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How to Start Heirloom Tomato and Pepper Seeds for Best Germination


Pepper Seedlings One Week After Germination

Pepper Seedlings One Week After Germination

Healthy garden-ready heirloom tomato seeds can be easily started at home, but success is more likely with some tried and true practices.  My first three years of starting heirloom tomatoes and peppers by seed were rather angst-ridden.  I was depending on selling hundreds of plants at market and I had never done anything like this before. I read, and watched, and worried, and called the seed companies and MN Extension Service ad-nauseum.

Fast forward 14 years and I am much more trusting of these  heirloom tomato seedlings to take care of themselves with just a little help from me.   Maybe all the fretting paid off in a cumulative knowledge of methods that offer seedlings optimum growing conditions.  In this post I’ll  pass on what I have learned over the years , in hopes that it will help you on your way to growing healthy plants in your garden or farm.  It’s a lot of information, so I’ve organized it into three sections:

I.      The Germination Process

II.     The Seedling Growth Stage

III.   The Potting Up and Hardening Off Stage

I’ll cover stages I and II today and Stage III in next week’s post.  Caveat:  I grow around five thousand heirloom tomato seeds each year now, but the principles of seed starting are the same.  Of course, you will have to modify your set-up if you are only starting a few seeds for a small garden or for pots (more on pot growing later).

I.  The Germination Process for Heirloom Tomato Seeds: 

Useful seed starting supplies

Useful seed starting supplies

1)  Timing:  It is important that your heirloom tomato plants be at the optimum stage of growth when you plant them outside.  This means stocky plants, with thick stems, about 5-9 inches tall, with good root growth (preferably in 4-inch pots so they are not root-bound).  You do not want tall thin plants with weak stems, because they will not transplant well.  Nor do you want huge plants in small pots that already have blossoms on them, because this means they have spent too much energy forming those blossoms, leaving them somewhat depleted and hence not able to yield as many tomatoes.

It takes about 6 weeks for a heirloom tomato seedling to reach this optimum growing stage (about 8 weeks for peppers).  So, wherever you live, determine when your weather is likely to be stable enough to plant in the ground and count 6 weeks back from that date.  In Central Minnesota, where I live, I start all of my tomatoes March 14th through March 16th, and I start the peppers about 2 weeks before that.  In mid-May, after they have been hardened off thoroughly, they are primed to get in the ground and start doing what they are destined to do….grow.

2)  “Soil” for seeding:  If you are a totally organic grower, you can make your own potting mix (but it is a bit involved).  I have tried several, but my favorite combination is as follows (you will need to scale down proportionally for smaller batches):

  • 5 gal. compost
  • 5 gal. peat
  • 3 – 5  gal. mix of vermiculite & perlite
  • 1/2 c. lime (don’t use this if your compost is horse manure as the beds are often limed)
  • 1/2 c. bonemeal
  • 1/2 c. bloodmeal
  • 1/2 c. greensand (or 1/4 c. sul-po-mag)

If you’re not worried about being totally organic, Miracle-Gro Moisture Control is a potting soil that gives consistently good results.  The main thing is, use a sterile potting mix, not garden soil.  Starting seeds in garden soil frequently leads to “damping off” of the seedlings, where they start to grow and then just keel over and collapse at the stem.  Garden soil carries disease-promoting fungi that is hard on young seedlings, not to mention the weed seeds prevalent in garden soil.

3)  Trays/Flats/Containers:  I use sturdy, reusable, 128-cell flats that have lasted a minimum of 5 years (and I am not gentle with my equipment).  Any container will work, including yogurt cups, peat pots, etc. as long as there are holes in the bottom.  One of the reasons I start my seeds in flats with small cells is to fit as many seedlings as possible under the grow lights, but an equally important reason for me is that the seeds will germinate faster in smaller cells.  The small amount of potting mix in each cell heats up more quickly, and there is not as much of a danger of over-watering.  It is worse for the container to be over-watered rather than under-watered (that damping off condition again).  *Note:  if you are using a grow light setup similar to mine, make sure your bottom tray that the cells sit in does not have holes in it or it will drain onto the grow lights below and short them out.

4)  Seeding Process:

Potting Mix Moisture Level

Potting Mix Moisture Level

  • Pour your potting mix into a large, shallow tub.  Add hot water in increments and mix well with your hands.  Take a handful of the mix and squeeze.  You want the potting mix to be damp enough to form a ball, but not so wet that you can wring water out of it with a gentle squeeze.
  • Fill the flat with the potting mix and then hold it slightly above the floor and let it drop to the ground to make sure the mix compacts a bit and gets into all the cells.  If the mix is too fluffy, the seed will not make good contact with the soil particles.  Refill any of the cells that are not full after dropping the flat.
  • Mark the heirloom tomato variety and the date on a small but sturdy tag (I use cut up venetian blinds I get at garage sales), and place the seeds on top of each cell individually.  Some people pour the seeds out carefully onto the cells, but it really doesn’t take that long to seed the cells individually (good time to listen to music or podcasts).
  • Now go back to the first cell and use the pencil with one hand to poke the seed slightly down into the mix and use your other hand to firmly cover the seed with a small bit of the soil.  If you are only starting a few seeds, and using individual containers, don’t poke the seed down too far into the soil.  It just needs to be slightly covered, about 1/4 inch.  The main thing is to make sure the seed has been firmly pressed into the soil.  Good contact with the soil is important to germination.
  • Cover loosely with plastic to keep moisture in and the seeds warm.  The clear tops that come with some of the flats are fine, but you don’t really need them.  The plastic is only on the seeds for a few days and then you are done with it.  Easier to fold up a piece of plastic and store it for next year than store the hard plastic covers.
Using 100-watt bulbs for Heat Source

Using 100-watt bulbs for Heat Source

4)  Heat Source: Warm soil is more important than warm air, which is why I use hot water when mixing up the soil.  My seed-starting shop is not heated, so I do use a small electric heater to keep the ambient air around 70 degrees during germination, but the main heat source for the soil is 100 watt bulbs placed under the trays.  A  heating pad placed under the flat would work also, but these lights were something I had on hand 14 years ago and they worked so well I never found the need to upgrade.  The 100-watt bulbs put out quite a bit of directed heat and the seeds all germinate within 3 days.  I do check the flats once a day and mist the cells with water if they look dry.  I will also turn the flats around if the germination is uneven.  Remember that germination time also depends on the seed variety and how old the seeds are.  The date on the seed package is a packaging date, not the date the seed viability was tested.  Buy seeds from a credible company and don’t keep them over for too many years if you want 100 percent germination.


Indoor/Outdoor Hose for Seedlings

Indoor/Outdoor Hose for Seedlings

5)  Watering/Misting:  Heirloom tomato seeds in the process of germinating  do not need a lot of water!  This is important because too much watering can lead to the damping off situation described above.  The plastic covering the flat should actually be enough to keep the cells moist until germination, but you should check the edges where it tends to dry out first.  I tend to keep the peppers on the dry side and the tomatoes a bit more moist.  When I do water them, it’s more of a misting with a gentle spray than a watering.  I use a small coiled hose attached to my shop sink.  The indoor hose pictured to the right is no longer available and I have switched to the  is a Water Right MCH-050-FG-6PKRS 50-Foot x 1/4-Inch Mini Coil Hose With Wand – Forest Green, which has a small nozzle, and it is perfect for misting the seeds at this stage and watering the seedlings with a larger stream of water later on.  I love this hose, but it does get clogged occasionally with the minerals in our water (we’re on well water) and needs to be cleaned regularly.

You’ve got seedlings!  Now the next stage:


II.     The Heirloom Tomato Growth Stage

End View of Light Set-Up

End View of Light Set-Up

Front View of Grow Lights Set-Up

Front View of Grow Lights Set-Up

1)  Grow Light Set-Up:  My husband set up a grow light system for me that involves five 4-tiered metal shelving units with 20 fluorescent light fixtures attached to each shelf (see example to the right).  Whether you have one light fixture or twenty, there are several key components to remember:

  • The distance between the light and the seedlings will change as they grow, so make sure the light can be easily adjusted up and down.  When the plants are very young, they will need to be fairly close to the light (about a 1-2 inch distance).  This is to ensure they do not get leggy and develop weak stems trying to reach for the light.  As they get bigger you can increase the distance so that the light source covers more area (around 4-6 inches distance).
  • Use two different types of fluorescent bulbs in the fixture; one warm bulb and one cool bulb.  You do not need to buy the expensive gro-light bulbs, the combination of warm and cool bulbs is really effective.
  • Keep the lights on the plants for 14-16 hours per day, but turn them off and let them rest at night.  A timer that you can plug the lights into is a must if you want to sleep peacefully.

2)  Day and Night Temperatures:  Once germinated, I tend to grow my heirloom tomato plants fairly cool to encourage slow steady growth that will give you sturdy, stocky plants.  I keep the daytime temperature around 65 degrees and the night temperature around 55 degrees.  At this stage it is important not to have wide fluctuations in temperature.

3) Watering:  Keep the soil moist, but not wet.  Heirloom tomato seedlings will need more water at this stage than when germinating, but it is still important to have a light hand with watering.  The plants are still very tender and should be watered gently.  I do love the The Rumford Gardener GA1001 40 Foot Indoor/Outdoor Garden Coil Hose with Spray Wand for this task because the small nozzle and stream of water allows you to easily water “around” the seedling rather than on top of  it, making sure you don’t break the stem.  The nozzle is also adjustable so you can use it for misting at the germination stage and watering at the growth stage.  It connects to the shop sink and the coil expands far enough that I can take it outside to water the plants when they are hardening off.

Thinning the Seedlings

Thinning the Seedlings

4) Thinning the seedlings:  Even if you have carefully hand-seeded, it is not uncommon to get 2-3 seeds germinate in one cell.  Make sure and snip off all but one (the straightest, strongest one) right at the soil line, so that they won’t compete for the same soil and water.  It’s difficult to snip a seedling sometimes, but it is worth it.  Do it.

5)  Air flow:  Some of the literature recommends running your hands across the seedlings periodically, tickling them, to make the plants stronger.  A fan works much better.  An overhead fan is ideal, but a floor fan or a table fan will work fine also.  Keep it blowing across the seedlings for most of the day and turn it off at night.  It really does wonders for the strength of the plants.  They must think they are outside in the gentle breeze of spring.  Just don’t let them experience the roiling  thunderstorms of spring at this stage of their growth.

6) Re-potting:  This is really important, and a big reason why your home-seeded heirloom tomato plants will be healthier than the heirloom tomato plants you often see for sale that have long since outgrown their small container.  When the seedlings are 3-4 inches tall and have their second pair of leaves, it is time to gently take them out of their cell and move to a larger pot.  I use a dull kitchen knife to slide down the side of a cell and pop the plug out without disturbing the roots.  I pot them up into a 4-inch pot filled with more of the potting mix that you used for germination.  If your seedlings have become leggy, plant them a little deeper in the pot, but do not cover the green leaves, as they are needed to provide energy.  Water the heirloom tomatoes well “before” you repot so the soil will stick to the roots and protect them from drying out.

7) Keep the re-potted plants out of bright sunlight for a few days so they can ease into the transition.  The next stage before planting in the ground is Hardening Off, which I will cover in next week’s post.

Comments are welcomed.  Share your tips and tricks…….this is what has worked for me, but I’m always learning.

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