Temperatures continue to be warm and it is important to adapt one’s approach to keep roses thriving as many plants (including roses) tend to shut down under extreme temperatures.
Don’t prune off the blossoms from the July bloom cycle; let them fade and wither. You can remove the spent petals, but leave the rest. The plants will respond by forming fruit – that’s what the rose hips actually are – and those will release hormones that slow the plant’s metabolism, signaling that it’s time to rest, not to put energy into blooms.
By doing so, you will prevent the plant from initiating new growth which would create stress during the harshest time of the year and the tender shoots will almost certainly be damaged by the heat. Keep your roses deeply watered and alive, and fertilize only lightly.
At this time of year, it’s best to shift whatever fertilizer you use to a higher level of phosphate to encourage root growth. As you probably already know, I prefer to use organic fertilizers. This is also a good time to make your second application of the year of magnesium sulphate (epsom salts): Apply three-fourths to one cup around the base of each plant, and scratch and/or water it in.
Do not forgo soil amendments such as a layer (at least 2 inches) of mulch. It’s true that such amendments provide a bit of nutrition, but not enough to kick the plant into a major growth spurt. Its main benefit is to help the soil hold moisture longer and spread it out in the root zone, as well as moderate soil temperatures. These are essential during dry, hot weather.
Mulch can include anything that shades the soil. I prefer to use composted mulch, available in bulk from various local suppliers, because it breaks down slowly and its nutrients are easily absorbed. Alternatively, you can also use a combination of leaves, grass clippings, coffee grounds, pine needles, etc. Just beware of creating a wet mat that prevents air circulation and can lead to sour fermentation. Pine needles are terrific because they tend to be very airy and allow water to penetrate easily, and they eventually break down to acidify the soil.
Beware of shredded wood products. I used them in a previous garden and was dismayed that it eventually bred mats of fungus that made the soil impenetrable to air and water.
Another big help during the hot weather is a drip watering system because it delivers water so efficiently to the root zone. Of course, you wouldn’t want to make radical changes to your plants’ watering regime in the middle of these hot months, let alone laboring out there in the sun. Wait until the weather cools down.
When you do install the system, you’ll want to survey your plants regularly to monitor the system’s output: Watch for individual plants that show signs of wilting or stress, and look closely to determine if that plant’s emitters are operating properly. If the entire bed seems stressed, increase the duration of the watering time.