It has been a great summer, the monster rainfall of this past winter and spring a distant memory, and the yard looks wonderful in May and June. You are pumped up about how well your gardening skills have developed. You are getting a sore shoulder from patting yourself on the back in celebration of the glory of your garden. –You smile to yourself and kickback on your rose care diligence. “Where is my wine?” Then July rolled around. Your “wining” has turned to “whining.” “What happened to my roses? The leaves have turned brown and they look awful.”
Well, you are human, you think when you fix something in the garden, it stays fixed. Well, you are wrong, Buttercup. Mother Nature lives in your yard too. In July she said, “It is time for a little humility for our green-thumbed person. I think I will cook their plants.” What happens when it turns from spring weather to Death Valley weather in your Napa garden? Cooked plants happens. This dose of truth from Mother Nature may hurt, especially when it catches you off guard, even for a day or two. This is the deal, roses do like 6-12 hours a day of normal sunlight–the key word being normal. Roses can take pretty much any amount of sun, but when it gets into the 85-90's things change. It gets even worse if you have some of your roses in containers like I do; you have to be ready for the heat beforehand. You avoid gophers with containers (gopher issues are fodder for another column) but encourage irrigation issues. If you guess wrong, you will find:
#1 Wilting is the first sign of heat stress. It shows up in the older leaves first near the top of the plant. It is a normal protective reflex of the rose to wilt/curl their leaves to preserve moisture. If you have a drip system on a timer, but you have not adjusted for the hotter days, you will get wilting and dropping of leaves sooner as the root ball is probably too dry and water will not penetrate to the drying roots. When the roses start to wilt, they also become susceptible to diseases too. Black spot, rust, and other fungal infestations can attack the leaves. Even spider mites or scale can take advantage of the problem. Deal with these threats quickly or you can lose all the leaves which will take weeks to regrow.
#2 Browning of edges as the picture above shows, the edges / tips turn brown. It is a different brown than fungal infestation; it is clearly a leaf that is baked. You have to remove these as they will not come back. Soak the root ball and make sure that it does not dry out again. Spray the leaves as needed. Use a meter if necessary. If the rose is in a container, you may have to soak the whole container into a tub filled with water, to fully rehydrate the ball–don't drown the ball, just get it thoroughly wet. If it is too big to lift of move, run a hose at a low rate into the container until it is saturated. If the ball is in the ground, using a shovel or trowel to loosen the soil will help get the water down deeper.
#3 Cover if possible when it gets over 95 degrees, placing a cover, shade cloth or umbrella over the plant. This is needed as the bush will no longer be able to go through photosynthesis and it no longer can efficiently respire. Blooms stop or become smaller, the leaves weaken and evaporation through transpiration speeds up and recovering from wilting becomes less likely.
#4 Mulch: If the damage is done or if you are ahead of the problem of heat stress, you should consider mulching. A layer of mulch about 2-3” thick around the plant will protect the bush. This will protect the root ball from the drying effects on the soil and prolong the retention of what water is available. The mulch will hold water between watering cycles and it will reduce the amount of weeds below the plant. Using a moderate spray of water in the mornings will get the bush ready for a hot day, but it will also remove dust as well as pests from the plants. In normal weather situation, it is not recommended to spray the leaves of roses due to fungal disease issues. However, in the scorching hot days, keeping the leaves cool is the lesser of two evils. 
Remember to toss plant debris into your city compost bin and not your own compost pile. The Napa City compost center produces higher temperatures to destroy the spores while your backyard pile will not do so. When it comes to add mulch, consider getting it from the Napa recycling center.
If you have questions about the Fuller Park Rose Garden and the Master Gardeners (MGs) who maintain that Rose Garden, the MGs are usually in the garden the first Sunday and third Thursday of each month between 10:00 and noon, weather permitting.
Napa Master Gardeners are available to answer garden questions by email: mastergardeners@countyofnapa.org. or phone at 707-253-4143. Volunteers will get back to you after they research answers to your questions.
Visit our website: napamg.ucanr.edu to find answers to all of your horticultural questions.
Photos by Bob Niklewicz
