Understanding a few basic principles about how fertilizers work and how they are marketed will help you sort through the clutter on the fertilizer shelves.
Why Fertilize
All plants require 17 nutrients for healthy growth. Hydrogen, oxygen and carbon are supplied by air and water, and the remaining 14 nutrients are found in the soil as minerals. In our container gardens, potting soil is usually made up of some combination of peat moss, compost and perlite or vermiculite, and likely contains minimal amounts of the necessary minerals. Plus, every time you water your containers, minerals are leached out as the water drains. So ensuring container plants have sufficient nutrients through application of an appropriate fertilizer becomes even more important.
Nitrogen, phosphorus and potassium are considered to be primary nutrients required for normal growth and these are the ones represented by the 3 numbers (like 5-5-5) on the fertilizer bag or box. There are 11 secondary and micronutrient or trace elements required including calcium, magnesium, copper, iron and zinc. All of these 14 nutrients must be present in the appropriate balance for a plant to grow properly.
As well as providing the basic nutrition for your plants, specific fertilizer formulations can correct plant problems if a nutrient deficiency is the cause. For example, yellowish-looking leaves can be a sign of nitrogen deficiency (but they can also signal under or over watering). Before just assuming that throwing some fertilizer on an ailing plant will improve it, do some research to determine what is really causing the problem – it could be lack of sufficient light, improper watering or pest or disease problems as easily as lack of nutrients.
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