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Alison Arnold: Is Fertilizing (Always) Necessary?


This week, BPR gardening expert Alison Arnold explains when, how, and even whether to fertilize gardens.

Jeremy Loeb: Many gardeners are in the garden planting and getting ready for another growing season – is this a good time to put out fertilizer?

Alison Arnold: Gosh Jeremy It seems like an easy answer but there are a number of things that factor in like what type and overall health of the plants you’re growing, you’re history of fertilizing – some people always fertilize and others don't at all…

OK.. so you’ve talked about soil testing before… is that always a first step?

Soil Testing is important for new gardens and helps establish a baseline for pH and existing nutrient levels. And so once you add amendments and the basic requirements for proper pH, phosphorus and potassium level are met a small supplemental amount of nitrogen may be all that’s required.

Basically for established perennials, shrubs and trees all we want is a moderate rate of growth and good green color – so if you are pleased with the amount of growth, the color of the foliage and the overall health of the plant – you may only need to fertilize every 2-3 years.

What about annual flowers and vegetables that grow for only one season?

For annual flowers and vegetables where the growth is more immediate applying fertilizers at planting is time is helpful. For long season and rapidly growing vegetables, an additional application may be needed to keep them growing continuously through the season.

And Lawns? What about them – can they be fertilized now?

Cooperative Extension does not recommend fertilizing lawns in our area after mid March. We typically grow lawns with cool season fescue which slow down and can go dormant during the hot summer months and if they get an application of nitrogen fertilizer late like this they tend to develop diseases such as brown patch. So it’s not good for the grass and it’s pretty much a waste of time and effort.

I would imagine too much fertilizer is not always a good thing.

Sure. Over application can increase problems with both insects and diseases and can contribute to stream and river pollution from run off. It’s in the best interest of everybody and everything to really think through and assess whether fertilizer is really necessary..

For instance you may have plants that don't have good vigor or a healthy appearance.  Leaves for instance could be light green or yellow in color, they could be smaller than usual and fewer in numbers. And for shrubs and trees the annual growth of the twigs and stems can be shortened… these are signs of low fertility but they can indicate that the plant was not planted correctly or is experiencing stress from other things like drought or poorly drained soils.

So if fertilizer is needed what do you suggest?

Using cover crop and green manures, compost and other amendments to improve the soil environment is always foremost and important. Next I would suggest applying low analysis slow release fertilizers or amendments to provide the basic nutrients needed to maintain good healthy plant growth throughout the season.

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