If you plan to fertilize only twice during the season, one application should be after the grass has come out of its winter dormancy, for the Calgary area that’s usually mid May. The second application should be in early fall after the heat wave season has passed, late August to September.
Fertilizing the lawn in Calgary and Edmonton
Mid summer fertilizing is not recommended for the Calgary region; a spring application of time-released fertilizer should get your lawn through the summer months. Time-released fertilizers can take from two to six months so you’ll want to leave enough of an interval between applications to avoid burning the lawn but check the label on your product so you know how long each application is going to last.
Avoid an extremely high nitrogen fertilizer early in spring; nitrogen acts as a growing stimulant and could encourage weed and quack grasses rather than the grass you really want, so be patient, remove thatch and aerate – both will go a long way toward the health of your lawn. Thatch, the mat-like buildup of dead stems, should be removed to allow fertilizer to get into the soil rather than sitting above ground on the thatch layer and burning new leaves of grass. Aerating will get air circulating to the root level and also allow fertilizer to absorb easily into the soil.
Most fertilizers are sold as compete mixtures, which means they contain all three elements nitrogen (N), phosphorous (P) and potassium (K). Complete fertilizers tend to contain 3 – 4 times as much nitrogen as phosphorous and twice as much nitrogen as potassium. For most lawns, a ‘complete’ formula works well.
At gardenguides.com for the city of Edmonton, they recommend a slow release 4 – 1 – 2 to be applied once the temperature has warmed up to 20°C (usually mid May). Waiting until the soil is warm will allow the fertilizer to absorb and avoid running off due to the ground being frozen.
After fertilizer is applied, the lawn should be watered several times to allow it to soak into the soil. Avoid fertilizing during periods of drought; fertilizer sitting on the lawn could cause it to burn the grass so it’s better to skip an application and wait until after dry spells or restricted watering schedules.
About lawn fertilizer – reading the bag
Three elements of lawn fertilizer are:
Nitrogen (N) – will encourage growth and make it green! Nitrogen will promote sturdiness and strength in the roots and the shoots; it will also help the grass thicken up and fight off weeds.
Phosphorous (P) – will encourage the establishment of strong root growth and is often used to renew old lawns.
Potassium (K) – will enhance resistance to cold weather, disease, drought and general wear and tear. Potassium is generally increased for fertilizer mixes to be used as the before-winter application.
Fertilizer bags are labeled numerically for example: 30 – 10 – 10, where the first number indicates the percentage of nitrogen, the second is the percentage of phosphorous and the third is potassium. So, in a 100 lb. bag of 30 – 10 – 10 (the ratio being 3:1:1) 30 percent is nitrogen, 10 percent phosphorous and 10 percent potassium with the balance consisting of fillers, time release and easy-spread components.
Depending on the region you live in, your soil may already contain adequate phosphorous and potassium but the best way to know for sure is by doing a soil test to check the pH balance and existing nutrients in the soil. More about pH here.
Thanks for reading! I hope this simplifies the question of when to fertilize the lawn.
References: allaboutlawns.com author Dawn West and gardenguides.com author T.S. Owen.