mvftw wrote: ↑August 9th, 2020, 9:25 am
I have read from this forum that Mid-August is a good time for Slow Release Fertilizer.
I have 2 Lesco Fertilizer's:
32-0-10 +2% iron 21.6% slowly available urea nitrogen
25-0-6 +5% iron 11.25% slowly available urea nitrogen
My math would say that 32-0-10 is a better slow release.
But are they any good?
I have read that Milorganite is good to put down in mid-August, but I would rather use what i have, if it is Ok.
Also about how long is the shelf life of open bags of Fertilizer?
If 32% N has 22% slow N, then there's 78% (100-22) fast N. So 0.78*32 = 25-0-10 is the final number for fast release. (the potassium particles are not coated)
If 25% N has 11% slow N then there's 89% (100-11) fast N. So 0.89*25 = 22-0-6 is the final number for fast release.
The remainder is slow release, so the 32-0-10 has 7-0-0 slow release.
25-0-6 has 3-0-0 slow release.
Neither is good for August application as the nitrogen levels are too high at a time when the lawn wants a very light mid-afternoon snack of a small vegetable plate and perhaps a light fruit juice.
If those are your only options, skip the August application. It's not strictly necessary, just helpful. If you really want to put something down now, and can get to the store, pick up some Milorganite or any other grain-based feed.
These amounts of slow release are fine for the September feeding, however, so you can certainly use them at that point. And August is chugging along, so you can apply this around Labor Day. We can't say how long the slow release will last, so these would be once a season options. Don't use either one again within a...let's say four month period unless the bag specifically states that the nitrogen is released completely within a shorter period. The longest I've heard of significant nitrogen being released is about four months (Vigoro Super Green, which I use as my winterizer as I don't experience dormancy in winter).
The shelf life of open fertilizer is indefinite unless it gets wet. If you fold the bag over, or twist it shut, and it still flows, it should be good forever. Most fertilizers are urea-based, which will require some bacterial action in the soil to become active (it's minor and fast, and only takes a day or two). That won't happen even if they get wet, so the re-formed crystals can be broken apart if they get wet and dry out.
Other fertilizers are chemical and don't change form if they get wet. Again, just break them apart. However, these tend to turn to concrete and are more difficult to break apart.
In both cases, flowing them through the spreader will be a problem, so you can hand-spread very, very carefully, or use them in the garden, or discard them per bag instructions or your local ordinances. I usually use them in the gardens--they work fine, after all.