I like 3 or 4-inch square pots for seed starting, but you can use whatever you have on hand. Label them with the name of the seeds you’ll be planting in them and the date you planted.
I reuse pots year after year. Be sure to put them through the dishwasher to rid them of pathogens that may have survived from last year’s crops before filling them with soil mix.
Don’t use soil straight out of the backyard for starting seeds – ￼it’s too heavy and is likely to contain diseases that tiny seedlings can’t withstand. Purchase mix at your local garden center or follow a recipe from a good gardening book. I like Ideal Compost’s seed-starting mix. It’s organic, high quality and, for me, local (from Peterborough, NH).
Filling the Pots with Soil Mix
Pour some seed-starting mix into a large container and moisten it well before starting. Mix it with your hands to distribute the moisture evenly and to break up big clumps. It should be damp, but not too wet.
Scoop some soil mi￼x into your pot. Tap it gently on a table to settle the mix. Do not press it down with your hands – it will get too compacted.
Sprinkle a little more mix on top, if necessary, to bring the level up to about ¼ inch from the top of the pot.
Using Vermiculite for Seedlings that are Prone to Damping Off
There are some seeds, for example snapdragons, that are prone to fungal diseases that cause “damping off.” Damping off is pretty dramatic – thriving seedlings will suddenly keel over, usually in a wave of contagion that starts in one spot then spreads through the entire pot. Sometimes most of the damping off takes place beneath the soil before the seedlings emerge. Only a few plants will come up, and these will be stunted and not grow well.
If you suspect a pot of seedlings is damping off, isolate it immediately from your other seedlings and wash your hands well before touching any of your other plants. If it becomes clear over the course of a day or so that the disease is spreading to other seedlings in the affected pot, throw them all away. This disease spreads readily and it can easily get into all your plants if you aren’t ruthless about destroying sick seedlings.
That said, you can do a lot to prevent damping off from ever starting. For most seeds, providing good air circulation, using clean pots and reliable soil mix will be enough. But for those seeds, like snapdragons, that are susceptible to the disease, it is best to start the seeds on pure vermiculite.
Vermiculite is a mineral that has been heated to make it puffy and light. It holds water well but also leaves a lot of air around the roots of growing plants, which discourages damping off. It does not, however, have much nutrition in it, so seedlings growing in vermiculite for any length of time will need a little extra fertilizer.
Seeding the Pot
Open the seed pac￼ket and put a crease in the middle of one side of the envelope. Tip the packet over the pot and tap it with your finger so that seeds slide on to the soil. Move your hand around to distribute the seeds evenly and not too thickly.
Cover the seeds with a sprinkling of soil. Some seeds need light to germinate and should be pressed gently into the top of the soil but not covered (the seed packet should give you this information). Water the seeds lightly. I like to use a sports water bottle – it’s easy to control the amount of moisture.
Moisture Retention, Lighting and Air Circulation
￼Cover the seeds with a sheet of plastic wrap so they don’t dry out before they germinate.
Place the seeds either in a sunny window (south facing is best) or a few inches beneath fluorescent lights. I use shop lights hung on chains so that I can change the hanging height as the seedlings grow. Metro shelves work well for starting seedlings – they’re water proof and easy to hang lights on.
Some seeds, usually flowers (viola species are an example) actually require darkness to germinate. For these, cover the top of the pot with a piece of tinfoil. Open regularly to see if the seedlings need water or have germinated. Once they sprout, remove the tinfoil completely.
Air circulation is crucial for the health of your seedlings. If you’re growing them under lights, odds are the air will be quite still beneath them. Use a fan to stir things up. Don’t point it directly at the seedlings, but place it at an angle, just so that you can detect a little motion in the seedlings. The air circulation helps keep the stems sturdy and keeps harmful pathogens from growing.
Different plants like different temperatures (lettuce likes is cool, tomatoes like it warm), but I’ve found as long as the temperature around seedlings is between 60 and 70 degrees, most things will sprout. That said, some seeds are persnickety about temperature, and generally seed packages and catalogues will be specific about this if it really matters.
Thermostatically controlled heat mats can be purchased and are great for starting large numbers of peppers, tomatoes, eggplants and other heat-lovers. You may also simply look for a warm spot in your home, such as near a radiator, or place the seedlings on a heating pad set to low and insulated with a towel. Do monitor heating schemes carefully though, so the seedlings don’t dry out or overheat.
For things that like it cool, such as delphiniums and pansies, a not-too sunny windowsill (at least in my old house, which lacks thermal panes) will provide chilly enough temperatures. Sometimes, though, you’ll need to take chilling one step further.
Cold Moist Chilling or Stratification
Some seeds, especially perennial flower seeds, need to feel like they’ve been through winter before they will sprout. To germinate these seeds, we trick them with a technique called “cold-moist chilling” or “stratification.”
The seeds are mixed with a little barely moistened potting mix and placed into plastic bags labeled with the seed name, the current date, and the date the plants can be moved to warm conditions. I use plastic bags becasue they take up less room in the refrigerator, but feel free to seed into a pot if desired. Different plants require differing amounts of time in cold conditions; your seed package, catalogue or a good reference book, such as Eileen Powell’s The Gardener’s A-Z Guide to Growing Flowers from Seed to Bloom, will give you specifics.
When the Seedlings Sprout: Watering
As soon as you see the seedlings sprouting, remove the plastic wrap. Water them gently when they dry out, but don’t over-water or you may encourage damping off.
If you notice any of your seedlings damping off, throw them away immediately or the disease will spread through your other seedlings.
￼ Don’t fertilize your seedlings before potting them up – they don’t need the nutrition yet, and you could burn them.
Potting Up the Seedlings
The first pair of leaves that unfolds is called the “cotyledon.” The next set of leaves that emerge are considered the first “true leaves.” For large seedlings, such as zinnias, the cotyledon is big enough to hold on to when potting up. For smaller seedlings, such as petunias (which have tiny seeds), you will probably need to wait for the true leaves to emerge before the plant is large enough to pot up.
Prepare pots for your seedlings. You can use individual or multi-unit pots. Fill them evenly with damp potting mix (potting mix is coarser and has more nutrients than seed starting mix. You can also use seed starting mix, but you may need to fertilize the seedlings more often). Tap the pots so the soil mix settles, but do not pack it.Use a chop stick or pencil to make a hole for the roots in the center of each pot.
Gently tap the pot of seedlings against the edge of a counter to loosen. Turn the pot over into your hand. The seedlings should slide out in a clump.
￼Gently break apart the seedlings with your fingers. Try not to touch the delicate stems, but concentrate on separating the roots very carefully. You should be able to lift the seedlings one by one apart from each other. ￼Lift the seedling by one leaf. Do not touch the stem or you may crush it.
Choosing Seedlings to Pot Up
You will have more seedlings than you need. In general, choose the healthiest, largest seedlings to transplant.
However, if you are transplanting a mixture – for example, mixed colors of flowers – choose both small and large seedlings.
Some colors are naturally smaller than other colors and if you only choose the biggest plants, you may miss some colors altogether. White flowers, for example, are often more spindly as seedlings than brighter colors.
￼ Lower the seedling into the prepared hole, positioning the lower set of leaves just above
soil level (you can submerge as much of the stem as necessary). Gently nudge the soil in around the roots. Do not compact the soil. Gently water the seedlings to settle the roots.
￼ Place them back under the fluorescent lights or in the window, water them when they’re dry and feed them once a week with ¼ strength organic fertilizer.
Turn the seedlings regularly and move them around in the tray so they all receive the same amount of light and don’t lean.
A week or more before planting your seedlings into the garden, you will need to begin “hardening them off” – getting them used to direct sun and wind. Start by placing them outside in a shady, protected spot for a few hours.
Lengthen this time and the amount of sun they receive, until they stay out for 24 hours. Do bring them in if a frost is predicted or if the weather turns very windy or rainy, or they may be damaged.
Once they can stay out overnight, they’re ready to transplant. Try to transplant on an overcast and drizzly day with no wind if you can. Otherwise, late afternoon is a good time as the plants will have twelve hours of dark to adjust.
Make Sure the Soil is Not Too Wet
It’s essential that the soil not be wet when you plant, or it will turn hard as a rock when it dries out. A good rule of thumb is to pick up a handful of soil, squeeze it hard and then let it drop from your outstretched arm back to the ground. If the clod falls apart when it hits the earth, the soil is dry enough to plant. If, however, it remains in a muddy ball. it is essential that you allow the soil to dry out more before planting.
Protect the Soil from Compaction as You Work
Try not to walk where you will be planting, as this compact the soil. It helps to have a wide board to stand and kneel on when planting out; this disperses your weight and protects the soil.
Seedling Roots: Loosen them Gently (Usually)
Dig a hole a little larger than the root ball of your plant. Tap the bottom of the pot with your trowel do the plant slide out of the pot into your hand.
Unless you are transplanting a species that hates to have its roots touched (morning glories, for example) you should gently loosen the roots a bit. This is especially important if the transplant is potbound or if its roots are growing in circles. (Roots that are growing in circles will continue to grow in circles and can choke the plant.)
Placing the Seedling, Watering, Filling in the Hole
Lower the plant into the hole to just below the first leaves. Pour a little water into the hole to settle the roots (they should spread out in the hole and not be all scrunched up in one spot), then scoop the soil into the hole, tamping it down gently – don’t stomp it hard, or you’ll damage the soil structure. Water the soil around the base of the plant well before moving on.