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 steps of how to start seeds indoors, how to care for the seedlings, and what to do before planting them outside. It also covers the supplies you need to get started.
Disclaimer: this post contains affiliate links. See my disclosure policy for more information.
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.
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 January – February and again in June – July. 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. 4-6 Cell Seedling Pots for smaller transplants, or 3.5 inch pots for larger transplants (the ones I link to 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.
5. Seed Starting Mix – Sterile bagged seed starting medium. Do not use regular potting soil.
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.
- 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.
7. Heat Mat – Helps to maintain a consistent ideal temperature while starting seeds. Optimum germination temperature is when the soil is 70-80°F. 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.
8. Labels – Need to be small enough to fit inside the humidity dome when closed.
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”.
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).
12. Syringe – Helps remove excess water from trays.
13. Wire Shelving – Make sure the dimensions of the shelving will fit your seed trays.
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.
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!
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.
5. Plant seeds and add labels
- 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.
- Put domes on trays and place under lights on heat mats.
- Mist seeds lightly if they dry out; it may not be necessary to water until seeds sprout if soil is moist enough.
6. Remove domes, and provide light and airflow for growing 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 several sets of 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.)
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.
- 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 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.
Would you like the low-desert planting dates for vegetables, herbs, and flowers in a convenient calendar?
*PLANTING GUIDE: Each month has a planting guide (letter boards) for the vegetables, herbs, and flowers to plant in the low desert of Arizona.
*HARVEST GUIDE: Harvest guides are the harvest photos of what it is possible to harvest each month.
Angela, thank you so much. this is really detailed and i appreciate all of your efforts to put this together and help us get our seeds off to a good start!
Thank you Jackie. I appreciate the feedback. Best of luck as you start your seeds!
Thanks for the great detailed article and thanks for the links. Its good to be able to get what I need easily and help you out a tiny bit in return.
Tom
Thanks Tom. I am glad the information is helpful. Thanks for buying through the links, I appreciate it. Helps me to continue doing what I’m doing.
Thanks Angela. I took notes from your article and for the first time I feel like it might work. Normally I purchase plants but I’ve been wanting to start my garden this way.
Best of luck to you. It can be tricky for sure, but a skill worth developing!
Thank you for this!!! I have been searching for a thorough step-by-step guide to starting seeds indoors. I tried starting my seedlings a couple of weeks ago with no heat mat and no light source. My seeds germinated, but were SUPER “leggy.” I had to start over.
After reading this, I feel more confident this time.
Wonderful. Best of luck to you.
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!!
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.
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)?
Here is a blog post that may be helpful: https://growinginthegarden.com/when-to-start-seeds-indoors-a-seed-starting-guide-for-low-desert-vegetables/ It lists when you would start seeds indoors to be ready to plant outside.