How to start seeds indoors

How to start seeds indoors, the supplies needed, choosing the best location and how to care for healthy seedlings.

How to start seeds indoors:

1. Choose location & set up growing space
2. Gather supplies
3. Soil & planting seeds
4. Caring for seedlings
5. Transplanting to larger containers
6. Hardening off before final planting

1. Choose location & set up growing space

Seeds need light and warmth to germinate. Choosing the location where you will set up your growing space is a crucial element for seed-starting success. Spaces that receive 12-14 hours of consistent light are necessary to avoid “leggy” seedlings. Leggy seedlings struggle to create a strong root system. They can be prone to falling over, weak, and struggle to produce foliage.

If you are going to be using grow lights, you will have a little more flexibility in this area. Temperature is also a factor when germinating seeds. The ideal temperature is 70-80°F. Seed starting mats are helpful with this, especially if you live in a drafty or cooler home that doesn’t maintain a consistent temperature.

I don’t have much space to work with in my small, wood-heated home. I start seeds in a dark and drafty corner in my dining room. To provide the most ideal environment for seedlings, I have a cheap indoor greenhouse, seed heat mats, and grow lights that I zip tie to the shelves. This provides light and warmth, as well as vertical shelving to save on space. My setup isn’t pretty, but it works perfectly for me, and wasn’t a large cost investment.

2. Gather Supplies

Essential to seed starting is seedling starting trays or pots, seed starter mix, labels, light, and warmth.

• Plastic strawberry or greens containers from the grocery store can be used before purchasing starting trays. Whatever you choose, make sure there are drainage holes in the bottom, and a tray underneath. You will want to ensure is sturdy enough that it won’t disrupt delicate root growth.
• Seed starter mix is not the same as potting soil. It contains matter that allows for better root development and moisture retention. Seed starting mix can be found anywhere you purchase potting soil.
• Labels are necessary for noting what seedlings are what, especially when starting multiple types of plants in the same tray. Labels can be purchased, but they are not necessary. Popsicle sticks can be used, or cut old yogurt containers into strips. Those little seedlings can all look very similar, and you won’t want to mistake them when planting in the ground!
• If you do not have a well lit, warm space for your seedlings, you will need to purchase grow lights and heat mats. These will be more cost up front, but will be a one-time purchase that will pay off year after year in healthy, strong seedlings. I have purchased inexpensive ones off amazon, and they have lasted for years.
• Items that are nice to have, but not necessary: indoor greenhouse or wire shelving, timer for grow lights, water sprayer (I prefer this over a watering can, as it doesn’t disrupt needs on top of the soil,) fan for air circulation, and vermiculite.

3. Soil and planting seeds

Seed starter mix is not the same as potting soil. It contains matter that allows for better root development and moisture retention. Once your seedlings are established and ready to be potted in larger containers (this is called “up-potting”) you’ll want to switch to potting soil. This will be my first year using vermiculite in addition to potting soil. Vermiculite holds water while still allowing proper drainage, keeping seeds from drying out but preventing waterlogging, and reduces the risk of fungal diseases and pests. This is especially important if your soil is too damp or there is too much humidity.

Pre-moisten your soil until you can squeeze a fistful and it holds together, but is not dripping water. Fill your containers and lightly tamp down to ensure there are no air pockets.

Follow the instructions on your seed packet for seed depth. Placing two seeds per cell increases the chance of successful germination. If both seeds sprout, they can later be separated into their own cell or pot. This is also a good opportunity to choose the plants that are looking the most strong and healthy.

4. Caring for seedlings

Seeing tiny little seedlings pop up from the soil is an exciting feeling! Those tender seedlings require special care to mature into strong and healthy plants.

Seedlings require 12-14 hours of close light each day. If the light isn’t closely above them, they will become “leggy” and weak by trying to reach for the light. I start with my lights close to the soil, and then move it up after they have sprouted. I use zip ties for this, but many grow lights come with chains for this purpose.

After they have sprouted, remove the cover or humidity dome. They will need air flow to prevent fungal growth. A fan will help with airflow and strengthen plants.

Use caution when watering. I prefer to use a sprayer to mist the soil. I like having more control than with a watering can. Some people water from below when using a seed starting tray. Whatever method you choose, use caution not to overwater and drown the seedlings, or create soil so wet that mold develops.

If multiple seedlings germinated per cell, gently separate and plant them, or dispose of the less healthy seedlings. Crowding will not create strong plants.

5. Transplanting to larger containers (“Potting Up”)

Seedlings often need to be transferred to a larger container to grow before planting outside. Up potting your seedlings prevents them from being root bound and allows for nutrient absorption before hardening off and being planted outdoors.

Choose a larger pot or cup. I save all of my pots from plants purchased from the nursery, or use large plastic cups with drainage holes poked into the bottom. Fill with dampened potting soil, and gently plant your seedling. Don’t forget to label each plant! Water gently and apply fertilizer.

6. Hardening off before final planting

Hardening off plants is the process of gradually exposing indoor-grown seedlings or greenhouse plants to outdoor conditions before transplanting them permanently. This helps them adjust to changes in temperature, sunlight, wind, and humidity, reducing transplant shock and increasing their chances of survival. Begin about 7–14 days before transplanting. Place plants outside in a sheltered, shady spot for a few hours each day. Gradually extend their time outside and introduce them to more direct sunlight and wind over several days.

You should not skip hardening off your seedlings. Your plants can scald in the sun or break off in the wind if they haven’t been given a chance to strengthen slowly outdoors. Always keep a close watch on the weather when hardening off and then planting. It’s tragic to lose all your hard work to a sudden overnight frost or afternoon hail storm!

Conclusion

Learning how to start seeds indoors is rewarding and can lead to large harvests when following these simple steps. You shouldn’t be afraid to get creative with the supplies you use to get started. Gardens have been grown for hundreds of years without fancy or costly equipment. Supply your seeds with the right environment and follow their growing instructions, and you will be rewarded!

Comment below your favorite seeds or variety of seed that you are starting this gardening season! If you need more help with getting your garden space set up after learning how to start seeds indoors, check out my post “How to plan a garden for beginners.”