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How to Start Seeds Indoors: 10 Steps for Success

Starting garden vegetables from seed has several advantages, but learning how to start seeds indoors can be overwhelming. I tried and failed several times trying to start seeds indoors. Each failure taught me something new. Learn from my mistakes and avoid making the same ones.

This article outlines the following steps:

  • How to start seeds indoors
  • How to care for the seedlings
  • What to do before planting them outside
  • Supplies you need to get started
How to Start Seeds Indoors: 10 Steps for Success

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Why start seeds indoors?

Some of the advantages of starting seeds indoors are: 

  • Seeds are often much less expensive than purchased transplants. 
  • There is a greater variety of options when you are starting from seeds.
  • When you grow from seed, you aren’t limited to planting what your local nursery or big box store has in stock. 
  • It’s exciting to have something growing inside when it’s too cold (or too hot) to garden outside. I love puttering with my seedlings and checking on their growth.
  • Plants grown from seeds can be planted at the optimal planting time for your location. Planting at the correct time is crucial for success. 
How to Start Seeds Indoors: 10 Steps for Success

10 Steps for How to Start Seeds Indoors

1. Decide where to start your seeds

I start seeds indoors two different times during the year; usually around JanuaryFebruary and again in JuneJuly. Outside or in a garage is too cold or too hot during those times of year. The ideal temperature for starting seeds is between 70-80°F. 

It’s nice if you have a greenhouse, but if you’re like me and don’t have one, don’t worry! I use my laundry room to start seeds indoors. I have a wire shelving unit that I keep in the garage other times of the year. When it’s time to start seeds, I move the shelving unit indoors. (Other times of the year it holds seed starting/gardening supplies in the garage.) 

2. Gather supplies for starting seeds indoors

This list may seem overwhelming, but most of these supplies are necessary. Start small, you don’t have to fill an entire shelving unit with seedlings. A grow-light on your counter with one seedling tray is just fine.

For the best chance of success starting seeds indoors, it’s important to have the right supplies to meet the basic needs of emerging seedlings

Here are the items I use in my seed-starting set up: 

1. Seeds – Use a planting guide or seed starting guide to determine which seeds to start indoors.  

2. Seedling Pots and tray – I love the ones from Bootstrap Farmer. They are nice and deep, and will last many years. 

3. 10×20 Seed Tray (without holes) – I love the ones from Bootstrap Farmer; they last a long time. You will put the seedling pots inside this tray.

4. Humidity Domes – Better quality ones will last many years.

Favorite Garden Tools & Supplies

5. Seed Starting Mix – Sterile bagged seed-starting medium. Do not use regular potting soil.

Favorite Garden Tools & Supplies

6. Light Source – T5 Fluorescent light works well for most seedlings. Get the right size for your seed trays and shelving. Light height needs to be adjustable to move up or down as seedlings grow.

Favorite Garden Tools & Supplies

7. Heat Mat – Helps to maintain a consistent ideal temperature while starting seeds. Optimum germination temperature is when the soil is 70-80°F.

Favorite Garden Tools & Supplies

8. Labels – Need to be small enough to fit inside the humidity dome when closed.

Favorite Garden Tools & Supplies

9. Fan – Make sure it is the right size to fit on your shelf with seedling trays. Seedlings need movement to develop strength, and to prevent disease, mold, and “damping off”. 

Favorite Garden Tools & Supplies

10. Power Strip – I use this one with a timer for the lights, and a regular one for the heat mats and fans. 

11. Watering Can – One with a longer spout makes watering indoors easier (and less messy).

How to Start Seeds Indoors: 10 Steps for Success

12. Syringe – Helps remove excess water from trays. 

Favorite Garden Tools & Supplies

13. Wire Shelving – Make sure the dimensions of the shelving will fit your seed trays and lights.

3. Get everything ready to go before you start your seeds

Before you plant the seeds, it’s important to have your indoor growing set up all ready to go. 

Set up your light, plug in the heat mat, and make sure everything fits and is working properly. 

How to Sanitize Seed Starting Supplies

Clean and sanitize your seed pots and trays. Read this blog post to learn more.

Spend a few minutes organizing your seeds and planning how many of each you will plant. Make labels for what you are planting in each of your seed trays. Making labels is much easier when your hands aren’t covered in soil!

How to Start Seeds Indoors: 10 Steps for Success

4. Fill containers with pre-moistened soil

Wet down seed starting mix and allow it to absorb moisture until it is damp but not overly wet. Holding containers over soil, fill them up completely while trying to avoid big air pockets. 

How to start seeds indoors

5. Plant seeds and add labels

How to start seeds indoors
  • Plant seeds according to package directions. Planting 2-3 seeds in each pot helps to ensure at least one will sprout. 
  • Press seeds into soil as you plant to ensure good seed to soil contact. 
  • Add labels as you plant.
How to start seeds indoors
  • Put domes on trays and place under lights on heat mats. Most vegetable seeds germinate best at soil temperatures warmer than typical homes. Adding a heating mat speeds germination and warms the rooting area which encourages root growth. Once seedlings emerge, they also benefit from the added warmth a seedling mat provides. A seedling mat automatically warms roots to 10-20°F above current room temperature. If your location is already 75-80°F, you may not need a heat mat. 
  • Mist seeds lightly if they dry out; it may not be necessary to water until seeds sprout if soil is moist enough. 
How to start seeds indoors

6. Remove domes, and provide light and airflow for growing seedlings

  • When about half of seedlings sprout, remove the humidity dome.
  • Adjust the light height as seedlings grow, always keeping the light within an inch or two of seedlings. Sprouting seeds expend all their energy to break through to the surface and need a new energy source. This is why providing bright overhead light is so important (light from a nearby window is seldom, if ever, enough). 
  • Not enough light leaves seedlings leggy, spindly, and unhealthy.
How to start seeds indoors
  • Use a timer to have light on for 12-16 hours each day. 
  • Use a fan to provide airflow for seedlings.

7. Water seedlings correctly when growing seeds indoors

  • Pay attention to your plants. Don’t let seedlings dry out, but they shouldn’t be soggy either.
  • Water the seed trays from below as needed with a watering can.
  • If there is still water in the bottom of the tray an hour or two after watering, you need to empty it. Carefully dump it out or use a syringe to remove the water.

8. Thin and fertilize growing seedlings

Once seedlings have true leaves, it’s time to thin and fertilize your seedlings. 

  • Thin to strongest seedling by clipping off smaller seedlings. (Bonus: eat them as microgreens!)
  • Fertilize lightly by adding a half-dose of seaweed fertilizer to your water once a week. 

9. Transplant into larger containers as seedlings grow

If it’s not time to plant outside and your seedlings are outgrowing their containers or roots are coming through the drainage holes, it may be time to repot your seedlings into larger containers. (Depending on the size of your seedling and container, this step may not be necessary.) 

How to start seeds indoors

“Potting up” seedlings allows them to stay in the ideal conditions of your seed-starting area until they can be planted in your garden.

Read this post for more information about when and how to pot up seedlings.

10. “Harden off” seedlings before planting outside

Plants go into transplant shock if they do not have time to adapt and adjust to the different conditions outdoors. It is important to harden off your young seedlings before planting outside. Check weather conditions and planting guides to determine when to plant seedlings outside. 

How to Start Seeds Indoors: 10 Steps for Success
  • Gradually wean plants off the heat mats. Begin by turning them off during the day and only keeping them on at night. Turn off the heat mats completely about a week before transplanting. 
  • Beginning a week before planting, put seedlings outside in a protected and shady location. Start with an hour or two, gradually working up to several hours. Towards the end of the week, allow them to be in the sun for at least part of the day. Bring them back indoors each night. Protect from birds with netting if necessary. 
  • Keep seedlings watered during this process. 
  • For spring planting, plant transplants in the morning so they have the entire day to adjust before the cooler temperatures at night. 
  • For fall and monsoon planting, plant transplants in the early evening so they have the cooler temperatures of nighttime to adjust before the heat of the day. 

How To Harden Off Seedlings

Read this post for more information about how to harden off seedlings.

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If you found this post about how to start seeds indoors helpful, please share it:


Monday 16th of January 2023

Hi! Thanks for creating this site! It is nice to read something that is clear and very well written and well thought out. You really know how to present a great deal of information in a short amount of time. Kudos! I am very grateful that you have stream-lined the process about starting seeds. I read the back of seed packs and don’t get a lot out of it. Always more questions then answers…. I just ordered seeds today and have been wondering about the heating mat now I will make sure all of my starts don’t have cold feet. I am putting all of your tips into play as I attempt to grow a garden. I just found you on Utube this evening so I really appreciate the information about container gardening as well. The information about the correct pot size is something I have struggled with so again Thank You for sharing excellent info for correct plant size. My yard is very shady except for a very few places so for the most part I will be container gardening. I am fairly new at this - my second real year -but really enjoy seeing the little plants grow. I live in NE TX so I do experience the extremes that Mother Nature throws at me here. Very hot in the summer and some winters very cold. ( this year so far is an exception. ) Thanks again for creating a site that covers real information on different aspects of gardening that is about gardening. Happy Gardening ~ M

Angela Judd

Monday 16th of January 2023

Thank you so much for your kind words and encouragement. Best of luck to you with your garden this season!


Wednesday 15th of June 2022

Thank you for the detail info! What do you think of soil blocks? I have trouble getting the seedling off the little plastic cells. Wondering what are the advantages and disadvantages of soil blocks?

Angela Judd

Tuesday 21st of June 2022

I've great things about soil blocks for starting seeds. The disadvantage could be it may be messier. I need to give it a try!

Margaret Vermeulen

Tuesday 8th of March 2022

Hi. The grow get you have linked on Amazon is not the ones in your picture of your shelving unit. I’m looking for 4’ long ones but the Amazon link is to a 2’ wide light. That won’t fit on the 18” shelf. Have you tried an LED instead of the T5? Thanks in advance for your help

Angela Judd

Sunday 13th of March 2022

Hi Margaret, The ones I have are these: and in the description they say they are about 13 inches and I just measured mine to be sure, they are about 13 inches wide. I'll check the links again and update them. I haven't used LED yet because I have these and don't want to pay to upgrade them.


Saturday 17th of July 2021

Hi Angela! What plants do you start indoors in the summer vs spring? For July, do we start indoors things that would normally be planted in August or September (according to your helpful lists)?

Angela Judd

Saturday 17th of July 2021

Here is a blog post that may be helpful: It lists when you would start seeds indoors to be ready to plant outside.


Friday 2nd of July 2021

Thanks to your post, I have a shelf full of happy seedlings! In anticipation of hardening them off for a monsoon planting, can you provide a little more detail about how it differs from hardening off for a spring planting? For example, soil temps will be much warmer, so should I keep them on the heat mat? It's hard to find advice online about monsoon planting, so any tips would be appreciated!!

Angela Judd

Monday 5th of July 2021

The tricky part with the new seedlings in the monsoon planting is the sunlight. To minimize this I would gradually expose them to morning sunlight and then provide shade if possible for the first week or two. Plant them in the evening so they have the night to settle in. As far as the heat mat, it can speed germination but usually indoor temps in the summer are adequate for growing seedlings indoors.