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

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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. 

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10 Steps for How to Start Seeds Indoors

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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.) 

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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: 

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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!

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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. 

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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. 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. 

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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.

• Use a timer to have light on for 12-16 hours each day. 
• Use a fan to provide airflow for seedlings.

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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.

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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. 

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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.) 

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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. 

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