This is the application of nutrients to the aerial parts of plants. It can be used for the treatment of all deficiencies for all types of growing plants. But you can only spray very small amounts of nutrients onto the leaves at a time, otherwise, leaf scorch or even defoliation may follow. If foliar spraying is to be successful there must be sufficient foliage to hold the applied nutrients, and plants cannot develop to a stage of growth when foliar treatment, would be effective unless the soil has been prepared properly before sowing or planting. So, although foliar feeding cannot take the place of the traditional method of applying fertilizers and manures to the soil, it is a useful supplement, for the following purposes:
- To give a quick boost to growth which has been checked by waterlogged soils, cold nights, biting winds and frosts.
- To provide nutrients quickly when roots are unable to absorb sufficient nutrients from the soil, due to an infertile soil, lack of soil moisture, low soil temperatures or a restricted, injured or diseased root system.
- To correct a deficiency of a particular nutrient, which is applied to the soil could be locked up in an unavailable form eg manganese.
- To supplement the usual soil fertilizer treatment during flower production when there is a big increase in nutrient uptake by the roots.
Foliar applications of potassium nitrate to roses have often produced more richly colored blooms and dark green glossy foliage.
Methods of application
Nutrients can be applied as dusts or sprays. Finely ground fertilizers may be dusted onto damp foliage but these are not as efficient as sprays because more of the fertilizer falls off the leaves and about twice as much fertilizer is required to give as good an effect as a spray.
So it is best to use sprays, especially when applying trace element fertilizers, which are required in very small amounts. The fertilizers listed in the table below are applied at the rate suggested, using an ordinary garden sprayer or a watering can with a fine rose.
Time of application
If deficiency symptoms have occurred at an early stage spraying should be done immediately there is enough leaf to spray, followed by a further application in 2-3 weeks since most of the first application will have fallen on bare ground.
Where a deficiency occurs every year it is best to apply the foliar spray before symptoms appear.
Always spray both upper and lower surfaces of the leaves, because absorption is greater through the under surfaces of the leaves.
Use a fine mist sprayer and add a leaf wetting agent (not a soap type) to the spray. This will help to reduce the risk of leaf scorch. Spray in late afternoon or on a dull day, since best results follow applications made under slow drying conditions.
Don’t spray if the weather is hot and sunny, or scorching will be severe. Avoid showery weather, or most of the nutrients will be washed off.
Always get an expert to diagnose a deficiency before you start treatment.