Starting Seeds Indoors that Thrive

By Hilary Rinaldi for Weekend Gardener

If you've starting seeds indoors in the past and they didn't do well, then let's start by getting rid of any preconceived ideas you may have formed:
  1. Starting vegetable seeds indoors is not impossible!

  2. Starting vegetable seeds indoors is not complicated!

  3. Starting vegetable seeds indoors is not only for hard-core gardeners!
Repeat the above to yourself - now - let's get started, because this is fun to do!
OK - So Why Bother?

There are several good reasons to start vegetable plants from seed indoors:
  • By starting vegetables indoors, you gain 4 to 6 weeks over crops started by seed in the ground.

  • If you live in an area where your summers heat up really fast, or you have a short growing season, this can mean the difference between getting a good crop of spring vegetables that like cooler temperatures, like peas, head lettuce, cabbage, broccoli and cauliflower, and not getting a good crop.

    The same is true if where you live has short summers. Heat-loving plants like tomatoes will get in the ground sooner, and you can harvest and enjoy them before the cool weather returns.

  • Your plants will have established themselves before the warmer weather hits and will better be able to withstand it.

  • You have many more varieties to choose from, because you are not limited to only what is available locally at your nursery as young plants. Try new tomatoes, onions or different kinds of pumpkins.

  • It's less expensive to grow your own plants than to buy them if you plan to have a full-sized garden.

  • Lastly, you have more control, because you don't have to wait for weeks until the soil outside is warm enough to germinate the seeds. When the soil outside hasn't had time to warm up, the seeds will just rot in the cool, damp garden soil.
Of course there are two reasons not start from seed and buy young plants at the garden center: 1 - It's easier, and 2 - It's less time-consuming. So it really depends on your situation - but let's assume you're going to be bold and start your plants indoors.


The great news is that you don't need expensive or fancy supplies to start your vegetable plants from seed indoors. Here's your supply list:
  • A south-facing or sunny window

  • A bag of potting mix that is fluffy and light, with a loose texture. You can even buy germinating mix made specfically for germination of seeds. Whatever you use, just make sure it has a good blend of soil, vermiculite or perlite, and sphagnum peat moss. Seeds don't like a heavy soil

  • Popsicle sticks

  • Waterproof pen or pencil

  • Clear plastic kitchen bags or clear plastic food wrap

  • A complete soluble fertilizer like a 15-15-15

  • Containers that are 2-3 inches (5.1-7.6 cm) wide, and 2-3 inches (5.1-7.6 cm) deep for planting - these can be: plastic cell trays (which I prefer), peat pots, Jiffy 7's, cut-off milk cartons, or Dixie cups. As long as the container has holes to drain, it's fine to use.
Important Note About Containers

One thing to keep in mind is that I don't follow the traditional routine of growing seedlings. In the past, you've been told to sow seeds in mass in one tray, and before they start to stretch, you transplant them into a larger container to finish growing; then they go out into the garden. Forget that! I don't do it, and you don't need to either.

What I do is sow the seed directly into the tray they will grow in until they're ready for the garden. By doing this, the plant's root ball stays intact, and you have healthier, sturdier plants. Plus - vining crops like melons and cucumbers that don't like to have their roots disturbed, can stay in one spot.

I like to use trays that have 20 - 40 individual cells, and that are fairly large, about 2 inches (5.1 cm) wide by 2-3 inches (5.1-7.6 cm) deep. I don't want to use a tray that has any more than 40 cells to it, because trays that have 60, 80, 120 or more cells, I feel, have too small a rooting area and the plants won't do as well.

By sowing your seeds this way, your seedlings won't crowd and stretch and you can practically start your entire garden in one tray. After all, you don't have to use one tray for each crop. If you are using a 40 count tray, you can have 5 tomato plants, 5 pepper plants, 5 onions, 5 annual flowers, etc. It's up to you, and since each one is in its own cell, you can water and feed individually to each plant's requirements.

Lastly, how many containers you will need will be determined by how much sunny space you have near your warm south-facing windows.
Getting Started

Your seedlings are going to be indoors for about 6-8 weeks, so approximately 2-3 months before your average date of final frost, is when to begin your seed indoors. My average final date of frost here is the end of March, so I will start sowing in February. If your average final date of frost is in April or May, you can start in February, or wait until the first of March.

Gardening isn't an exact science, so you will have to adjust the schedule to meet your area's weather. If you have to wait more than 8 weeks, because it's still too cold and your plants need to stay inside a bit longer, it's not a problem - you'll just have larger transplants with better developed roots.

Some ideas to try: herbs, annual flowers, onions, eggplants, celery, leeks, cantaloupes, watermelons, cucumbers, squashes, tomatoes, head lettuce, cabbage, broccoli, cauliflower, and peppers.

Fill your container of choice with the potting mix, but make sure it is premoistened. To premoisten, simply put the soil in a separate, large container and wet it through. You don't want it soggy, just moist.

Level with a piece of wood or a stick to form a flat surface.

Gently sow your seed into the mix. If you are using a 40 count cell tray as I do, then put only 1 or two seeds per cell. You can always thin the extra one out. If you are going to use a square peat pot, then sow only 3 or 4 plants per pot. Again, this is so you won't have to transplant them. If you sow too thickly you'll either have to thin them out or eventually transplant them into their own containers, which I don't like to do - but it's your choice.

Take a clean dry piece of cardboard, and press the seeds into the soil surface to make sure there is good, firm contact with the soil. This will help with germination.

Then sprinkle more soil on top, enough to cover the seeds. Rule of thumb is to plant seeds 4 times their diameter. For lettuce seeds that are tiny, that is about 1/4 of an inch (.64 cm). Just make sure to read the seed packet, it always gives a specific planting depth.
Mark your seedling flats, with your popsicle sticks and waterproof pen, noting the variety of vegetable, and date planted. This is good to do, especially if you are growing different varieties of a certain crop, because you can compare how they do. I do it mainly so I can remember what I planted when I move them out into the garden!

Place the planted container inside a plastic bag and tie it closed, or you can cover the tray with plastic wrap making sure the wrap stays off the soil surface. You won't need to water it again until the seedlings sprout.

Don't put the flat in a cool, drafty area, or one that's too warm, like on the window sill. We won't put them on the window sill UNTIL they have sprouted. If you have ever made bread, it's the same principle, you want a spot that is nice, and evenly warm. A good place is on top of your refrigerator, if you have room for it there.

Basically you want somewhere away from sunlight. Light that is too strong can dehydrate the flat, or it can cause too much moisture to be trapped under the plastic, which could rot the seeds.

As soon as the seeds sprout and have broken through the soil surface, remove the plastic bags or wrap.

Seedlings usually appear within 10 days to 2 weeks. If they don't, don't worry. They can sometimes take up to 3 weeks, from too much moisture or from being in too cold or drafty an area.

If for some reason, your seeds never appear, don't panic. Simply replant your container, improve the growing conditions for warmth and lack of light and try again. Gardening many times is an experiment, so don't worry about it.

Once the seeds have sprouted, they will need full sun, and that's when you move them to the sunny south-facing window. If you don't have one, here is where you may need to invest in lighting equipment, but most people have somewhere they can get full sunlight for their seedlings.

Remember to try to avoid large temperature fluctuations. So if the nights are still very cold and icy, pull the plants back from the windows so they don't get too cold. What you are after is keeping your seedlings in a nice, warm, even environment.

If you want to improve this process because you have a very drafty, cold house, you can buy heat tape or a heat mat. Heat tape has wires inside that you can plug in, and a heat mat is just that, a mat with wires. Put the tape or mat under the flats to keep them evenly and moderately warm. Normally, though, your warm south-facing window will do the trick.


Now is the time to start watering your new plants. At first, check daily, until you get the hang of how fast they dry out. Check the soil moisture by putting your fingertip in the soil. If it's not moist, water them. Some people water with room temperature water to reduce the chance of shocking the seedlings with cold water.

The two best ways to water your young plants to avoid washing them away are:
  1. From the bottom of the flat, just set the flat in a larger container, fill with water and allow the water to work its way up from the bottom. Once the surface of the soil is moist, you can take the flat out of the water tray.

  2. Use a spray bottle and mist them with fine spray.
3 to 4 weeks after sowing, when the plants are established, you can add some complete soluble fertilizer to the water. Fertilize only once or twice before they go into the garden. You don't want rapid growth right now, just a bit of food to keep them healthy.
Hardening Off

Your seedlings will be indoors for about 6-8 weeks. After that, during the next two weeks, you will want to start hardening them off by putting them outside for 2-3 hours a day in full sun and then bringing them back in. Then put them in sun for 2-3 hours and then in the shade for a few more hours and them bring them back in. By the second week you can leave them out all day and night provided it doesn't freeze.

Your goal for the last 2 weeks is the get the plants ready to be transplanted out into the garden without shocking them with a sudden move. They need to get used to being outside, and you don't want them to sunburn, windburn, or freeze.
Planting Out

Once it's time to get them into the garden, there are a few steps you want to take to make sure you don't give your new, young plants, transplant shock.
  • Try to transplant them in the late afternoon when the sun is low. This will keep them from drying out.
  • Make sure they are well watered before you plant.
  • Make sure the soil you are planting them into is moist.
  • Try to disturb the root ball as little as possible.
  • Water them in thoroughly, to make sure the soil has settled around the root ball.
  • Put down snail bait around the plants to make sure they don't get munched.
  • Keep them moist and well watered for the first 4-5 days to make sure they get established.
After that, you can treat them like regular plants and allow the soil to dry out slightly between waterings. Just try not to stress them by allowing them to get too dry and possibly wilt. Even soil moisture is best.
If you've never had success starting seeds indoors, now is the time to try again. As you can see, there is nothing hard or complicated about this. The supplies are minimal, and there is very little technique to it. It comes down to paying attention to a few details, and taking the time.

But after all, isn't that what gardening is? A great way to get away from everything, and everyone, and spend some time doing something fun.
With over 20 years professional gardening experience Hilary Rinaldi has a very real interest in making gardening fun, doable, and successful for everyone. She is a professional public speaker and educator in the horticulture industry.

Nicole Caldwell

Nicole Caldwell is a self-taught environmentalist, green-living savant and sustainability educator with more than a decade of professional writing experience. She is also the co-founder of Better Farm and president of betterArts. Nicole’s work has been featured in Mother Earth News, Reader’s Digest, Time Out New York, and many other publications. Her first book, Better: The Everyday Art of Sustainable Living, is due out this July through New Society Publishers.