlings.

Seeds need warmth for germination, and that can be difficult in a cool, dry home in winter. You can try putting the seed trays on top of a refrigerator or radiator. If you have more than a few trays, it’s best to use special heat mats to keep your seedlings consistently warm.

• When seedlings emerge from the soil, let air in by slightly venting the bag or dome.
• When the second set of leaves, called true leaves, emerge, you can remove the cover to let the seeds grow.
• Fertilize the seedlings each week using a water-soluble fertilizer added to the watering tray.

To help the seedlings grow, position grow lights 6 to 12 inches above the seedlings and keep them on 12 to 16 hours each day.

To grow strong seedlings, you need to provide the right kind of light. A good grow light acts as a substitute for natural sunlight, driving photosynthesis to produce healthy plants ready for your garden.

For starting seeds at home, the most common lighting options are fluorescent and LED. A dedicated LED grow light will deliver a full spectrum of light that closely mimics sunlight.

The color of the light is important for plant development. Blue light helps with essential leaf and vegetative growth. Red light is more important later in a plant’s life to encourage flowering and budding.

Some LED fixtures offer adjustable light spectrums that allow you to switch between a blue-white light for early leaf growth and a red light for flowering.

Many gardeners successfully use standard fluorescent shop lights for seed starting. Cool-white fluorescent tubes are an inexpensive option that provide the blue-spectrum light seedlings need. For best results, keep the lights on for 16 to 18 hours daily.

Setting up your grow light system is straightforward:

• Suspend a shop light or grow fixture with chains so you can easily adjust the height.
• Position the lights 4 to 6 inches above the seedlings.
• Raise the lights as the plants grow, maintaining a close distance to prevent leggy growth.
• For consistency, use a timer to automate the light cycle.

In early spring, harden off seedlings by gradually introducing them to outdoor conditions. Hardening off helps seedlings adjust to wind, sunlight and temperature changes.

Follow these steps to harden off seedlings:

• Place trays outside, but not in direct sun or high winds, for a few hours at a time, before bringing them back inside.
• Gradually build up the outside time to include overnights.
• You can use a cold frame or portable greenhouse to help harden off seedlings.
• After acclimating, seedlings are ready for their outside planting place.

You can safely plant your seedlings in spring when you’re past the average date of last frost.

Steps for planting seedlings in ground:

• Choose an overcast day and plant in early morning or late afternoon.
• Prepare garden bed by loosening up the soil and adding compost.
• Water the soil and seedlings before planting.
• Add vermicompost or slow-release fertilizer to planting hole.
• Gently pull seedlings from containers and place in soil.
• Finish with more garden soil and mulch, if using. Mulch helps plants retain moisture and protects new roots from extreme temperatures.
• If rain is not in the next day's forecast, gently water in your newly planted seedlings.

Tip: You can re-use plastic trays and pots for future seed starting projects. Wash with a mild bleach solution to kill bacteria and store in a cool, dry place until you’re ready to plant again.