I generally stick to monthly feedings with Plant Prod's rose fertilizer, but
some of my roses have been showing yellowing/veining/chrlorosis so I have
stepped it up as follows, with first feedings of all in mid-April coincident
with opening leaf buds

Thérèse Bugnet - strongest grower, earliest blooms but notable chlorosis,
increased feeding to bi-weekly with some but not complete improvement, will
try weekly feeding for three weeks then observe results. Also observed some
blackspot and mildew last year. Of all my roses this seemed to leaf out
unusually late, appears weakened from insufficient feeding last year.
Blanc Double de Coubert-seems to need bi-weekly to maintain healthy, waxy
foliage, otherwise seems to weaken and succumb to blackspot/mildew/aphids as
the summer wears on, about 1/3 winter kill but vigorous new canes developed
Morden Blush-some touch of cholorisis but monthly feeding seems enough, lost
lots of branches to winter kill however. One bush was about 3/4 winter
killed.
John Davis-no visible problems therefore monthly feeding
John Cabot-same
William Baffin-same
Alexander Mackenzie- same but lost a few big branches to winter kill

Snow cover is the best protection here in Zone 3B along with a final deep
watering after the leaves drop in the fall. Some recommend a watering in
winter if Chinook winds strip away all the snow, but am not sure of this
last strategy.