Keeping Roses Healthy in a Drought

Drought – it’s a scary thing, especially when your only source of water comes from seasonal rains and they don’t materialize.  We had record rainfall in the winters of 2017 and 2019 but his past season was relatively dry. While we have adequate water to get us through this season, it’s always a good idea to look for ways to use this precious resource wisely. What does that mean for our prize roses?  Aren’t they water hogs that need lots of water to survive?  Not necessarily.

Nature produces all types of plants with varying water needs; there are drought tolerators – plants that are able to survive and even thrive with minimal water like many of our California natives. There are drought avoiders, plants that have very deep taproots that allow them to grow well during limited rainfall – many species roses fall into this category. Our modern garden roses are drought evaders – they avoid water stress by dropping their leaves, producing small blooms, or becoming virtually dormant, and in this stressed state, become prime targets for pests. 

The volume of water a rose plant needs depends on a number of variables; the age, size and location of the plant, the nature of the soil it is growing in and the air temperature, humidity and wind conditions to name a few. While roses perform best with ample water, they can make it on much less; the plant may not grow or produce many flowers during the hot summer months, basically going dormant until cooler temperatures arrive, but they will survive.

Often watered frequently for short amounts of time, garden roses develop shallow roots and have a tougher time during times of reduced water availability, often wilting or exhibiting leaves with brown, dead edges. But it’s not how they start out.  Most modern roses are grown in production fields located in super-hot areas like Bakersfield, California and Phoenix, Arizona. They are deeply watered only once per week (furrow irrigation for about half a day), no matter if the temperatures are in the triple digit range for weeks. And they do just fine. 

World renowned rose hybridizer Tom Carruth, now Curator of the E.L. and Ruth B. Shannon Rose Collection at the Huntington in San Marino, California, is responsible for a garden with more than three thousand rose plants. Like most rose growers in the state, he’s had to grapple with reduced water supply while keeping plants looking great at this public garden.  He notes, “We have already cut water usage by half (the garden was extremely overwatered) and the plants are now trained to seek water. I think we will water less frequently but more deeply with a hand water supplement to any unestablished plants.”

Care recommendations provided by the now closed Vintage Gardens nursery reflect Carruth’s perspective; “In our summer-desert climate in California we have no rain for a space of four to six months each year. Like many woody shrubs, roses can bury their roots very deep in the soil, accessing hidden moisture through the summer and fall.” One of the best things you can do for your roses is to force them to develop deep roots, ones that extend 18 inches or more into the soil. 

To maximize your water use and keep your roses healthy consider:

Reduce what you need to water:  Take a hard look at your roses – are they all producing the abundance of healthy foliage and blooms you desire, or do you have some that are stingy with flower production and magnets for mildew and other disease?  Give them the boot!  Don’t waste precious water on plants that are performing.

Smaller may be better:  After the big spring bloom, trim plants back significantly to reduce their overall size. The more foliage on the plant, the more water it will require to remain healthy.  You may lose some bloom (it supposedly takes 35 roses leaves to produce one rose blossom), but come fall with its cooler temperatures, you should have a good crop of flowers.

Leave the leaves:  Whether cutting roses for bouquets or deadheading spent blooms, leave as much foliage on the plant as you can. While the leaves require water to stay hydrated, they’re also the cooling system for the plant, needed during high temperature days, and provide shade for the base of the plant, potentially reducing moisture loss from the soil.   

Go light on fertilizer:  Many rose growers apply high nitrogen chemical fertilizer monthly spring through early fall; this stimulates growth requiring the plant to use more water. And the resulting succulent new foliage is an attractant to aphids. If you fertilize, use a less soluble form of nitrogen and apply it in small portions throughout the season rather than all at once, Organic materials like manure, fish emulsion or blood meal, or slow-release fertilizers fill the bill. Or think about skipping (or at least reducing) the pest cycle this season and don’t add any supplemental fertilizer at all.

Timing can make a difference:  Water during the early morning hours when temperatures and wind speed are the lowest, and where possible, stretch the time interval between irrigations.  Roses do best when 50% of available water is depleted between irrigations. Don’t water based on the calendar or a schedule, watch the weather and your plants, and monitor moisture in the soil. 

Check your tools: No matter what system you use to water your roses, make sure they’re in good working order.  Fix leaky hoses or faucets; check drip irrigation, sprinkler systems and timing devices regularly to ensure their proper operation.  If you water by hand, have an on / off valve at the use end and turn the water off when moving between plants.

Technique makes a difference:  Water your plants slowly and deeply; apply water only as rapidly as the soil can absorb the water. Divide your watering cycle into shorter periods to reduce runoff and allow for better absorption every time you water. Apply water within the “drip line” of the plant (that imaginary line of from the outermost leaves of a plant down to the soil).

Mulch, mulch, mulch: By adding a layer of mulch to the soil in the spring, you can moderate soil temperature, reduce water consumption and reduce weeds.  Mulch is basically a protective blanket placed over the soil and can be either an organic or inorganic material. The amount of mulch you add depends on the texture and density of the material you’re adding and the quality of drainage of the soil your covering. A good rule of thumb is to add two to four inches of mulch. Remove weeds first and then carefully spread an even layer of mulch, keeping it a few inches from the base of the plant. 

Watch out for weeds:  Weeds will compete with your roses for precious water.  Remove them by hand (and get the entire plant when they’re small before they go to seed).  To prevent weeds, put down a fabric barrier with a layer of mulch on top.

Protect against pests:  Spider mites thrive in dry and dusty conditions. Add warm temperatures and their populations can explode, defoliating a rose plant in short order.  Forceful spraying of leaves, especially the undersides, is a good method for keeping these pesky critters at a tolerable level.  With limited water, get creative!  Invest in a two or five gallon pressurized sprayer (the kind used to apply pesticides).  Collect that clean cold water that would otherwise go down the drain while you’re waiting for the shower to warm up, fill up the sprayer, pressurize and blast the little critters off your plants. Knocked to the soil level, these pests aren’t very successful at getting back on the plant. As with any application of water to rose foliage, do it early in the day so leaves can dry.

With a little planning and extra care, you can have healthy, productive roses all the while reducing your water use. As Carruth points out, “A weakened plant is always more prone to problems. Let’s hope we don’t have to discover all the complexities.” 

By Nanette Londeree, Master Rosarian

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