Healthy soil has a variety of nutrients in it to help your plants grow strong enough to defend themselves from most (but not all!) pests and diseases. Soilless mixes, like you'd use in a pot or a container, do not contain any soil at all. They are typically a mix of peat moss, perlite, and vermiculite and have almost zero nutrient value. They are essentially organic sponges. Unless you add fertilizer, in the form of compost or other types of fertilizer, your plants will not produce well and will be prone to many pests and disease issues.
When and When Not to Fertilize
Lawns should be fertilized on approximately May 15 with 2 to 2.5 kg of 27-14-0 or 26-13-0 per 100 m2. Six weeks later apply 2.0 kg of 34-0-0 per 100 m2. Six weeks later apply 2 kg of 34-0-0 per 100 m2.
Trees and shrubs generally do quite well on Saskatchewan soils without the addition of chemical fertilizers. Most problems associated with trees and shrubs are due to lack of proper watering or insect problems and are seldom attributed to lack of nutrition. Excess fertility in the soil promotes excess succulent foliage which is more susceptible to winter injury.
Vegetable and flower beds usually require 11-48-0 or 16-20- 0 applied in spring at the rate of 2 lb per 100 m2.
Fall fertilizing of trees, shrubs and lawns is not recommended in Saskatchewan. In warmer parts of the country, it may be a common practice, but not in the cold prairies. Because fertilizers encourage growth, fall fertilizing may stimulate plants to continue growing when they should be "hardening off" in preparation for winter. Plants that have not hardened off properly will likely suffer from some sort of winter injury.
Never put granular fertilizer or fresh manure in the planting hole. The chemical salts within the fertilizer may desiccate or "burn" plant roots.
How to Apply Commercial Fertilizer
On lawns, to apply granular fertilizer,
In vegetable gardens and annual flower beds, fertilizer may be applied in several ways: (1) fertilizer can be broadcast and thoroughly incorporated into the upper 7 - 8 cm (3 inches) of soil in spring prior to planting; (2) or it can be side-banded that is, incorporated along the sides of each row and about 5 cm deep (2 inches). This involves more work but is more efficient because less fertilizer is used; or (3) fertilizer can be placed around each plant, 5 cm away and 5 cm deep (2 inches). This last method is even more "labor intensive" than side-banding but it is also more efficient, in that all of the fertilizer is placed where it can be used by the plants. In perennial borders or other permanent plantings, fertilizer should be incorporated around each plant, 5 cm (2 inches) deep and 5 cm (2 inches) beyond the roots.
Seasonal Growth Patterns
In early spring, buds which have been dormant over winter begin to grow in response to warming temperatures and lengthening days. With most trees and shrubs, growth occurs rapidly and continues only until about early or mid-July. At this time growth ceases, and the plants begin to harden off and prepare for the winter. You can check this by examining the tree or shrub. If the leaves at the outer tip are the same size as the leaves lower down on the branch, then you know that growth has ceased. Look carefully and you should also see a bud at the base of each leaf, and a terminal bud at the very tip of the branch.
Some plants, such as raspberries and elderberries, tend not to cease growth in July, but continue growing slowly, sometimes right up to killing frost. When this occurs, the plant has not hardened off properly and, as a result, tip die-back occurs. Any plant that continues growing until late in the fall is susceptible to this form of winter-kill. When fertilizing trees and shrubs, it is best to apply the fertilizer in early spring when the plant is actively growing. By early July, fertilizing should cease.
Lawns are an exception to this; ideally, urban lawns should be fertilized three times a year (May 15, July 1, August 15). Lawns should not be fertilized later than mid-August, for this will encourage growth too late in the fall. Because lawns are low to the ground and usually have a good snow cover, they are more protected from the winter environment and therefore less susceptible to winter-kill than trees and shrubs.