Came across this informative research paper on fertigation of rose bushes:
The influence of two levels (500 ml and 250 ml) of NPK fertigation applied at 2, 4 and 6 days
interval on plant growth and flowering in two rose (Rosa hybrida L.) cultivars Amalia and Anjleeq
was studied as means of achieving better management, production and ascertaining NPK utilization
by the rose plants. Plant height, number of branches, number of leaves, number of flowers plant-1,
number of petals flower-1, leaf nitrogen, phosphorus and potassium percentage were maximum with
fertigation @ 500 ml at 2 days interval whereas more number of days were taken by the plants for
the emergence of first flower with fertigation @ 250 ml at 6 days interval.
Although all treatments were effective in improving rose growth and yield in both cultivars as compared to control,
however, the effect of fertigation @ 500 ml at 2 days interval was very pronounced particularly in
improving vegetative as well as the reproductive growth as compared to other treatments.
NOTE: fertilizer used was NPK 17:17:17 and solution concentration was 2 gm/litre of water