The manufacturer sometimes publishes charts detailing how long their fertilizers REALLY last. Suffice to say it's almost never as advertised. For Osmocote Plus under my conditions, for example, it's 4 months instead of the six claimed on the package. The six month number is for houseplants.

I operate under the rule of thumb that it's 2/3 what's claimed, but I have no idea it's a fair generalization. It depends on the temperature (higher = faster release) and watering habits (more water = faster release).

This post was edited by gosalsk on Wed, May 28, 14 at 9:12

I think gosalsk makes a good point. When using products like Osmocote or any other CRF I wouldn't count on the product lasting as long as the label indicates. I'm sure that in studies under ideal growing conditions in a laboratory Osmocote plus might well last up to 6 months, but in a backyard with fluctuating weather conditions I wouldn't count on it.

I think it was Ohiofem who indicated that she used Osmocote or Dynamite as a "starter charge" only, and never relied on CRFs alone for an entire season. Personally that idea makes sense to me.

When I make soil mixes I add 1 tablespoon of Osmocote Plus per gallon of soil. However, I also fertilize plants with a very weak MG 24-8-16 water-soluble fertilizer solution about once every 7 to 10 days, depending on the weather. The combination of the Osmocote and the MG fertilizer will ensure that my plants have everything they need.

Hope that helps.

TYG

I agree with both gosalk and yard guy. I'm guessing the Osmocote you are using is the three month formula that doesn't contain trace elements or magnesium and calcium. Any Controlled Release Fertilizer is released more rapidly than the label says in the higher heat and heavier watering conditions of outdoor containers. The two thirds estimate is probably a good guess. But instead of adding more Osmocote after two months, I start adding a soluble fertilizer with trace elements, magnesium and calcium about four weeks after planting and repeat that weekly through the rest of the season. Nutrients are leached rapidly when you have to water every couple days. And veggies like tomatoes and cucurbits are heavy feeders. The best advice I've gotten is to use soluble fertilizers "weekly weakly" meaning that if the directions say to give one tablespoon per gallon every two weeks, I give 1/2 tablespoon per gallon once a week. MiracleGro all purpose 24-8-16 has most of what you need.