How heat affects the watering and fertilizing of rose bushes

Frank Brines

ARS Master Rosarian

Well, I always enjoy looking back to last year's care column for the month. In October 2020 was the hottest Oct. 1 on record with 102.8o. According to Accuweather, the average normal temps for Temecula are high 83o and low 54o. The average for 2020 was high 86.8o and low 55.7o. Predictions for October 2021 are mild 90's the first week decreasing to 80's by month end. Just to show the climate is changing.

All this is helpful for garden activities this month. 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.

Some gardeners experienced Chilli thrips, I was one of them. My garden was attacked at the end of September. I missed timely spraying and had to prune more heavily than normal.

Rose Societies are beginning more normal meetings and shows. Orange County Rose Society is sponsoring a show Oct. 23 in Yorba Linda at the Nixon Library. There are possibly two shows in November. The closest one will be in Palm Desert Nov. 13. I hope my roses will repeat that soon so I will be able to participate. I think everyone should visit a show when it is so close, learn what does well in local areas, find a new variety for your garden, and get acquainted with other rose enthusiasts.

If you missed starting your fertilizer program last month, it is time to restart now 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.

This time of year 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. A soil test may indicate that you may need some other mineral to make the added phosphate available or if needed.

When temperatures are in the 90o+ and you do not use organics, hold off fertilizing for cooler weather. If you apply a fertilizer dissolved in water early in the day 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 the 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 90o temperature for a bush to become seriously stressed and damaged without sufficient water. Hybrid Teas can survive with 3 gallons of water twice a week. Make that your absolute minimum. The composition of soil affects water retention and the time for the soil to dry out. Four inches of good mulch will greatly reduce evaporation of soil moisture. With potted roses this is even more critical.

Gardening makes morning people out of us as that is the best time to assess garden conditions. Look for wilted or dry crispy foliage. If discovered soon enough, dousing severely stressed plants with plenty of water may save it. If you wait until afternoon or evening to inspect it may be too late. After a hot day most plants can appear a little wilted while still receiving sufficient hydration so afternoon checking would give you wrong information.

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 and Chili thrips are common problems in hot, dry, dusty conditions. This topic was covered in September care column: https://www.temeculavalleyrosesociety.org/nl/NL202109.shtml#h12

A valuable bi-monthly magazine which covers rose topics is the American Rose published by the American Rose Society (ARS). Go to http://www.rose.org for more information on obtaining it.

When you have a moment to spare, or feel the need to get away, or when the day cools down, take your favorite beverage, a picnic basket, and visit our local one-of-a-kind Rose Haven Heritage Garden, 30592 Jedediah Smith Road, Temecula (cross street is Cabrillo Avenue). Also, visit http://www.TemeculaValleyRoseSociety.org.