The Society receives many gardening questions. This page was created to share answers to some of the Frequently Asked Questions (FAQs). Get your Calgary gardening help here.
Growing Season Tips
When should I stop deadheading my perennials?
Deadheading perennials can extend the blooming time for some plants. However, deadheading should stop several weeks before the first killing frost. This will trigger the plant to start going into dormancy in preparation for winter. Allowing the plants to go to seed has some additional benefits. The seeds pods provide food for birds, winter interest in the garden, and will help trap snow and moisture for the garden.
Should I fertilize my lawn now?
Cool season grasses have two peak growing periods, early spring and early fall. Fertilizing during these growing periods provides nutrients when they are needed by the plants. Lawns should be fertilized with a high nitrogen fertilizer (for example 21-3-4) in May and July. Grass tends to go dormant in August and should not be fertilized at that time. A slow release fertilizer feeds the lawn over 6 to 8 weeks, which helps develop a healthier plant and root system better able to resist stressors. In late September, a winter fertilizer can be applied to promote deep root growth and nutrient storage for the winter. Stronger roots help get the lawn off to a good start the following spring.
Does leaving grass clippings on my lawn cause thatch?
Grass roots are the primary cause of thatch, not grass clippings. Thatch is made up of roots, stems, rhizomes and other plant materials. These materials contain large amounts of lignin (fibrous material) and decompose slowly. Grass clippings are about 80-85 per cent water with only small amounts of lignin, and break down rapidly.
To learn more about the practice of leaving clippings on the lawn, also know as grasscycling, read the information sheet from the City on the Society’s Resources page. The City also has lawn care information on their website calgary.ca.
Do I need to fertilize my containers?
Even plants growing in good quality soil need to be fertilized regularly to continue optimum growing, as the nutrients are used up by the plant and are leached out during watering. Choose a quality fertilizer that has micronutrients as well as nitrogen, phosphorus, and potassium. If you are concerned about burning your plants with fertilizer, choose an organic fertilizer as the nutrient concentrations are lower and you are unlikely to harm the plant if it is not diluted or applied properly.
Can I fertilize all my containers the same way?
Plants that bloom before producing fruit (tomatoes, peas, peppers) and root vegetables should have a fertilizer with a higher phosphorus (middle number e.g., 10-15-10) content applied. Non-flowering leaf plants, ornamental or edible, benefit from a fertilizer with a higher nitrogen content (first number). If root vegetables receive too much nitrogen, they will produce leafy growth at the expense of tuber growth.
Flowering plants in pots will stop producing flowers if they don’t have enough fertilizer. They need a higher phosphorus level to support blooming.
Liquid fertilizers get absorbed very quickly and do not last very long, so they should be applied every 2-3 weeks. Granular fertilizers release slower, but feed plants over a longer period of time. Be sure to water the container before applying the fertilizer. Follow the directions on the package for mixing the correct concentration of fertilizer and for the frequency of application. Some gardeners will fertilize more often, but with a solution mixed to a lower concentration.
How often should I water my vegetable garden?
Wind, temperature, and rain will affect the frequency of watering, but a vegetable garden generally needs about 2.5 cm (1 inch) of water per week. Water the garden when the soil is dry 2.5 cm below the surface during the growing season. If you are starting plants from seeds, watering may need to be done daily during the germination period and until the seedlings are established.
Watering is best done in the morning to ensure the plant foliage doesn’t remain damp over night. Extended periods of dampness can cause disease. However, watering in the evening is better than midday if you can’t fit in morning watering. This reduces evaporation loss.
Water deeply to encourage deep root growth. Ideally, water until the soil is damp 15 to 20 to cm (5 to 6 inches) below the surface.
Mulching around the plants reduces evaporation from the soil.
The Old Farmer’s Almanac has an interesting critical water period table for vegetables. It is usually when the flowers and fruit are forming. Visit to see their guide: https://www.almanac.com/when-water-your-vegetable-garden-watering-chart
When should I harvest rhubarb?
Rhubarb should not be harvested at all in the first year, and only lightly during the second year to ensure the plant becomes well established. Harvest stalks when they are at least 20 cm (8 inches) long and greater than 1.5 cm (3/4 inch) in diameter. To harvest, pull from the base of the stalk and twist slightly. Cutting rhubarb stalks leaves a short stub that can rot and damage the root. Leaves are toxic due to their high levels of oxalic acid, but they can be composted. Leave a minimum of 2 stalks per plant to ensure continued plant growth. Stalks from later season harvesting tend to be tougher than spring harvested stalks. Stop harvesting if the stalks become thin, or after mid-summer, so the plant can restore it’s energy for next year!
How can I attract beneficial insects to the garden?
Encourage biodiversity! Choose a variety of plants that bloom throughout the season. Plants of varying heights will attract different types of insects. Many beneficial insects prefer small, simple blooms.
How can I keep hanging baskets looking good all summer?
Soil in hanging baskets will dry out quickly, especially in windy conditions, so keep up with the watering – this is usually once per day and sometimes even more than that. Make sure you match plant selections with their site. Fertilize once every two weeks during the growing season with a water soluble fertilizer formulated for flowering plants. Deadhead spent blooms when necessary.
What can I grow underneath a large conifer?
Large conifers will compete with other plants growing beneath them for sunlight, water, and space. You need to be able to control these barriers to plant growth. The simplest, most workable solution is to set up planter boxes/containers and then plant shade-loving species in them. (Watering will have to be done on a regular basis as the plants might not receive sufficient rainfall). You are at least able to give the plants the soil and nutrition they require, without competition from the trees.
What are some herbaceous perennial selections for shady sites?
Hosta, bleeding heart (Lamprocapnos spectabilis), bugloss (Brunnera spp.), Ligularia, Astilbe, ferns, queen of the prairie (Filipendula rubra), among others. Visit the Perennial Plant of the Year page under Resources for more plant information. Society Members may visit the Society’s Plant Database under the Members Only section of the website.
How can I design my yard to conserve water?
Select water-wise native plants. Grow less lawn. Use mulch. Make sure your soil is healthy. Use compost. Install a rain barrel. Water only when needed. Sign up for a Design Your Yard workshop to learn more.
End of Season Tips
What plants can I overwinter?
Many tender perennials can be overwintered indoors. Plants that are geophytes (plants that propagate from bulbs, corms, tubers, or rhizomes) which we frequently all call bulbs, can be gently cleaned of soil and stored in a cool dark place over the winter. Usually, they are lifted (dug up) after a light frost, their leafy growth is removed, and stems trimmed to about 2 cm. After air drying for a few days, the can stored in dry potting medium in a cardboard box or unsealed bag. The challenge is to keep them dry (to prevent mould growth) but not so dry that they become desiccated. The stored plant should be checked once a month to watch for mould, provide a air circulation, and add a bit of water (if required). In the spring, they can be potted up, or when warm enough, planted outside.
A few of the common plants that can be stored this way are begonias, canna lilies , crocosmia, dahlias, and gladiolus.
How do I overwinter my geraniums?
Pelargoniums, commonly call geraniums, are related to our hardy cranesbill geraniums but are not hardy in Calgary. These plants can be brought inside and overwintered. They can be grown as a houseplant, have cuttings taken for starting new plants that are grown over the winter inside, or stored dry and dormant.
If you’re bringing your pelargonium in to be a houseplant, before the first frost trim the plant back about one third. Let the wound heal. Dig up the plant and clean the soil off the roots. Soak covered in water with a drop of dish or horticultural soap for about an hour or two to remove potential pests. Rinse off the plant, then pot in a clean container with fresh potting medium. Keep the plant isolated from other plants for two weeks. Ideally, the plant would be covered with a plastic bag with a few tiny holes (for air circulation). Check it regularly for pests. The plastic bag will contain the pests if they appear and should prevent their spread to other houseplants. If no pests are found, it can be moved to its winter growing location. Shoot tips may need to be pinched periodically during the winter to promote branching.
Take cuttings from plants growing outside. Cut a 10 cm length of stem from the tip. Remove flower buds. Let it dry overnight. The next day, brush a bit of soft tissue rooting hormone (#1) on the side of the stem. (Rooting hormone is not required, but it does help encourage root growth.) Plant the cutting in a pot with a soilless potting mix and water. Do not overwater or the cutting will rot. Pelargoniums prefer a drier environment.
Lift your pelargoniums before the first frost. Gently shake off excess soil. Stack them like cord wood in a cardboard box or hang them to dry. The plant should be stored in a cool dry dark place. They can survive this way due to their thick moist succulent-like stems. Periodically inspect the plants. Remove leaves that dry and fall off. You may need to soak the roots in water (1 to 2 hours each month of storage) if the stems lose any plumpness. The stems should remain thick and firm. If the stems shrivel, discard the plant. In late March, pot up the plant and water thoroughly. Place the potted plant in a sunny window to trigger growth. It may take a few weeks before you see new growth. Trim off any dead stems.
Start of Season Tips
What is hardening off?
Hardening off is the process of giving your seedlings or greenhouse grown plants time to transition from their controlled environments to the outdoors. Direct sunlight, strong winds, and fluctuating temperatures can stress plants. Plants need time to adjust to direct sunlight, so their leaves do not get scorched. Young plants also need time to adjust to greater temperature swings. The process thickens the cuticles on the leaves enabling them to preserve moisture.
Once outdoor temperatures are appropriate for your plants, harden them off over a period of several days to a week. Start on a warm day. Place the plants outside in full shade (in a sheltered location) and bring them back in for the night. If it is breezy, you may want to only leave them outside for an hour or two (do not try to harden off your plants on a windy day). Over the next couple of days, place them in dappled shade, increasing the amount of sun exposure each day. By the third night, they can be left outside overnight (only leave them outside if the low will be no colder than 5° C). The plants should be ready for planting in their final growing locations after day five.