Perennials can add pizazz, colour and variety to the landscape. Perennials are mostly herbaceous, so they die back to the ground in the winter and start up from their roots in the spring.  They add great value because they live for many years, provide a long blooming season, attract hummingbirds and butterflies, and give great cut flowers to enjoy indoors.  At Sunnyside our friendly and knowledgeable staff are here to help you make the right selections for your garden!  Perennials will add a new dimension to sunny, shady, wet, dry, or rocky areas; there is a perennial that will thrive in every location in your garden!  Proper selection will enable you to enjoy your perennials for many years and have fun creating colourful displays to enhance your landscape.

We carry a large variety of perennials from common to unique, including hot new varieties.  We start bringing in our perennials in late April and get fresh stock in on a weekly basis until August.  We have something to suit everyone’s needs no matter how green their thumb. 

Calgary’s climate presents unique challenges when trying to grow plants.  Chinooks can cause plants to start growing during warm spells, only to be knocked back once temperatures return within normal winter ranges.  The lack of humidity and dry soils add another obstacle to success with plants in our climate.  Don’t be discouraged; there are lots of different varieties that are spectacular performers for the Calgary area.  The work being done with plant breeding is amazing and each year we are inspired by new varieties that have improved hardiness, disease resistance, and ornamental attributes.


Perennials can be planted anytime from spring through the growing season up until three weeks before the ground freezes in late fall.  The best perennial selection will be found during the spring months, especially early spring blooming varieties.  An additional advantage to spring planting is plants will have time to establish before winter sets in.

Hardiness Zone

Hardiness zone is a geographically defined area in which specific plant life is capable of growing.  It encompasses climatic conditions such as a plants ability to withstand minimum temperatures.  Calgary is located in zone 4 within a Chinook area.  We experience a large variance of climatic conditions within the city, which change depending on where you are located.  You will notice different microclimates within your yard that allow you to grow plants that would otherwise be out of your zone.  It is recommended to use zones as a guideline when selecting plants but always remember that unusual weather patterns influence the success or failure of any given plant.  Zones 1, 2, 3 and 4 are ideal candidates for landscapes in Calgary.  Zone 5 perennials can be seen growing successfully in many different landscape situations; a little extra care may be required. 

Hardening Off

Hardening off is the gradual acclimatization of plants from indoor to outdoor temperatures.  Plants that have been growing inside – whether in a greenhouse or in your home – are tender and at risk of tissue damage from exposure to sudden temperature decreases.  It is important to harden off these plants to prevent any added stress or even drying out from cold temperatures. 

Hardening off involves moving plants outdoors during warm days and inside at night, and should be done for one week leading up to planting.  Plants can be left outside at night if there is no risk of frost; if there is a risk of frost cover your plants or bring them indoors.  Plants should be watered daily because pots dry out quickly and plants may not fully recover if they are allowed to dry out.  During extreme weather conditions such as heavy rain or hail, move the plants indoors to prevent damage.


Watering is a key component to success when planting.  Improper watering is the number one reason why plants fail in the landscape. On the prairies we generally don’t receive enough precipitation to maintain flower beds throughout the season.  Always remember: more water less frequently is better than less water more frequently.  When watering you want to allow the water to soak into the ground to encourage the development of deep roots, allowing the plant to better withstand stress.  Shallow watering encourages shallow rooting which can be detrimental to plants because when the surface of the soil dries out the roots do as well.  This causes unneeded stress to plants, especially to new transplants.  With the winds and temperature fluctuations we experience, water evaporates quickly from the surface of the soil so it is extremely important to water thoroughly to maintain soil moisture for plants.

Perennial beds should be watered heavily once a week.  During hot weather this should be increased to two times a week, maybe even three depending on the winds.  Newly planted perennials should be monitored and watered at least twice weekly until their root system becomes established.  The addition of a layer of mulch will help retain moisture, which is beneficial to all plants but especially to new plantings.

In the early fall allow the soil to dry slightly so plant growth slows down in preparation for winter.  Depending on temperatures, watering deeply every 2-3 weeks is ideal.  In the late fall it is extremely important to water everything thoroughly to increase winter survivability.  All plants, especially new plantings, need a good drink before the ground freezes; this prevents damage to roots from cold, dry soils which will prevent any unnecessary stress to plants.


Soil contains all the nutrients plants need to grow and thrive; unfortunately soils may not have nutrients in sufficient quantities to suit each plant’s needs.  It is advisable to add 2-3 inches (5-7.5cm) of organic matter on an annual basis which will help add nutrients to the soil.  Plants also benefit greatly from the regular application of fertilizer.  Regular fertilizing through the growing season will provide steady growth, maximum blooming and a longer plant life.

New plants:

It is strongly recommended to use a starter fertilizer at the time of planting for all new transplants.  Choose a fertilizer that is high in phosphorous, such as 10-52-10, will encourage the development of a strong root system which is necessary for healthy growth and production.  It will also help prevent transplant shock. You can continue to use this fertilizer throughout the first growing season.

Established plants:

There are a variety of fertilizer formulations available for established plants.  Regular applications throughout the growing season are recommended, following label directions.  Stop fertilizing at the end of July, late summer, as fall fertilizing may stimulate new growth at a time of year when plants should be hardening off and preparing for the winter.


Covering the ground around your plants with a layer of mulch will help conserve moisture, prevent erosion, slow weed growth, moderate temperature, prevent crusting of the soil surface, and protect against soil compaction. Organic mulches are ideal because they insulate the soil, reduce evaporation of water and, add nutrients to the soil as they break down.  You can use different products for mulching which include compost, manure, bark mulch, leaf litter, straw and other materials.  

Winter Protection

Most perennials will survive and thrive without any extra protection.  However if you have exposed areas in your garden it would be beneficial to add a layer of mulch to help protect against winter kill.  Winter kill is the death of plants by exposure to extreme weather. The freeze / thaw cycles we experience cause roots and the crowns of plants to dry out which can result in death.  It is very important to make sure plants are watered in in the fall, and exposed areas benefit greatly from a layer of mulch.  Pile snow on beds that are bare; this will help prevent soil from drying out and in turn prevent winter kill.

Dividing Perennials

Most perennials will eventually need to be divided; some perennials will require dividing after only a short time while others will be content for many years.  Dividing plants will rejuvenate them, maintain health and vigour, improve flower production, and increase the number of plants.  

In general the best time to divide perennials is in the spring when the foliage is between 5-10cm (2-4”) tall.    Spring flowering plants should be divided after they have finished flowering.  Peonies should only be divided in September.

How to divide:

  1. Water the plants to be divided.
  2. For larger plants cut back top growth by about two-thirds prior to dividing, this will reduce stress and encourage strong root formation.
  3. Early morning or evening is the best times to divide.  Avoid hot, sunny days because this will cause plants unnecessary stress.
  4. Dig up the entire clump, with as much soil as possible, and separate the young shoots from the woody center
  5. Discard the central woody section. Replant the new plants (divisions) as soon as possible at the same depth and water thoroughly.
  6. Different types of perennials:
    • For clumps that are easy to pull apart: gently pull pieces apart ensuring that each division has some stems and lots of roots.
    • For small perennials: use a sharp knife to cut clump into pieces. Ensure that each division has one growing point and lots of roots.
    • For large perennials: use a shovel to split up the clumps and ensure that each division has at least 3 stems and lots of roots.