It is once again time for our "dry months" and the time of year that it is critical to keep your roses well watered. Roses, like many plants, are 50 – 90% water, one that plays a vital role for the plant. It is a major component of photosynthesis, it transports nutrients and carbohydrates throughout the plant, and keeps cells turgid (stiff). It is also necessary for keeping the plant cool via transpiration. Roses that are stressed from lack of water not only do not grow and flower as they do with adequate water; they are also more susceptible to attack by insects and disease. Water stressed plants can appear as dramatically wilted (loss of turgor to the leaves and flowers), they can demonstrate "crisped" foliage and flower petals; or they can just sulk - not wilting, or "crisping", but not growing or blooming at all.
For those that live in Marin, we know how precious water is as our main supply comes from either our seasonal rainfall, or the Russian River. We’ve seen strict water rationing at 50 gallons per person per day during the drought years, to skyrocketing water bills and mandatory conservation becoming the norm. In order to keep your plants well watered and keep minimize your water usage, it is helpful to understand the factors that determine how much and how often to water your plants.
Soil: The type of soil you plant in can have a significant effect on the amount of water it can hold. Sandy soils drain rapidly, holding little moisture while soils with a high proportion of clay absorb water more slowly and retain water much longer. Generally, the coarser the soil, the less water it will hold.
Planting site: The proximity of buildings and other heat retentive surfaces to the plant can speed up moisture loss, while areas under trees or other shade structures may produce an environment with higher humidity.
Weather: Air temperature, humidity and wind all play a role in the transpiration rate of roses; the higher air temperature and wind velocity, the more rapid the water loss. The higher the relative humidity, the more slowly the rate of water loss.
Sun exposure/light intensity: The more hours of sun each day, and the intensity of the light can result in increased transpiration.
Mulch: A heavy layer of mulch over the soil will significantly reduce the rate of water loss. Without mulch as an insulator, the soil is exposed to the elements of weather and results in a higher rate of water loss.
Plants: The size of the plant, and the manner in which they are planted can affect the rate of water loss. The larger the plant, the greater the amount of leaf surface to transpire. The more closely plants are spaced, the greater the overall plant density; the higher the density of plants, the more quickly the ground can be depleted of moisture.
Watering methods: Deep watering is preferable to shallow watering. The latter encourages root formation at the soil surface rather than deep in the soil. The deeper the penetration of water to the entire root zone, the less likely the impact of the elements of weather, thus the rate of water loss is slower.
Timing: It is generally best to water in the early morning if your garden does not get much wind, in order to reduce the opportunity for fungal diseases. If you do have wind, you can water in early evening, as long as any surface moisture has time to evaporate before nightfall.
There are no absolute rules to guide your watering. Don't rely on "rules of thumb" for watering your roses (like 2 inches per week); all of the items above can influence the amount of water you need. Try the old fashioned approach - feel the soil with your bare hands. If at the end of the day, the soil under your mulch is still moist, you don't need to water. Although roses LOVE water, take care not to over water; too much water in the soil fills all the available air spaces and cuts off the amount of available oxygen to organisms in the soil that help convert nutrients into forms plants can use. Without oxygen you can suffocate your plants.
Watering can be a pleasurable and relaxing activity – envision hand-watering plants in the early morning light while enjoying their beauty. It can also be daunting if you are limited on time, or have a large number of plants to keep hydrated. Automated systems, especially drip systems, can be a time and water saver if used correctly. They need to be sized (gallons per hour) correctly for the plant so that you provide even, deep watering. The down side to automated systems is that they water no matter what – come rain or shine, so that you need to be diligent about turning them off or modifying the cycle during cool or rainy periods.
There are a myriad of different devices you can use for watering – from little watering cans, to fancy hose end sprayers, sprinklers large and small, square and round to soaker hoses and more. Whatever system you use, be sure to water deeply and completely fill the root zone – it should soak in 8 – 10 inches. Light watering results in shallow roots that can’t handle even brief periods of drought or high temperatures. If you are using portable sprinklers, you can purchase hose end timers that will aid in conserving water. You can also add battery operated timers that attach at the hose bib that will turn the sprinkler on and off; these work very well if you have a small space, and don’t have to move the sprinkler around too much.
You can get recommendations on watering schedules from the Marin Municipal Water District website. They provide a weekly evaporation/transpiration (Eto) level for different areas in Marin. The ETo data on the website represents the amount of soil moisture lost during the week in the specified area based on weather conditions. They then provide a recommended watering schedule for different types of planting in order to replenish the soil moisture lost the previous week.
One side note about water quality – if you are using softened water that is treated by ion exchange, you can readily build up salts in the soil. The calcium that is removed from municipal water is generally replaced with sodium, Sodium doesn’t settle out and evaporation can cause it to accumulate in the soil, and result in burning tender foliage.
The use of anti-transpirants such as Wilt-Pruf or Cloud Cover can also help reduce your water usage. These are primarily wax-based based products that you spray onto the foliage of your plants to reduce moisture loss through the leaves. While this can be effective for conserving water (and also is beneficial in reducing some fungal diseases), it takes time and money – something to weigh against your water bill.
So, when planning your watering approach and schedule remember to:
- Know your environmental conditions
- Consider the weather
- Mulch, mulch, mulch
- Water deeply and aim at the roots
- Use a timer
Remember, water is a precious commodity – use it wisely!