Foliar fertilizer A foliar fertilizer is one that is applied to the surface of the plant Foliar uptake is important to aquatic plants and when nutrients are sprayed on foliage in horticulture and agriculture◼ A foliar fertilizer is one that is applied to the surface of the plant. ◼ Foliar uptake is important to aquatic plants and when nutrients are sprayed on foliage in horticulture and agriculture. Foliar fertilizer