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Annual Gardening

Starting Annuals from Seeds

Gardening in Southern Alberta can be quite a challenge. The shortness of our growing season is inadequate for most plants to be started from seed outdoors. You may wish to buy your annual flowers already started as this can be more convenient but also more expensive. The other option is to start your own seeds indoors. Starting seeds offers many choices in varieties, colours and growth habits. This will enable you to creatively plan your summer garden well in advance at a fraction of the cost when compared to buying bedding plants.

5 Things Seeds Need to Grow

  1. Soil - Need to ensure you have the proper growing medium for your plants. The mix should stay light and friable and for that reason you should never use garden soil. A soil-less media that contains sphagnum moss, vermiculite and perlite would be ideal. These mixtures do not contain much nutritional value but a seed contains all the food it will need to germinate.
  2. Temperature - many annuals are native to tropical and subtropical regions and therefore require warm soil temperatures to grow. For the most part seeds will germinate better if the soil temperature is constantly above 70°F, some varieties germinate better with temperatures between 80° and 85°F. That being said seed trays need to be in a place where they are constantly warm. It can be a slow process to germinate plants in a windowsill as the night temperatures and the morning temperatures can set things back. There are bottom heating seed propagation mats available to create a constantly warm environment conducive to seed germination. Another option is to place trays on top of your fridge.
  3. Moisture - Seeds need constant moisture to germinate. Never let the media dry out, it needs to be kept consistently moist but not wet. Water the media and mix it to distribute the moisture evenly prior to sowing. One of the best ways to maintain a moist environment it to cover the tray with a plastic dome or drape a piece of plastic wrap over top to keep the moisture in. Once the seeds start to sprout remove the cover so they can get some light and much needed air circulation. When watering seeds lift up plastic dome or plastic wrap then replace. Make sure to water with a very fine spray so that seeds don’t get washed away. Always try to use room temperature water and it is always advisable to let water sit for a day to allow the chlorine to dissipate.
  4. Light - most seeds do not need light to germinate, just warmth - moisture - darkness. Once seeds have sprouted and seedlings appear above the soil, light is necessary.
  5. Fertilizer - Not necessary for seeds as they contain all the food and energy they need to germinate. Young seedlings will need a weak fertilizer solution to grow and thrive.

Getting Started

Fill the containers almost to the brim with moistened soil. Smooth out and tamp down. As a preventative control for damping off (a common disease affecting seedlings) water media with a fungicide is recommended.

Sowing seeds - Seeds should be planted no deeper than the thickness of the seed. Carefully set seeds on the surface of the media and then sift extra soil on top to cover them. If the seeds are tiny simply press them into the surface or you can mix them with sand to ensure even distribution. Once seed’s have been sown cover the entire tray with a plastic dome or plastic wrap to maintain a moist environment.

When seeding into cell packs or individual containers sew 3 seeds per container, the extra seeds will act as insurance.

Place tray in a warm spot and make sure it medium stays consistently moist until you see seedlings starting to emerge.

Seedling Development


Light - without adequate light seedlings will end up wimpy, leggy, pale and weak.
  • if using a windowsill, make sure to rotate plants every couple of days so the seedlings grow straight up
  • use fluorescent lights. Use a fixture with adjustable height. Once germination has occurred lights should be practically on top of the seedlings - no more then 1" away. As the seedlings get taller adjust the height of the light fixture up. You want to have around 16 hours of light a day for best the growth and development of seedlings.

Moisture - once seedlings are growing start to ease of on the watering. Once the seedling is a couple inches tall, start to let the top half-inch of the soil actually dry out between waterings. Be careful as too much moisture encourages damping-off (root rot). Water less frequently and more deeply. Provide good air circulation.

Temperature - Seedling will grow well with air temperatures between 65° and 75°F. Bottom heat seems to help speed up developing plants.

Fertilizer - Once a second set of true leaves has emerged you can start fertilizing with Plant Prod’s Plant Starter Fertilizer 10-52-10 at ¼ strength once every ten days.

Growing On

Thinning-out - is an important step in the growing process Overcrowded seedlings develops into inferior plants so take time to remove weaker and excess seedlings.

Planting-up - Many individuals start seeds in a tray and then transplant them once they have developed true leaves. The reason for this is the best seedlings can be chosen from the lot and the remaining plants have more room to develop. When transplanting seedlings handle with care. Gently shake plants to achieve separation. Then set individual plants into a hole deep enough so that most of the stem is below the soil surface. This will help the plant develop a strong stem. Pack the soil gently around the plant and water lightly.

Damping-Off - if seedlings get attacked with damping-off throw out any infected seedlings. Then ensure seedlings that were not infected get plenty of ventilation and allow soil to dry between watering.

**Notes:
Most annuals grown from seed should be started 8-10 weeks before the last average frost.
Before moving seedlings grown indoors to their summer home, they must be hardened off. Refer to our “Hardening Off” brochure for more information.