Fertilization is a misunderstood task that is usually necessary as plants require certain elements to maintain their health and vigor. But how much fertilizer do they need? And when do they need it? Should the fertilizer be organic? Slow release or quick release?

The answers to these questions should not be guessed at, since the fertilizer could be wasted or, worse yet, damage to plants can occur.
The safest approach is to take a soil sample and get it analyzed using a kit - these can be purchased lots of places, but it’s worth your time to find local resources that can assist you before you head online or to the big chain stores. Check what’s available from your county or state parks, or even local universities or colleges. Here in Ohio, The Ohio State University has extension offices in each county that usually have such resources available.
The kits are easy to use, and the form that comes with the kit asks all the pertinent questions and is simple to complete. One of the questions asked will be what type of crop you are growing. Remember, soil tests were originally carried out by farmers. Lawns, flowers, trees (deciduous and evergreen), and fruit (soft berries or tree fruit) are all considered crops.
Soil usually contains sufficient nutrients for plants to grow vigorously, but there are situations where some necessary nutrients are depleted and need to be replenished. Such deficiencies usually occur among the micronutrients such as iron (Fe), copper (Cu) and zinc (Zn), manganese (Mn) and molybdenum (Mb). The presence of these nutrients in the soil is measured in parts per million. Plants do not consume them in great quantities, but they are essential for growth and the plants’ abilities to ward off or survive attacks by disease or insects.
Iron and manganese also play critical roles during photosynthesis. Deficiencies of either or both leads to plant chlorosis, in which the foliage appears yellow. The symptom is the same for both elements, so a tissue sample will be necessary to determine which is needed. Again, don’t guess! You could make things worse. Tissue samples are a little tricky to take and have analyzed, but the same local source you got your soil kit from is a good resource here as well.

Once your analysis has been completed, it is time to buy fertilizer. This can be confusing, however, as the analysis report will show amounts to be applied per acre (again, for farmers). Don’t despair, as the report will tell you which element(s) are deficient, and most fertilizer package information will tell you how much to apply in a residential setting.
What’s more confusing? The sheer number of fertilizers on the market! Let me take out some of the work for you.
What really needs feeding?
The usual suspects, broken down into groups:
The lawn
Summer flowers
Vegetables (root type and foliage or fruit type)
Fruit trees (peaches, cherries, apples, pears, etc.)
Soft fruit (strawberries, raspberries, etc.)
Trees (shade, ornamental, evergreen)
Shrubs, including roses
It looks like you will have to buy a new garden shed solely for fertilizer, but not so! Fertilizers recommended for one crop can also be fine to use on another crop. For instance, a fertilizer recommended for vegetables can usually also be used for summer flowers, and a fertilizer for shrubs can be used for soft fruit. Fruit trees have their own needs, as do deciduous and evergreen trees. Information on fertilizer packaging can be helpful here.
When do I feed?
In most cases, the fertilizer manufacturer lists feeding times on the packaging. If at all possible, purchase slow-release fertilizers. They provide a steady supply of nutrients for a period of three months, six months or nine months, depending on the fertilizer.
It is also important to know when to stop feeding - generally, by mid-August in my part of the country. Check your zone and cross reference the fertilizer instructions to know for sure. If you continue to feed after the recommended date, the plant will continue to develop new growth that may not have time to harden off before the cold of winter. This may cause dieback which, in some cases, results in the death of the plant.
Don’t skimp on fertilizing.
Most people feed flowers and veggies, but many do not feed trees and shrubs (except possibly roses). Most flowering shrubs would benefit from a feeding prior to flowering, and trees may also benefit. Again, don’t guess; take a soil sample, since there may be adequate nutrition already available. If you do feed your trees and shrubs, do so every two years.
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