A summary of advice excerpted from Master Gardener emails and chat groups.
Start Dates
Check seed packets for information on start dates, lighting requirements, sowing depth, and optimal germination and growing temperatures.
Internet sites and books will help with this also.
Nursery Beds
You may wish to have a “nursery” bed outdoors.
Mark your calendar with your LFD (last frost date) and count back number of weeks specified) Record which seeds need starting on which weeks.
Containers
Larger seeds may be started in pots, smaller may be planted in flats with drainage holes.”
Anything can become a container, as long as it has drainage holes and is deep enough.
Plastic salad containers come with lids and work well!
All containers must be sterile. Use bleach and water to sterilize everything used for the seedlings.
Tomatoes from seed need to be started at 6 to 8 weeks before your last frost date; it is not beneficial any earlier.
The Dirt
Use pre-mixed sterile soilless mixture. (Not with fertilizer)
Garden soil will harden quickly, and to avoid damping off do not use compost.
Wet the mixture first in a bucket with lukewarm water, making it as damp as a wrung-out sponge.
Cold Stratification
Some perennial, shrub or tree seeds require a cold period for germination.
Need to ‘scarify’ seeds?
Some perennial seeds have a very hard seed coat which needs a process called “scarification.“
Put some sandpaper on a block of wood, the seeds in a small foil plate, and run the sandpaper over the seeds for a couple of minutes.
“I just put them between two sheets of medium grit sandpaper and sand them — gently.”
Identification
Sprouted seedlings will tend to look alike. Use plant identification markers to label each variety of seed!
“I use pencil for long lasting labels.”
Germination
Most annual seeds don’t require any special treatment for germination.
Some seeds need light for germination and should be sown on the surface. Others need to be covered. A light sprinkling of soilless mix or vermiculite is ideal for covering the seeds.
The three requirements for most seeds to germinate are moisture, heat and light.
Cover containers with a clear plastic dome, wrap, bag or glass to conserve moisture and keep up humidity.
Remove covers and heat mats when germination begins to prevent disease and spindly weak plants.
Remove covers for an hour or two if moisture is excessive.
Some seeds need warmth to sprout. Invest in a heat mat and place it under the seed tray. Keep it dry and on for at least 8 hours a day.
Drape flats with newspapers, cardboard or foil over the plastic cover for those that require darkness and place in a closet or other dark spot.
Only have a few valuable seeds? Germination rate slow or low?
Put down a layer of paper towel (shop towels work well because they are thicker), cut to the size of (any) container bottom. Add seeds on top. Place another layer of paper towel on top of the seeds and wet the towels. Place container in a warm place and wait. Check every few days. As soon as roots start to grow, gently pick them up and plant them.
“I find this technique reduces the number of pots I have sitting around that will never germinate.”
Put some seeds, a bit of soil (use only a small amount of soil so that you can see the sprouting roots) and water in a baggy and seal. If the seed is larger like tomato seeds you need just enough to coat the seed and keep them moist. If the seed is small like poppy seed, you don’t need any soil. The water will just coat the seed. You want the seeds moist, but not swimming in water or they may rot. This process is great for seed that needs a cold treatment; just refrigerate. (Good for peonies for warm/cold/warm treatment.)
To plant smaller seed, just wash the contents of the baggy into one pot.
Germination success weakens with age of seeds.
Newly sown seed flats should not be in direct sunlight, which is often too hot or drying.
Bottom heat will speed germination considerably but is not necessary.
One thing you can do instead of using a heat mat is to attach your fluorescent lamps on the underside of metal shelves so the lamp below heats the shelf above, or start your seeds on top of your fridge.
SEEDLING CARE
Dampening off
Warm, wet conditions make seedlings prone to fungal attacks called “damping off” which can kill seeds or seedlings before or after they germinate.
“As seedlings emerge sprinkle cinnamon powder around them, (which acts as a natural fungicide), to guard against damping off. Since using it I have never lost a plant in the hundreds I have started.”
Hydrogen peroxide and water about 1 tbsp to 1 cup, or chamomile tea both work as anti fungals. Apply with a sprayer sparingly.
Use garden sulfur sparingly.
Have good air circulation. (a small fan gently moving the air)
Avoid over watering.
Watering
Bottom watering is recommended.
Capillary matting is a highly absorbent fabric that enables bottom watering efficiently. It must be kept clean and can be cleaned with detergent and rinsed thoroughly.
Use water that’s at room temperature and let it stand overnight to allow chlorine to escape. DO NOT OVERWATER!
Thinning
Seedlings scattered on the surface of a flat will probably need thinning to one plant every 1 ½ – 2” before they are large enough to transplant. The safest way is to snip off unwanted ones at soil level leaving all roots undisturbed. Prick out seedlings using a small stick, pencil, knife, etc and transplant when the time comes to do so.
Fertilizer
When seedlings have two sets of true leaves (the first leaves are called cotyledons—or seed leaves), start feeding once a week.
“I recommend 1/4 teaspoon of 20-20-20 per 4 litres of room-temperature water.”
Commercial formulations are available, just follow directions.
Growth will be more even and burning of young plants will be avoided.
As the seedlings mature, you can gradually increase the strength of the dosage to 1/2 the strength of the recommended amount on the label. Your seedlings should be a healthy, strong green color.
Lighting
Plants grown on a windowsill will probably be leggy because the amount of light in March is not really enough for most plants.
All fluorescents produce a fraction of the light that plants get from the sun and they all produce less light than plants really want for growing.
“Mixing a warm and a cool bulb in the same fixture is a good idea to give more blue light. I would definitely use this for growing indoor plants. For seedlings, it is less important to use two types and 2 warm bulbs will give you more intensity of light.”
These bulbs can be found at your local hardware store.
Plug lights into an automatic timer set for 16 hours on, eight hours off.
The lights should be as close to the plants as possible- just 3 cm above works best. As the plants grow raise the lights.
Transplanting
When the seedlings have a true set of leaves (not the seed leaves, cotyledons, which will look different) they are ready for transplanting into their own pot. Hold the seedling by the seed leaves as these are no longer necessary for the plant.
Use a richer soil based medium (potting soil) as the seedlings require more nutrients to grow.
Keep the temperature cool as they will grow too quickly and become spindly. As the plants become larger and have more leaves on them you can replant them in a larger container.
Hardening off
A couple of weeks before planting make sure you take the seedlings outside in a sheltered place to begin to harden them off. (Exposing them to the outside)
Keep pots out of the wind and harsh hot sun.
Start with a half an hour the first day and gradually increase for about a week.
The plants will then be ready for transplanting in the garden as long as nighttime temperatures are consistently above 50F or 10C.
“I highly recommend keeping a garden journal that includes the variety of seeds, the date and location of planting, the garden’s last frost date from year to year and growing notes. Your garden may have ‘micro-climates.’”
Storing seeds
For storage, the key is to find a cool, dry, dark place. Paper bags or envelopes make better holders for seeds than do plastic bags because the paper “breathes.” If there is any moisture at all on the seeds, it won’t evaporate from inside a plastic bag and can cause mould.
Questions?
For free advice ask Master Gardeners, phone 519-824-4120 ext. 56714 or email to mgguelph@hotmail.com
By Katherine Granger, Guelph-Wellington Master Gardeners.