In the rose garden, minimize water use and maximize every drop

Roses are healthiest when grown in a garden that has a diversity of plants.
(Rita Perwich)

It is a given that water is essential for healthy, blooming roses. It also is a given that California is facing a drought. Last month, Gov. Gavin Newsom issued a directive mandating water conservation.

So how do we reduce our water consumption while looking out for our roses?

We can accomplish the challenge by taking steps to waste no water and ensure that every drop of water counts.

Water and plant health

Water is pulled up from the soil by roots and distributed throughout the plant. It is indispensable for the transport of nutrients to the plant and for photosynthesis to occur. The stomata — minute openings on the underside of rose leaves — cool the plant in a process called transpiration. This release of water by the leaves creates the “pull” that causes the uptake of water by the roots.

When there is insufficient water in the soil, the stomata close to preserve water. The result is a decrease in photosynthesis, which causes the plant to grow fewer and smaller rose blooms. Eventually, the plant will not put out any new growth and can become more susceptible to pest attack and fungal disease.

Plants require more water when it is hot. Ideally, in the summer, we would add to our irrigation run time and/or add an extra day of irrigation. In a drought, we need to consider steps to maximize our limited water and minimize plant stress.

"Frida Kahlo" floribunda is grown with various plants, including succulents and cosmos, both of which are low-water-use.
(Rita Perwich)

Making every drop of water count

There are many variables that affect the amount of water our plants need. These include the growing season, temperature, wind conditions, size of the plant, and composition of our soil and how well it retains water.

Plants that have been watered daily with light sprinklings are at a disadvantage, as they have shallow roots. Roses that are watered less frequently but with a longer irrigation run time develop a healthy, deep root system. This is especially important in drought conditions as it enables the plant to access more moisture from the soil and stay cooler and more hydrated.

Figuring out the minimum amount of water your roses need: Water in the early morning and time how long it takes to moisten the plant’s entire root system. Don’t irrigate again until the soil feels dry more than 2 inches deep, but don’t stress the plant by waiting to see wilting or drooping leaves and blooms.

One activity, multiple benefits: We should provide heat- and wind-stressed plants some relief by showering their leaves with water. This action, though not efficient water conservation, has a dual purpose, as water-blasting is one of the tools to keep pests such as spider mites and aphids in check. Avoid doing this during the hottest hours of the day to minimize loss of water to evaporation, but allow sufficient time for the leaves to dry before nightfall to prevent water-initiated fungal diseases.

Plant’s cooling system: In the summer, we avoid cutting long stems when deadheading or bringing blooms indoors, because leaves cool the plant through transpiration. They also shade the soil, reducing water loss. On the other hand, since taller plants use more water, you might consider shortening the height of your larger roses during a drought.

A Netafim drip irrigation system is laid on the soil around a rosebush and is covered with a 3-inch layer of mulch.
Netafim is an efficient drip irrigation system that delivers water to plants without waste. The evenly spaced internal emitters do not get clogged. The system is laid on the soil and is covered with a 3-inch layer of mulch.
(Rita Perwich)

Avoiding water waste

Use an irrigation system that conserves water: Drip irrigation systems like Netafim that consist of tubing with evenly spaced internal emitters are the most efficient water delivery system. They save a lot of water by putting out water at a much slower rate, usually a gallon or two an hour per emitter, and every drop of water is directly delivered to the plant’s root zone. The soil absorbs the water without waste and runoff, so the plant can utilize every drop.

In contrast, a sprinkler system’s output of water is a gallon or two a minute. These overhead sprays can lose up to 50 percent of water to evaporation. Also, in contrast to a drip system, which is laid out in a grid or a circle around each rose, there is no precision in water delivery with a sprinkler system.

Turn off the irrigation when it is going to rain: If you can’t remember to do this, install a smart water meter.

Watch for bad water management: Does your lawn get squishy and your soil muddy after you irrigate? This is a tipoff that you are applying more water than your soil can handle.

Bowser is framed by the scarlet flowers of "Wing Ding" polyantha blooming alongside Alstroemeria.
Bowser, the author’s dog, is framed by the scarlet flowers of “Wing Ding” polyantha blooming alongside Alstroemeria, which requires little water once established.
(Rita Perwich)

Check your irrigation periodically: Fix emitters that are broken or clogged, tubes that are disconnected, drip lines that have been chewed by puppies, and faucets and hoses that are leaky. Adjust your sprinkler heads if your walkway, sidewalk and gutter are watered when you irrigate.

Prioritize plants: Don’t waste water on underperforming roses and plants. “Shovel prune” them and save the water for the roses and plants you prize. Prune back or remove companion plants that are blocking water intended for your roses.

Balance water usage: Roses are not “water-smart” plants, but a healthy garden has a diversity of plants, including drought-tolerant ones. Lawns are the biggest water guzzlers and can account for half of a home’s water usage. Consider eliminating the lawn or a portion of it.

Reduce water use indoors and use the water you save on your plants.

Fertilize less in the summer for water conservation and pest control: Fertilizers stimulate growth, new growth requires more water, and tender new foliage provides a feasting bonanza for summer pests like chilli thrips. Last year, I applied an organic granular fertilizer at the end of June and did not fertilize again until the end of September. My plants remained healthy and had fewer pests.

Mulch: A 3- or 4-inch layer prevents the germination of weeds, which compete for water intended for your plants. This blanket of mulch laid on top of in-line drip irrigation also minimizes water loss due to evaporation and moderates the soil temperature, reducing root stress.

Rita Perwich is a member of the San Diego Rose Society, a consulting rosarian and a master gardener with UC Cooperative Extension.