Fertilizing your Lawn

How to Use Fertilizer:  Your Questions Answered

Complete fertilizers contain three essential nutrients: Nitrogen (N), Phosphorous (P) and Potassium (K). The number on the bag of fertilizer indicates the percentage of each of these vital plant nutrients contained in the bag. For example, Turf Food (20-5-10) contains by weight, 20 per cent nitrogen, 5 per cent phosphorous and 10 per cent potassium.  The remaining percentage is a carrier that is necessary for distribution and may contain additional trace elements. Many high quality lawn and garden fertilizers found in our garden centre will contain slow release properties for non-burning and long lasting results.

Fertilizer use


Q. How much fertilizer does my lawn need?

A. Turf grass fertilizers usually contain nitrogen, phosphorous and potassium in ratio of 4-1-2 (such as 20-5-10 or 16-4-8). There are many brands available but are all quite similar in this regard.

Your lawn needs a one-half kilogram of nitrogen for 100 square metres with each application. Check manufacturers recommendations on bag for actual coverage. Apply in early spring, late spring, summer and fall for a total of 2 kg. of nitrogen per 100 square metres in the growing season.

Q. How many bags of fertilizer will be needed?

A. The numbers on the bag are percentages, so a bag of 20-5-10 contains 20 per cent nitrogen. An18 kg. bag will therefore contain 3.6 kilograms of nitrogen (18 divided by five). In applying half a kilo per 100 square meters this 18 kg. bag will be sufficient to cover 720 square metres.

The manufacturer provides the coverage information on the packaging. Use this information as concentrations of micro and macronutrients can vary substantially.

Q. Do I water after applying fertilizer?

A. Yes, dry granular fertilizers need to be watered in to begin to dissolve them and take nutrients down to the roots.

Q. Is that the same with Weed and Feed and fertilizers with insecticides?

A. No. The active ingredient that kills the weed has to stick to the foliage. Apply Weed and Feed after a rain or on a wet morning grass or after watering. Fertilizers with insecticides are sometimes watered in and sometimes not. It depends on the insect being targeted. Read the instructions on the label for the appropriate method.

Q. How do I store fertilizers? Will they keep?

A. Unused fertilizers will not lose their effectiveness; but keep them in a cool dry place such as on a shelf or at least off the floor in the garage. Close any open bags. Moisture will do no actual harm but will make the product difficult to spread properly.

Q. How do I apply lawn fertilizer?

A. Use a cyclone type broadcast spreader for even distribution.

Q. Can I burn the grass if I use too much?

A. Yes you can. Most lawn fertilizers are very safe, with a proportion of their nitrogen in a slow-release form. Nevertheless, too much in one spot can burn the grass. It is a good practice to calculate the amount of fertilizer needed and apply only half that amount walking with the spreader in one direction and then apply the remaining half at right angles across the lawn (see illustration below).

Q. How much fertilizer do I apply to flower and vegetable beds?

A. A typical formulation for flowers and vegetables is 8-12-8 or similar. One kilogram of such a balanced formula per 10 square metres should be worked into the soil at planting time.

Q. Should I fertilize again through the summer?

A. Yes. Another application of one kilogram per 10 square metres of a balanced fertilizer should be applied close to each plant as a side dressing. Do this four to six weeks after planting and, in the case of tomatoes, after the first flower cluster has set fruit.

Q. What about established trees and shrubs?

A. Established plants do not need the high middle number, phosphorous, but it is acceptable to use the same formula.

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March 12, 2021 — Garrys Garden Gallery
Tags: fertilizer