When transplanting roses, dig the hole a good 6 inches beyond the stretch of the roots so it’ll be easier for them to extend straight out into the native soil. Spread roots as equally around the soil cone as possible, and cut off any broken bits and any that extend further out – you don’t want to have any curling around. Refill the hole with the original soil, adding no compost or other organic matter, and being spare with nitrogen fertilizers, as these hasten new foliage which may be damaged by late frosts and attract aphids. Create a watering berm a good foot away from the stem, and fill it three times to completely saturate the soil in the entire area and settle in the roots. Then add a 2” layer of organic mulch to the top to moderate soil temperature and gradually break down and distribute nutrients.
Feed plants with a slow-release organic formulation that’s about equal in N-P-K so plants grow consistently and slowly and have the nutrients to bloom well. Too much nitrogen at the beginning of the season will attract aphids, and at the end of the season will foster greenery that’ll perhaps be damaged by frost and not allow the plant to go dormant. In Southern California, this is especially important since we’ve had so little really cold weather over the last several years.
Reducing Potential for Problems
To make roses less attractive to aphids, make a point of NOT feeding with high-nitrogen fertilizer the previous fall and winter. It’s that wonderfully succulent new growth that the aphids are after. When they do appear, put on gloves and smash them – and leave the aphid-mush in place to deter future generations!
Spray the plants -- especially new growth -- with plain water from a hose with a spray head two or three times a week, making sure to cover leaf undersides. Roses that appear to be resistant to powdery mildew include Double Delight, Honor, Iceberg, and Cary Grant.
Enabling Longer-Lasting Blooms In A Vase
In a university trial, roses were cut when in bud and put in vases of 72-degree water, making sure no foliage was below the water line. Every two days, the stems were cut back about 1/4 inch, and new water was added. Blooms were judged for color, substance, retention of petals, and overall appearance. While all of the roses lasted at least four days, Olympiad and Touch of Class remained in good condition for a full nine days. Red, pink, and orange roses lasted the longest, as did those having many petals mainly due to their slower opening time.