Frequently Asked Questions

Osmocote labels contain information on the expected fertilizer longevity. For example, Osmocote® 18-6-12 has a listed longevity of 8-9 months at 70°F. Keep in mind that this is a reference point based on a constant soil temperature in a lab test. Since no plant actually experiences constant soil temperatures of 70°F and since higher soil temperatures accelerate the nutrient release from Osmocote®, the actual fertilizer longevity at a specific site can vary quite a bit.

The Scotts Company has conducted Osmocote® research for many years at a number of regional research centers. Controlled release fertilizer is tested under real-life field conditions and we have extensive data on the pattern and longevity of controlled release fertilizer release in these areas over many varying growing seasons. Based on this research, the current Osmocote® 18-6-12 bag label offers a general sliding longevity scale to help growers select the correct product for their climate.

Osmocote® 18-6-12 Classic

Osmocote® Plus and Osmocote® Classic products are 100% coated and designed for use in greenhouses with herbaceous crops. Scotts has several state-of-the-art research greenhouses in Marysville, OH and we have conducted many phytosafety trials with these products at higher than label rates to prove this.

Since higher temperatures accelerate nutrient release from controlled release fertilizers, it is very important that the grower select the correct product and rate for intended crops and growing conditions. The improved Osmocote® Classic line includes Lo-start, Standard and High-Start formulations that might be better suited for different crops or applications such as propagation. If you have never used controlled release fertilizers in the greenhouse, we recommend you start with a low rate of Osmocote® combined with a half rate of water-soluble fertilizer.

Since nutrient release starts soon after the fertilizer is applied, we recommend that growing media containing incorporated Osmocote® be stored in moderate conditions and is used up as soon as possible. If mix with controlled release fertilizer has been sitting around for an extended period of time, we recommend a thorough leach to reduce soluble salt levels.

Combination feed programs are an innovative fertilizer practice that many greenhouse operators have adopted in the past few years. This practice combines a low level of controlled release fertilizer (either incorporated in the soil mix or top-dressed) with a dilute water-soluble fertilizer program.

Growers can benefit a number of ways by using 2 types of fertilizers. The base controlled release fertilizer charge provides a constant nutrient diet to crops even in cool, dark spring weather when fertigation is impossible. The grower can vary the controlled release fertilizer rate providing more for heavy feeders and less for salt sensitive plants and thus maintain a single water-soluble concentration for all crops. Also depending on the Osmocote® product selected and when it applied, the controlled release fertilizer charge can provide significant post-production feeding at the garden center and at the consumer (where fertilizer practice are often deficient). Research has shown that this practice can result in higher quality crops with lower nutrient leaching.

The Scotts Company offers a wide range of fertilizers to fit different crop types, growing systems and climactic zones. Product sheets are listed on the www.scottsprohort.com web site. There are a number of criteria that one should consider when selecting a fertilizer program including: desired product longevity, N-P-K ratios, presence of micronutrients, economics. Some products are 100% coated and homogenous in nature, others are blends of controlled release fertilizers and other fertilizer technologies. Consult your local Scotts’ professional field expert force to help you fit the best nutritional program to your operation. They travel extensively in a given territory and observe what works best with area nurseries and crops. They will suggest candidate controlled release fertilizer products and rates for you to trial at your operation, which is the best way to fine-tune your controlled release fertilizer program.

The correct fertilizer concentration for a particular operation will depend on a number of factors including: feeding frequency, crop type, crop stage, growing media, pot size, leaching fraction and environmental conditions. Osmocote® labels have generic suggested application rates to help guide a grower, but the only way to determine an effective and optimal rate for your specific conditions if to conduct a rate trial. Consult your local Scotts’ expert for more details.

How much Osmocote® fertilizer should I use on flowerbeds or in the landscape?

Controlled release fertilizer applications to landscapes can provide a season-long feeding with a single application and help reduce nutrient runoff as well. Osmocote® 14-14-14, 18-6-12 and Osmocote® Plus 15-9-12 (8-9 month) are the formulations generally recommended for this purpose. Product can be top-dressed around the drip zone of the plant and either gently scratched into the soil surface or covered with mulch. Recommended rates: apply 10-15 lbs of Osmocote® 14-14-14 per 1000 sq. feet of area per application (or 1 to 1.5 teaspoons per sq. ft). For maintenance this application can be repeated every 3-4 months. Since Osmocote® 18-6-12 or Osmocote® Plus15-9-12 are longer term products, only 1 application per season is generally required, although there could be a reapplication after 6 months in warmer climates. Recommended rates are: 10-20 lbs per 1000 sq. feet of area per application (1-2 teaspoons per sq. ft).

If you have more specific questions, contact your nearest Scotts Territory Manager.