Buying fertilizer is a bit like buying disposable diapers: many people stand in front of the display in wonderment about where to start. There are so many!

Here is the Mark Cullen Primer on fertilizers:


The 3 number analysis

It is required by law that all fertilizer products in Canada display prominently the % of each: nitrogen, phosphorous and potash (always in that order).

These elements are displayed on every fertilizer package as they are the three most ‘in demand’ elements used by plants in their manufacture of food. Note that fertilizers are not ‘food’: they provide nutrients that assist a plant in its manufacturing of food through the miracle of photosynthesis. ‘nough said. You don’t need a science degree to understand this, just the basics.


What do they do?

  • Nitrogen: generally is used by the plant to produce chlorophyll, which is the stuff that makes leaves grow and green.
  • Phosphorous: encourages root development and flowering/fruiting on many plants.
  • Potash: is an enabler for both the nitrogen and phosphorous and ‘build strong bodies’ by strengthening the ‘bones’ of a plant.

When do I use fertilizer?

Some plants do not demand a lot of nutrients from the soil and as a result they do not benefit greatly from the addition of fertilizer. I use a lot of compost and composted cattle / steer manure in my garden and as a result I minimize the need for fertilizers.

However, tomatoes and roses are two common garden plants that have a high demand for nutrients and benefit from the addition of fertilizer.

I use ‘Once and Done’ on my roses as it only is applied once a season (now is the perfect time!)

For my tomatoes I use an organic granular product- from Green Earth. It is 100 per cent natural.

Lawn fertilizer is another story. I use Iron Plus early in the season (a Golfgreen product) and again in late spring/early summer. I then apply a late fall winterizer fertilizer to strengthen the lawn for the coming winter.