With all the rain we have been getting here in the Southeast as of late, I haven't been able to feed my gardens, especially my Citrus, the normal way I usually do. A water soluable fertilizer is not a good idea to be applying when the plant is already water logged. Luckily, I have the technology to overcome this problem.....Foliar Feeding. Foliar feeding is a technique of feeding plants by applying liquid fertilizer directly to their leaves. I know, I am still applying water, just not near as much and not to the root system. Foliar feeding is not intended to completely replace soil applied fertilization of the macronutrients (nitrogen, potassium, and phosphorous). However, macronutrients can be foliarly applied in sufficient quantities to influence both fruit yield and quality. Foliar feeding is proven to be useful under prolonged spells of wet soil conditions, dry soil conditions, calcareous soil, cold weather, or any other condition that decreases the tree’s ability to take up nutrients when there is a demand. Foliar feeding is considered especially useful for introducing trace elements (micronutrients), or for "emergency" feeding of plants which are found to have a specific shortage. But in some cases, with tomatoes, for example, it is believed that foliar feeding during flower set causes a dramatic increase in fruit production. Ocean products like seaweed, kelp and fish are common components of foliar fertilizers because they're rich in micronutrients.
It all started when "Dr. H.B. Tukey, renowned plant researcher and head of the Michigan State University Department of Horticulture in the 1950s, working with research colleague S.H. Wittwer at MSU, first proved conclusively that foliar feeding of plant nutrients really works. Researching possible peaceful uses of atomic energy in agriculture, they used radioactive phosphorus and radiopotassium to spray plants, then measured with a Geiger counter the absorption, movement, and utilization of these and other nutrients within plants. They found plant nutrients moved at the rate of about one foot per hour to all parts of the plants.
Being a Citrus grower, I found this to be most interesting in the fight against Citrus Greening Disease. Several Florida citrus growers and production managers are using foliar nutritional sprays, mainly micronutrients, to slow down decline and maintain adequate fruit productivity of citrus greening-infected trees. Leaf application of nutrients is of significant importance when the root system is unable to keep up with crop demand or when the soil has a history of problems that inhibit normal growth. In other words,the reason this works with the Citrus Greening is because the disease effects the flow of nutrients from the roots to the leaves and fruit. The theory is, by feeding the plants directly through the leaves, the tree will maintain production a little longer.
As great as foliar feeding sounds, it does have some disadvantages. For one, it can burn the plants. Applications when the weather is warm (above 80 degrees) should be avoided. It is recommended that foliar feeding be done in morning or evening, since hot days cause the pores on some plants' leaves to close. Cloudy days would also be acceptable, however if rain is forecasted, best to wait. You don't want it to get washed off before the plant has a chance to taste it do you?
Just to re-emphasize, Foliar feeding is not a replacement for a healthy soil. Plants were not designed to take up nutrients through the leaves and fruit. Ideally, you want to get your soil tested, add lots of good compost, and generally take care of the soil your plants are in.
When I am giving my Citrus their occasional foliar spraying of Fish Emulsion, I tell them they are getting Pizza. They think they are just getting something else to eat, kind of like teenagers, they don't have to know it's good for them.