Water roses deeply as temperatures rise

Gardeners must become water-wise and learn as many ways as possible to use water efficiently. Some districts have restriction on how and when water can be used for irrigating landscape. Water agencies advise customers to be conservative this year as supply is still limited and even purchasing water from other regions is difficult for the same reasons.

There are a few things gardeners can do now to provide some relief for their cherished roses once the weather gets really hot. First, as hot weather approaches, cut back on fertilizing established roses; it will encourage them to slow down for the hot summer. Second, water roses deeply as temperatures rise. Next, hose off roses in the early morning to increase humidity and control spider mites, which are found mostly on the underside of the leaf. A strong forceful spray from below will be needed to dislodge these mites. Then give a downward shower rinse to wash them away. Spider mites usually appear when the seasonal temperatures have been hot. Also, keeping vegetation trimmed to approximately 8 inches from the soil level will help as well.

Typical mature, full-size hybrid teas in Southern California soil require about 6-9 gallons of water a week when temperatures are high. As temperatures rise into the 80s, those roses require about 9 gallons of water per week. In the 90s, the rose requires about 12 gallons or more per week. These figures are rough and based on the amount of water needed to maintain the highest level of show quality blooms: A rose can stay alive on considerably less. But during summer heat, I don’t even try to have show quality blooms.

The past few years of drought experience has made gardeners aware that they must be watchful and learn how to efficiently manage the amount of water applied to yards. The strategies I will discuss here are delivering water efficiently, keeping water in the soil using mulch and allowing roses a summer dormancy period.

First, deliver water efficiently. Drip systems provide the most efficient way to deliver water to roses because such systems don’t produce a spray that can be carried away by the slightest breeze and because they deliver water slowly, allowing it to soak deep into the root zone rather than running off.

Be sure the drip system is in good shape before going on to the next step, which is to cover it with mulch. Open each irrigation valve one at a time and inspect how it is performing. Repair any leaks, including emitters that are spraying from their attachment point on the tubing – if so, remove the emitter, insert a “goof plug” and install a new emitter an inch or two away from the original one. My gardening friends are recommending the more efficient drip system called Netafim. This product has pre-placed pressure regulating emitters at different distances apart. Find the information at http://www.netafimusa.com.

One more thing is to estimate the volume of water the system is delivering, better managing its use. For example, if every rose has two emitters, which it should have in the typical drip line system that deliver 8 liters or about 2 gallons per hour, then to deliver 4 gallons to the plant it needs to run the system for an hour. It should work well in a typical loam soil. The water needs to soak down at least 12 inches for optimal rose health. A loam soil doesn’t allow water to just run through it, so irrigating for an hour at a time can be fairly efficient. On the other hand, if soil is particularly sandy, which allows water to permeate more quickly, an hour of irrigation may waste some of that water, and it might be better to run the system twice a week for half as long. Experiment. After all, gardening is a scientific pursuit.

Next, mulch well. In past columns, I have been advocating the application of a deep layer of mulch. Mulch provides many benefits. It moderates the soil temperatures, retains moisture, allows it to spread more uniformly throughout the root zone, discourages weeds and maintains a soft soil surface while enriching the soil nutrients and biomass. A 4-inch layer of mulch is recommended. I highly suggest composted mulch. There are many materials to use however and experimenting with a variety of them will probably lead to the best results. Don’t mix them in any one garden bed though.

One material that some gardeners have in abundance is pine needles. They provide an airy cooling barrier and break down very slowly to impart a more acidic soil environment which makes mineral nutrients more available to plants. Another material is any size of wood chip specifically intended as mulch; I recommend the finer cut forms. Possible drawbacks are if it was not specifically manufactured for garden use, there is the potential for matting due to fungal growth, which can make the wood chip layer impermeable to water and increase the need to apply added nitrogen to break down the wood fibers. I’m not an advocate for the dyed wood products.

I prefer composted mulch that is light and fluffy so it doesn’t pack down and that contains a higher proportion of hummus so it slowly integrates with and enriches the soil. One drawback of composted mulch is that after several years gardeners may find that their garden soil level has risen. If this increase ends up burying the bud unions, it can be helpful to “lift” the rose – essentially, digging to release a large root ball, levering it up, filling in several inches of good garden soil beneath it and resetting the root ball in the hole or maintain a clear well around the base of the bush.

Whatever mulching material is chosen, be careful to not apply it up to or over the bud union. Leave an area around the base of the plant of about 12 inches in diameter. If distance can be maintained, then as the composted mulch disintegrates it will not raise the soil level around the bud unions.

Lastly, summer dormancy is recommended. Allowing roses to go dormant during the hot summer months will reduce water use as well as the stress on the plants. They won’t be missing out much because roses that are allowed to power through the summer put out blooms of mostly poor quality with burned petals and leaves. So as roses complete the current bloom cycle, remove only the petals as the flowers fade – do not deadhead them – that is, allow hips to form. It will discourage new growth and flower formation, thus reducing demand for water. Remove any fallen leaves and discard them along with the petals into a green yard waste bin – do not compost them. It is always a good practice to keep the garden clean in order to reduce fungal diseases and insect pests, particularly in hot dry weather. Do not remove burned leaves because they provide shade for the cane which can be damaged or killed by sunburn. Discontinue a feeding program – do not encourage growth at this time because it will only stress the bush more.

In summary, until at least September:

● Make sure the water delivery system is operating efficiently.

● Apply 4 inches of mulch over the entire bed.

● Remove petals as flowers mature.

● Allow hips to form.

● Do not prune or cut back.

● Leave brown leaves on the plant.

● Do not feed.

Potted plants will require more diligent watching, resources and attention to what they are experiencing during this period. Learn to listen to the plants and observe their reaction to the elements.

Doesn’t look like much work, right? Well, since gardening will be easy for the summer, go visit the Rose Haven Heritage Garden, 30592 Jedediah Smith Road, in Temecula. The cross street is Cabrillo Avenue. Also, visit the website http://www.TemeculaValleyRoseSociety.org.