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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

Disclaimer: this post contains affiliate links. See my disclosure policy for more information.

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.

Perpetual Herb, Fruit & Vegetable Planting Calendar Zone 9b
  • PLANTING GUIDE: Each month lists vegetables, fruit & herbs to plant outside & seeds to start indoors.
  • HARVEST GUIDE: Photos show what may be ready to harvest that month.
  • Planting dates are for the low desert of Arizona (zone 9b).

How to Become a
Self-Sufficient Gardener

Learn other ways to become a self-sufficient gardener in this article.

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


Sunday 30th of July 2023

Hi Angela. I’m back... I’m using the same trays you recommend and a similar-sized fan. However, it looks like there is mold or something affecting my celebrity tomato seedlings. The pepper and black krim are just fine. The dome came off when half of the seedlings emerged.

Any treatment thoughts?

Angela Judd

Sunday 30th of July 2023

It's usually not harmful, but you can sprinkle a small layer of vermiculite on top of the soil and that helps with this.


Monday 10th of July 2023

Hi Angela. Our seedlings have popped - very cool as this is the first time we’ve done this.

Question: how long do you leave the fan on? All day or a portion or …?

Angela Judd

Thursday 13th of July 2023

Yay! Congrats! You can leave them on all the time. I usually leave them for the hours the lights are on and keep them on the same timer.


Tuesday 18th of April 2023

good morning Angela. I have several of your perpetual calendars that are like daily bibles to me. Love them. My question is this, when you list what to grow in each month, do you mean to actually plant seeds in the garden that month or transplants? I have been starting seeds indoors to plant in the garden on the month you stipulate, but wonder if I can put seeds in the ground on the months that you stipulate? Thank you!

Angela Judd

Tuesday 18th of April 2023

The dates listed are for planting outside. The newest version of the calendar also lists the seed starting dates for seed starting dates indoors.


Sunday 19th of March 2023

Your videos and directions are the BEST Angela! Thank you so much for taking the time to explain everything in such detail. I've got everything ready to go and am just waiting for the seeds I ordered to be delivered this week! Excited to start this!

Terri Steuben

Monday 27th of February 2023

I really appreciate the time and effort you put into details and explaining the steps. I feel like this should be so logical but I have had such a hard time with success on starting plants. Thank you so much! You're awesome!

Angela Judd

Tuesday 28th of February 2023

You're welcome!