Rose Care FUNdamentals
by Frank Brines, Master Consulting Rosarian
The latest weather report verifies what gardeners suspected: August 2020 was the hottest August on record. We also experienced many 90+ degree days in September. Many areas recorded consecutive days of triple-digit temperatures. This is way out of the average and made it difficult to adhere to the "normal" schedule of garden activities.
October promises to be unsettled too. Beginning with prediction of triple-digit temperatures accompanied by Santa Ana winds, with a slight cooling trend mid-month, and ending with "unseasonably" high temperatures again.
Mid-season pruning and fertilizing must be carefully coordinated with weather conditions. When temperatures are in the 90-100s range take care to not remove too much foliage because this can overexpose canes to the fierce sun resulting in sunburn which can damage or kill otherwise healthy canes or entire plants. Heat damage was widespread this year. Make sure to routinely check your irrigation system.
After I needed to interrupt and delay my seasonal pruning due to weather, and had sunburned canes and Chilli Thrips infestation, my roses have really rebounded. If there were fall rose shows in November, I'd have blooms to exhibit.
It's time to restart your fertilizing program if you're following my summer growing schedule. Make sure plants are thoroughly watered the day before you fertilize. I recommend organic types and alternating with one that includes fish emulsion. I suggest using a fertilizer that contains a greater percentage of (P) phosphate in relation to (N) nitrogen and (K) potassium to encourage stronger root systems and resistance to stress.
When temperatures are in the 90+ and you do not use organics, hold off fertilizing for cooler weather. If you use a fertilizer dissolved in water you can apply it right over the bush from top instead of at the base in a well. This application also does a foliar feed. A hybrid tea needs about two gallons of solution and should be watered in after a couple of days. Dry granular products should be scratched into the soil surface around the base of plant to drip line and then watered in. Apply at the recommended concentration on the label. If growing in pots, use half the recommended concentration but apply more frequently. Repeat every two weeks. Alternating with liquid and dry is most beneficial. The last day for fertilizing is 30 days before the "first frost date" which is around mid November in the Temecula Valley.
It is necessary that plants receive adequate water to stay hydrated. It takes only a few days of 90 degrees temperature for a bush to become seriously stressed and damaged without sufficient water. Hybrid Teas (Hts) can survive with 3 gallons of water twice a week. Make that your absolute minimum. The composition of soil effects water retention and the time for the soil to dry out. With potted roses this is even more critical. Four inches of good mulch will greatly reduce evaporation of soil moisture.
Assess garden conditions every morning. Look for wilted or dry crispy foliage. If discovered soon enough, douse severely stressed plants with plenty of water may save it. If you wait to inspect until afternoon or evening it may be too late. After a hot day most plants can appear a little wilted while still receiving sufficient hydration.
Routinely inspect the irrigation system to make sure it is delivering water as designed. Correct any problems ASAP: Your plant's life depends on it. Plants in clay pots require more water, plants in plastic pots are better. Soil in any type of pot material can pull away from the sides of the pot and water will just run through and out the drain holes in the bottom. This problem can be corrected by pressing the soil back against the inside sides of the pot when the soil is wet. Saucers under the pots may help too.
Spider mites are a common problem when hot, dry, dusty conditions prevail. This topic was covered in a previous care column which can be found at Temeculavallyrosesociety.org newsletter archive: look here at FUNdamentals for September 2013. Another hot weather problem is Chilli Thrips. See last months care column.
A valuable bi-monthly magazine which covers rose topics is the American Rose published by the American Rose Society (ARS). Go to www.rose.org for more information on obtaining it.