BUYER BEWARE: Over-the-Counter Fertilizers

Spring has arrived and soil temperatures in central Iowa are right at 40 degrees.  Lawns are still dormant currently but with some warmer weather coming we probably have 3-4 weeks before they start to grow.  Everyone is excited to get their lawn looking green, now is the best time to start mapping out your plan to achieve your lawn goals.

A couple of weeks ago I was doing some shopping at a large retailer.  They had their bags of pre-emergent and fertilizer on sale and I noticed them in many customers’ carts throughout the store.  It got me thinking about the analysis of it, so I grabbed a bag to take a closer look.  What was most surprising was the suggested use rate, of .8 pounds of nitrogen per 1,000 square feet.  That is A LOT of nitrogen, especially during a time when your lawn is going to have a flush of growth anyway.

Within our program, we won’t have applied that much all season until fall.  So, is it needed and how much of it is wasted in the atmosphere or into the groundwater?  The main source of nitrogen was urea, with some slow-release urea and ammonium sulfate.  The other concern is the effect of having that much nitrogen at one time in your soil’s biology.  Similar to phosphorus (depending on the source) applying that much nitrogen at once will interrupt your soil’s natural nitrogen cycle.  Bacteria needs to break down the nitrogen into a usable form for the plant.  Applying that much at once will hinder your soil’s biological activity.  If you haven’t fertilized your lawn in a long time, it will look great, but if you continue, you won’t see that same response because of the reduced soil biology.  Further, the slow-release nitrogen source, reacted with formaldehyde, inhibits microbes from breaking it down, compounding the effect on the soil’s biology.

What we have found to work very well is to apply small amounts of nutrients, more often.  Instead of just a lot of nitrogen and a little bit of potassium, we apply the full spectrum of macro and micronutrients and include all of the inputs for the plant to form complete proteins, thus reducing the need for bacterial inhibitors.  Combined with humic acid you get a longer carbon chain to slow the release which improves your soil structure as well.  We then add different biological inputs to increase diversity in the soil.  Now we see fewer ups and downs in growth and have addressed the soil structure, biology, and the grass’s nutritional needs.