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How to Start Seeds Indoors

How to Start Seeds Indoors to Transplant Outdoors

Read our article on how to start seeds indoors for outdoor transplanting. Learn about the tools and materials you will need to create an ideal environment for your young plants. After starting your seeds indoors, learn how to harden off your seedlings to transplant your seedlings outdoors.


These practical tips that will guide you through the entire process of how to start seeds indoors and successfully transitioning them to your outdoor garden.


SEEDS

You will want to start most garden seeds 6-8 weeks before the last spring frost. Find your last spring frost date HERE.


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Each seed packet will list the days to maturity. Keep in mind that for seeds directly sown into your garden, this is from planting date. The maturity date for seeds started indoors is the date from transplanting.


SEED TRAYS

Select a suitable container for your seeds. Start vegetables in their final containers to reduce root disturbance. Flowers can begin in smaller containers to save space.


Use a seed container & tray to make it easy for you to transplant your seedlings.


32 Cell Seedling Tray Insert

Kickstart your germination with the use of bottom heat mats. Most seeds germinate better in warmer soil. Use a seed tray heating pad to maintain the temperature at 68 - 86 F, which boosts germination rates and prevents damping off.


Sunpad Seed Tray Heat Mat

SOIL

Use a good quality potting soil. Extra nutrients aren't necessary until your seeds sprout, after which you'll need to move these seedlings to a larger container.


I recommend my soil mixture from Square Foot Gardening. Read more about the perfect soil for seedlings here.


Perfect potting soil mixture that is homemade

SOW YOUR SEEDS

Follow the seed depth on the packet or plant seeds at a depth 4 times their width if not listed. Sow 2-3 per cell and then thin to 1 after germination, if needed. Thinning means to remove the extra seedlings so they do not crowd the small cell.

Sow a cucumber seed into the potting soil of the seed tray inserts

I like to use Seed Tape for small seeds such as carrots. Read more about how to make your own Seed Tape HERE.


Some seeds will need to be soaked to soften the seed coat. Do a little research on the seeds you're planting from the manufacturer's website.


WATER

Seedlings need consistent watering directly on the soil to thrive, keeping it as damp as a sponge. Avoid wetting the leaves.

Cucumber seedling holding on to seed shell as it sprouts

Insufficient water causes wilting, and water is vital until seedlings are established.


Monitor the soil drying out when using heating mats and with rising spring temperatures.


LIGHTS

Light is very important. If you're growing indoors you may need grow lights.


Your seedlings leaves need light as soon as they emerge. This allows them to store and use energy beyond seed reserves and strengthens their stems for transplanting.


Position the grow lights approximately 2-4 inches above the tops of your plants, operating on 12-16 hour cycles. As the plants develop, adjust the grow light to keep the 2-4 inch distance.

LED grow lights have full spectrum lighting that plants need

To cultivate multiple trays indoors, consider building a growing rack equipped with adjustable LED light strips.


Growing rack built from wood that has LED full spectrum grow lights

HARDEN OFF

Hardening off your seedlings is an important step you cannot afford to miss. When the weather warms up to over 45 degrees, start to get your seedlings used to the outdoors through a process called hardening off.


Start by placing them outside for one hour on the first day, then bring them back inside. Increase their outdoor time a little bit each day, until they can stay outside all day before transplanting.

This helps young plants develop resilience to temperature changes.


Harden off seedlings before transplanting outdoors

TRANSPLANT

Once your plants are hardened off, it is time to transplant them outdoors.


Prep your garden soil and amend it, if needed.

Dig a hole twice as wide as the transplant and deep enough to bury the roots. Carefully take the plant, with its soil, out of the transplant container. Gently loosen the root ball and place it in the ground. Tamp down the ground around the transplant and water it thoroughly.


Transplant tomato plants into outdoor garden area after hardening off

A few more tips for transplants:

  • If frost is expected, cover your new transplants until they establish roots in their new spot.

  • If temperatures rise, make sure they receive sufficient water throughout the day.


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