Written by Kim Smerek

Maintaining a magnificent garden full of lush trees, flowers, foliage and fruit isn't as hard as it may seem! Just remember that plants need water, sunlight/shade, and nourishment.

So you've planted your garden, choosing the most beneficial positions for your plants, and you've been watering regularly. But how do you know that they have all the nutrients they need to develop strong roots, and lush foliage, flowers and fruit?  By feeding our plants, of course!  Fertilization is not done to keep plants alive, but to help them grow their best.  Fertilizers are like nutritional supplements. Many soils contain sufficient nutrients for the plants to absorb, but some soils do not, which is where fertilizers come in. 

By not fertilizing poor soils, nutrient deficiencies will affect plant growth. You can tell which nutrients your soil is lacking by the deficiency symptoms they display, which can range from yellow leaves (low nitrogen) to reduced flowering (low phosphorus) to weak stems (low potassium) to blossom-end rot (low calcium). A soil test is best to determine what your soil is lacking.

How do you know what your soil has and what it needs?

There are two soil tests you should do so that you know what you’re dealing with:  
1. The pH of your soil determines the availability of some nutrients, so it’s important to know if your soil needs a pH adjustment. pH test kits are available at Harper's. To increase or raise your pH, add lime. To decrease or lower pH, apply compost, manure or sulphur. The ideal pH for most garden plants is between 5.5 and 6.5.                                                                         

2. Soil composition tests show what your soil is made of. After this test you will know if your soil is sandy or clay based, and the best way to improve it. The ideal soil should be around: 40% Sand, 40% Silt, 20%Clay. Soil test results sometimes come with recommendations to add trace minerals to the soil if they are found to be deficient. The University of Guelph's Agriculture and Food Laboratory provides soil testing. (https://afl.uoguelph.ca/soil-testing-services).

What fertilizer do you use?  

Now you have your soil test results and you're ready! But what fertilizer do you apply? Here's a simple guide:  
Types of fertilizer:

Compost  and soil amendments - such as manure, wood chips, peat, grass clippings.

Organic- either certified 100% organic or including organic matter - like fish emulsion,   bone meal.

Powder, granular  and  liquid and water soluble fertilizers.

Slow-release fertilizers - one application works for months, so one application is generally all that is needed for a growing season.

Controlled release fertilizers - In general, the longevity of controlled release fertilizers are longer than slow release fertilizers.  

You'll notice three numbers on fertilizer packaging indicating the amount of Nitrogen (N), Phosphorus (P) and Potassium (K) (usually shown as N:P:K), in that fertilizer blend. These are the major chemical elements that directly impact plant growth and development.    

• Nitrogen helps plants produce nice green foliage.

• Phosphorus stimulates healthy root growth and development.

• Potassium, also known as potash, promotes bud and fruit development. As well, it helps plants fight off disease and keeps them vigorous. Plants deficient in potash may display stunted leaves and fruit and be extra sensitive to drought. 

Plants also require micro nutrients and trace elements to maintain optimal health. Here are just some:                                                                                     

• Calcium improves general plant vigour and promotes the growth of young roots and shoots.                                                                                                                                            
• Magnesium regulates the uptake of nutrients, aids seed formation, and contributes to the dark green colour of leaves, which is important for effective photosynthesis.                              
• Sulfur maintains that dark green colour, encouraging vigorous plant growth.   

When do you apply fertilizer? 

Generally speaking, the best time to fertilize landscape plants is around the time they begin to grow actively. The worst time to fertilize is at the end of their growing season. Different fertilizers are required at different stages of plants' lifecycles. Whether it's establishing a new tree or encouraging more flowers and fruit, there's a fertilizer to suit each stage of growth and development. Here's a simple guide:  

Young and newly planted trees  

What: Use a high nitrogen fertilizer to help develop strong growth. Additional applications of manure will also be of benefit.

When: Early Spring. If you are planting a nursery tree in the summer, one application at the time of planting and again the next spring when the tree has begun to grow.  

Dormant (deciduous) trees and shrubs  

What: Do not fertilize them while they are devoid of leaves!

When: Wait until the first signs of new leaves and flowers appear in Spring before fertilizing.  

Acid-lovers like hydrangeas, roses & evergreens  

What: Use a fertilizer like Supergreen Rose Food and Nutrite Tree & Evergreen Food which has been specifically designed to give acid-loving plants the nutrients they need to flourish.                                                                                                                                 When: Early spring just as their leaves begin to grow. For consistent blooms on your roses, you can feed them every 2 weeks with a water soluble rose food, such as Supergreen Rose Food

Native trees and shrubs  

What: Use a fertilizer designed for phosphorus sensitive plants.

Note: Native plants need fertilizer but they are accustomed to phosphorus-deficient soils and will react badly if high P fertilizers are used.  

Flowering plants  

What: To encourage flowering, most flowering plants benefit from a fertilizer high in phosphorus like Supergreen Perennial Food or Nutrite Flowering Plant Food. This is best applied as needed in Spring and Summer.

When: Use an all purpose controlled released fertilizer twice a year, and apply liquid feeds throughout spring and summer for maximum wow!  

Vegetable gardens 

What: Vegetable plants are rapid growers that deplete available nutrients fairly quickly. Feeding your vegetable garden something like Nutrite Tomato & Vegetable Fertilizer gives hungry plants a boost and ensures they remain healthy enough to produce a bountiful harvest.

When: Look for a vegetable and herb mix containing mycorrhizae, a beneficial fungi that increases the plants ability to draw nutrients from the soil. Vegetable plants also benefit from organic products such as fish emulsion or blood meal. However, while such products have great long-term benefits, they may not work quickly enough to save a malnourished plant. Heavy-feeders are plants that require a lot of mineral nutrients to thrive. Examples include tomatoes, cabbage, broccoli, sunflowers, and onions. Light-feeders are plants that either require very small amounts of mineral nutrients, or they themselves create nutrients. Examples include beans, peas, and lettuce.  


What: An All-purpose lawn fertilizer, usually high in Nitrogen. 

When: Ideally, most lawn feed needs to be applied when the soil is at least moist, so the perfect time is when you know rain is due. Fertilizing the lawn twice a year is generally sufficient – once in spring and once in autumn, though if you are already consistently mulch mowing, you could skip one or both. If you mow your grass a lot, or it spends a lot of time being played on by children, you may wish to fertilize it more frequently – up to a maximum of four times per year.  

• The label on the fertilizer will tell you the amount of fertilizer to apply and how often it should be used. Soluble fertilizers, for instance, are applied every two weeks during the growing season. Granular fertilizers are generally applied about every six to eight weeks. Slow-release fertilizers work for months, so one application is generally all that is needed for a growing season.  

• Apply plant food carefully as too much fertilizer is always worse than too little.   Keep fertilizer off the foliage and always water well immediately after feeding.

• To boost specific mineral nutrients, here are some organic options:

For Nitrogen: Fish emulsion, liquid fish fertilizer, blood meal.                                                    
For Phosphorus: Rock phosphate, bone meal.                                                                             
For Potassium: dried kelp meal, muriate of potash or sulfate of potash, ash from a wood fire, plant winter rye as a cover crop.