What Is Horticultural Oil and Dormant Oil?
During the winter months, when plants and trees are dormant, we see the recommendation to spray dormant oil or horticultural oil to control insects on everything from fruit trees to lilacs. But what kind of oil is it that we are being told to spray? What Is The Difference Between Horticultural Oil and Dormant Oil? The main difference between many of the newer commercial horticultural oils is that they are more highly refined than past dormant oil products and they can be used year-round. Most commercially available horticultural oils (i.e. Sunspray, Scalecide, Volck) are refined from petroleum oil with the impurities filtered out. The final oil is then combined with an emulsifying agent that allows the oil to mix with water so they can be sprayed. A true dormant oil originally referred to heavier weight, less well-refined oils that were unsafe to use on plants after they broke dormancy because they would burn and kill plant foliage. These older dormant oils, however, have been replaced
