To some, starting seeds indoors seems intimidating, but with some simple techniques and inexpensive start-up supplies, you can easily build a seed starting workstation and get your favorite varieties started indoors with minimal effort.  Why take the time, you ask, when you can more easily buy seedlings from a garden center or a farm-stand plant sale?

The benefit of starting your own seeds is that:

  • you can choose varieties that work well for your specific growing conditions,
  • you can choose from a much wider selection including rare or exotic varieties that are often not found at the traditional plant sales, and
  • you can start your seeds when the timing is exactly right for you.

I won’t be discussing the details here, but you can find more information about building you own seed starting workstation in an article I wrote last year.

Choosing Varieties

First, you will want to do a little crop-type and variety research to figure out which seeds need to be started indoors, as opposed to direct seeding in the garden.  Keep in mind that root crops and those with tap roots are often best direct seeded into the garden.  And while there are many crops that can easily be started indoors; timing, soil temps, and days to maturity play the biggest role in determining whether they actually need to be started inside.  Just because you can start a seed indoors does not mean that you have to or that you should. The following link is to a planting guide that will help you to determine what crops need to be started indoors, although some of this information varies regionally:

Calculating Start Dates

I usually calculate my start date by figuring out my intended harvest date and count backwards by using the days to maturity.  It is important to determine whether the days to maturity are from transplant or from seed.  High Mowing lists this information in the growing info section for each crop type.  Alternatively, if you have already determined your transplant date, you can use the above link to the planting guide to reference the number of weeks from seedling to transplant for each crop type to find out your seeding date.  Other details to keep in mind are the ideal air temperature and soil temperature requirements.  For instance, tomatoes require soil temperatures above 55 degrees F and frost free outdoor temps, therefore you want to be sure that you can achieve this by the time your seedlings will be ready to go in the ground.


It is important that you choose an appropriate size container for each particular crop type.  Some varieties, such as onions, are slow to develop their roots.  They need to be started in a small cell size like a 128 cell tray for 10-12 weeks before transplant.  Others, such as squash, are fast growing and require a 50 cell tray size for 4 weeks before transplant.  Tomatoes and peppers should be started in a channel tray and transplanted into a 50 cell tray or larger after they have developed their first true leaves.  You may need to transplant these again into 3 or 4” pots to keep them from getting root bound before they are ready for transplant.


First, you will want to prepare your soil by mixing with water until moist, but not soggy.  A good test is to hold a bit of soil in your hand and make a fist.  You will know when you have added the proper amount of water if you see a bit of moisture leak out between your fingers, but not enough to make a drip.  When you loosen your fist, the soil should keep its shape, but then easily crumble.  Fill your containers with a professional potting mix such as Vermont Compost Company’s Fort Vee, which is a general-purpose mix made up of manure compost, crushed granite, vermiculite, bone char, mined gypsum, sphagnum peat moss, kelp, and blood meal.

Some folks prefer the method of tightly packing the soil into the container, while others favor the method of packing soil into the cells more gently, followed by watering-in with a gentle shower which will pack the soil in, but without the risk of packing too tightly.  Add more soil and water-in again so that the soil sits just below the rim of the container or cell so as to allow a place for water to pool slightly during regular watering.  If the soil is packed all the way to the top, it is more likely to run off rather than penetrate.

Planting Techniques

Familiarize yourself with the cultural information on the package for each variety and crop type.  Most seed packets will provide you with the basic planting information and temperature requirements.  A general rule of thumb for seed depth is 2x the diameter of the seed.  Sometimes it is difficult with small seeded varieties to ensure that you are sowing one seed per cell.  After your seedlings emerge, you can thin to one seed per cell by pinching off the unwanted plants at the base of the stem.  For some crop types, such as onions, it may be your preferred choice to plant 2-3 seeds per cell and allow them to grow out this way.  While other crop types, such as cabbage, should always be thinned to one plant per cell.

After seeding, water lightly or you can use the mist setting on your hose, so as not to disturb the placement of your seed.  It is important to not allow the soil to dry out during germination, but equally important not to over water, remembering that the roots systems are yet to develope, therefore very little water will be taken up.  Over-watering during germination can also lead to fungal issues.  Propagation domes are clear plastic covers that can be placed over your tray during germination to hold in moisture and should be removed after your seedlings have emerged.  Water your plants regularly as the soil begins to dry, until you are ready to harden off.

Light Requirements

Full spectrum fluorescent lights, which can be found at any hardware store, are very valuable in that they provide a full light spectrum, while not producing too much heat.  They use very little electricity and are therefore fairly inexpensive to use.  Some folks ask if they can just put their seedlings in a sunny south facing window, but I advise against this because even the sunniest location will still likely not give adequate light.  Seedlings that do not receive at least 14 hours of direct light will become “leggy”, meaning that they will stretch and stretch to reach the light and therefore be very elongated and weak-stemmed.  Furthermore, the fluorescent lights should sit about an inch above your tray to give the most light possible.  As your seedlings emerge and grow, you can raise the lights link by link to keep them just above the tops of your plants; this will also help to keep your plants from becoming leggy.

Heat Requirements

Air temperature of 65 – 75 degrees F is sufficient for most crop types.  Some crop types however, such as tomatoes and peppers, require warm soil temperatures for germination and will benefit from bottom heat.  You can find seedling heat mats available at your local or online garden supply store.  Seedling heat mats are great because they are designed specifically for this purpose and provide the right amount of heat and are water resistant for your safety.  Additionally, a propagation dome will also help to hold in heat and can be removed after emergence.  Other crops, like lettuce require cool soil temps for germination, so it important to learn the needs of your varieties before you get started.

Ready for Transplant

Your plants are ready for transplant when their roots have filled out the cell, but before they have become root bound.  As long as the outdoor and soil temps meet the needs of your seedlings, you are ready to harden off your plants.  If your plants are becoming root bound before the ideal transplant conditions are available, then it will be necessary to transplant to a larger size container.  In this case, you will then have to wait until the roots have filled out their new container.  Resist the urge to transplant before the roots have filled out the cell because doing so too soon will disturb the root system and will set your plants back.

When you have determined that you are ready for transplant, you will want to harden off your plants before transferring them to their final destination.  Hardening off will help to prepare your seedlings for “the real world”.  To do so, you’ll want to slowly introduce your plants to the elements over the next couple of days.  On the first day of hardening, set your plants outside for just a few hours of direct sunlight and wind, and begin to reduce irrigation.  The next day, increase exposure to the elements to 4-6 hours.  Next, allow them to spend the night out.  Finally, you are ready to transplant!