Last week, regarding summer care of roses, I briefly recommended fertilizing monthly and responding promptly to signs of insect or disease problems. Those are constructive actions, but there’s more that can be done to help your roses to flourish!
Fertilizing roses in the summer is important if they show signs of nutrient deficiency, such as weak growth. Provide a light application of fertilizer with an emphasis on phosphorous.
Recall that fertilizer labels indicate the percentages of the three principal ingredients: N – nitrogen (promotes the growth of leaves and vegetation); P – phosphorus (promotes root and shoot growth); and K – potassium (promotes flowering and fruiting). I have used Dr. Earth’s Rose & Flower Fertilizer (5–7–2), but you could find other very good fertilizers at your local garden center. As always, follow supplier’s recommendations.
Yellowing foliage probably indicates an iron deficiency, which calls for spraying with a liquid iron supplement.
The most common pest of roses is the aphid, which suck the plants juices from buds, stems and the underside of leaves. They can be washed away with a forceful stream of water, or treated with a spray of insecticidal soap, such as Safer® Brand insect killing soap.
I routinely grow Society Garlic (Tulbaghia violacea), which has a garlicky fragrance that seems to confuse or distract aphids. It really works!
Weekly watering will keep roses healthy during the summer months. Water roses at ground level to keep foliage dry and avoid fungal diseases. Use organic mulch to minimize evaporation and discourage weeds.
Deadheading spent blossom will promote new blooms. Cut them off close to a close to a cluster of five leaves; some experts recommend cutting at the second five-leaf cluster, to encourage growth from a stronger stem.
Remove suckers at the base promptly. If possible, pull them off from the rootstock; otherwise, cut them below the soil surface.
Deadhead other spring-blooming plants. This practice improves the appearance of the garden, promotes new blossoms from many plants, and reduces the spread of seeds (which might or might not be desired).
Currently, I am deadheading two larger plants: Corsican Hellebore (Helleborus argutifolius) and Mediterranean Spurge (Euphorbia characias, subsp. wulfenii).
Here are Hellebores in full bloom, standing upright.
And here they are laying over:
Here are the Euphorbias, fading:
These plants are quite different but still have common characteristics: they both produce large, dense clusters of flowers on thick stalks that bend over as the flowers fade to drop seeds away from the base of the plant. Both also are prolific self-seeders, if allowed.
At the same time, they produce new growth that limits access to the base of the flower stems. I have found a telescoping pruner to be invaluable in this task. A “cut & hold” model would be ideal.
Enjoy your garden in the summer!