The Gardener’s Corner

How to properly use fertilizer

Erik discusses the ins and outs of nitrogen, phosphate and potassium

Today I have decided to address the proper use of fertilizer.

When purchasing a bag of fertilizer, you will notice NPK and a number. This number indicates the percentages of nitrogen (N), phosphate (P) and potassium (K) in the bag, and the rest is filler to make the spreading easier.

To make any plant or fruit tree grow and produce a good yield, some fertilizer use is necessary.

When I operated the garden service in Victoria, one of the essential aspects for most of my customers’ wishes was a green lawn with no moss. To achieve this, I used fertilizer and lime after collecting a soil sample and testing it for pH.

The pH scale, I offered last week, indicate the condition of the soil between alkaline (nine) and acid (four). Most of the test results were well below six.

This soil condition, then, is favourable for moss to grow, but it also prevents the grassroots from obtaining nitrogen. This acidic soil condition has taken place because of the leaching out of lime, due to rainfall or watering.

Therefore, lime has to be applied annually. This issue has become the same in this area possibly because of the increase of rain.

To raise the pH level (acids), you will need to apply lime, but this can, for some vegetables, be a hindrance, so check the pH scale. Nitrogen also leaches out and needs to be applied annually; it needs warm soil to be obtainable for the root system, so don’t fertilize until the beginning of June. Potassium also needs to be applied annually.

I use a fertilizer 6-8-6 in most of my garden, also available at our feed store.

Nitrogen deficiency

Plant leaves are reduced, which results in pale yellow colour (chlorosis). Older leaves turn completely yellow.

Nitrogen deficiency can be prevented in the short term by using grass mowings as a mulch, or foliar feeding with manure and in the longer term by building up levels of organic matter in the soil.

Phosphate deficiency

Plants generally turn dark green ( leaves and stems) and appear stunted. In some cases, leaf tips will brown and die and appear weak and maturity is delayed. Prevention of phosphorus deficiency typically involves increasing the levels of phosphorus into the soil.

Planters introduce more phosphorus into the soil with bone meal, rock phosphate, manure, and phosphate-fertilizers.

Potassium deficiency

Potassium deficiency in plants, also known as potash deficiency, is a plant disorder that is most common on light, sandy soils, because potassium ions are highly soluble and will easily leach from soils without colloids.

Potassium deficiency is also common in chalky or peaty soils with a low clay content. Potassium is key in a plant’s ability to fight disease and begin fruiting. A plant lacking in potassium will show signs it in its leaves. Potassium-deficient plants will have brown or yellow edges along their leaves.

If you have questions or suggestions for topics, please email me:

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