The low recovery of soil phosphorus (P) associated with poor soil characteristics could be corrected through its foliar application if administered at proper growth stage with suitable concentration strength and appropriate phosphorus source. For this purpose a series of hydroponic, pot and field studies were conducted at The University of Agriculture, Peshawar to optimize foliar solution strength and its role on maize and wheat yield and phosphorus use efficiency (PUE) when applied at different growth stages and soil phosphorus levels. The hydroponic study was conducted in phosphorus-excluded Hoagland solution to evaluate plant phosphorus absorption from different foliar KH2PO4 solutions whereas the pot study was conducted to optimize foliar phosphorus levels in conjunction with various soil applied phosphorus levels. The 1st field trial consisted of “investigating the optimum growth stage of maize and wheat and number of sprays for foliar phosphorus application” while the 2nd field experiment was conducted on “supplementing effect of foliar phosphorus application in enhancing maize and wheat yields with saving fertilizer under calcareous soils” during 2013-14. The hydroponic study was conducted by spraying three foliar sprays of 0, 18, 36, 72, 144 and 216 mM KH2PO4 solution with 5 d intervals on 3 week old transplanted wheat plants cv Atta Habib into phosphorus-excluded Hoagland solutions. In pot study three sprays of 0, 45, 90 and 135 mM KH2PO4 solution were sprayed at 5 days interval on 20 days old maize and wheat plants grown at 0, 10 and 20 mg P kg-1 soil. In both cases the treatments were arranged in completely randomized design (CRD) with three replications and data on plant biomass, height, shoot and root [P] and PUE were recorded. Based on hydroponic study results, 144 mM KH2PO4 were sprayed at different growth stages of maize and wheat to optimize their suitable growth stages for foliar phosphorus in 1st field trial. In maize crop spray was given at four leaf, knee height, tasling and silking stages whereas in wheat it was performed at tillering, stem elongation, boot and anthesis stages as one, two and three sprays in both crops at given stages. In 2nd field trial, the maize and wheat were supplied with 0, 20, 40, and 60 kg P ha-1 as DAP applied either as broadcast or banding at time of sowing were sprayed with 144 mM KH2PO4 solution at knee height + tasling in maize and stem elongation + boot stages in wheat. In both field trials, the experiments were arranged in randomized complete block design (RCBD) with four replications and maize cv Jalal and wheat cv Atta Habib were the test varieties. Data on plant height, grains ear-1, grains spike-1, 1000-grain weight, grain and biological yields were recorded for both crops along with postharvest plant and soil NPK. Results of hydroponic study showed that foliar phosphorus application as KH2PO4 solution increased plant height, biomass and phosphorus uptake of 45 days old wheat plants grown in phosphorus-excluded iii Hoagland solution revealing the effective absorption of phosphorus from solution, its assimilation and translocation to other parts of the plant. No detrimental effect of over phosphorus concentrations from 0 to 216 mM was observed, however, the maximum plant growth or phosphorus uptake was recorded with increase in phosphorus solution up to 144 mM KH2PO4. The pot study, similarly, showed increase in maize and wheat growth and phosphorus uptake with foliar application of KH2PO4 at all levels of soil applied phosphorus. The response to foliar phosphorus increased with strength of KH2PO4 solution but decreased with soil applied phosphorus indicating more promising effect in soil phosphorus deficient conditions. The leaf [P] and PUE also improved with foliar phosphorus and increased with its concentration but at diminishing rate with soil phosphorus doses. Again no detrimental effect at any level of applied KH2PO4 was observed. The 1st field trial showed significant increases in maize and wheat yields, phosphorus uptake and use efficiency with 144 mM KH2PO4 foliar solution but the extent of response varied with growth stage and number of total sprays administered to crops. Knee height and tasling stage in maize and stem elongation and boot stage in wheat were observed to be highly responsive. Application of multiple sprays at different growth stages further increased the growth and yields but the combination of tasling in maize and stem elongation in wheat with other growth stages seemed to have more promising effect. The leaf phosphorus in both maize and wheat at the given stages was higher with number of sprays received but at maturity the higher phosphorus was observed when the spray was administered at knee height or tasling in maize and stem elongation or boot stage in wheat. The higher response at these critical stages could be associated with increasing demands of plant for P with rapid vegetative growth which were partially fulfilled by foliar sprays. It can be concluded that application of 144 mM KH2PO4 at given maize and wheat growth stages as a single or two sprays effectively enhanced crop yields and phosphorus use efficiency in the prevailing soil and climatic condition. In 2nd field trial significant increases in maize and wheat growth, yields and PUE were also observed through foliar application of 144 mM KH2PO4 solution sprayed at knee height + tasling in maize and stem elongation + boot stage in wheat. The growth and yields of both crops at lower soil phosphorus with foliar phosphorus was statistically at par or even better than respective next higher soil phosphorus levels suggesting decrease in soil applied phosphorus demand with foliar application. The overall results based on crop yield performance followed a pattern at each soil phosphorus level in order of banding + foliar phosphorus > broadcast + foliar phosphorus > banding > broadcast for almost all parameters indicating that lower recovery of phosphorus associated with broadcast could be corrected with foliar phosphorus as performance of broadcast + foliar phosphorus was better than banding + no foliar phosphorus. Tissue NPK concentrations improved with foliar KH2PO4 solution while post-harvest soil NPK content enhanced with soil applied P level coupled with foliar applied P. The results conclude that application of 144 mM KH2PO4 at knee height + tasling in maize and stem elongation + boot stage in wheat with 40 kg soil P ha-1 should be adopted for enhanced maize and wheat yields under calcareous soil conditions of the area. Keeping the promising effect of foliar phosphorus application, such studies should be conducted for other crops and locations for more widespread assessment, recommendations and adoption of technology.