Dedicated to America’s favorite flower: the Rose!

Watering Your Roses

Ronald G. Schwerdt, Rgschwerdt[a]taol[dot]com, Consulting Rosarian

The key to growing bigger and better roses is maintaining the proper balance in the soil of air, water, and nutrients.

While there are many reasons why your roses did not perform, as they should last year, some problems have simple solutions while others are more complex. Many are simple physiological problems, and have no relation to an infectious disease. Many arise from problems with plants environment, such as: too much water or too little water, poor drainage, insufficient soil aeration, or a nutrient deficiency, etc.

To better understand water and its relationship to the soil, you should first understand how plants’ roots and stems utilize water in the soil. By implementing changes in the soil’s structure, you will allow for better soil drainage and an improvement in the air and soil movement.

Water is one of the most common compounds on earth, profoundly affecting all plant growth, both physically and chemically. The dictionary refers to water as a transparent, odorless, tasteless fluid. To a plant, it is the lifeline of its existence. Water is the means by which fresh air is introduced into the soil, since rainwater contains more oxygen than normal tap water. When the soil contains sufficient oxygen, combined with the proper nutrients, it results in a greater pulling in of moisture by the root system. This abundance of moisture is what puts that crispness in the petals of your finest looking blooms, and substance in the foliage.

A plant’s tissue is about 90% to 95% water. With this in mind, it is easy to see that without this vital compound, roses would not exist. While water is considered one of the main resources required to sustain life on the plant, it can also cause some significant changes to take place within the soil that should be addressed. These changes can trigger the start of retro-gradation in a balanced soil.

What happens when water is added to a soil? It forces carbon dioxide out of the soil. The carbon dioxide is generated by the plants roots and soil microorganisms. At the same time, it carries dissolved nutrients to the root zone where they can be absorbed by the fine feeder roots. Even though roots absorb fertilizers from the soil, they do not benefit from it at this time. It is only after fertilizer has gone through the cycle in the leaves (photosynthesis), that roots derive the benefits of the nutrients. This is one of the reasons why a deep soaking once a week is more beneficial than a light sprinkle two or three times a week.

Now that you know how water interacts within the soil, it is easy to understand how a rose bush standing in water because of inadequate drainage will affect that plant’s growth. While roses in containers require a large quantity of water, having their roots constantly immersed in water is the best way to kill the plant becaue it interrupts its supply of oxygen. The ideal situation is to have a soil retain as much water as the soil’s texture allows. This is referred to as “field capacity” and assures sufficient moisture to keep leaves turgid at all times.

What you want is an evenly moist soil, not one that is wet constantly (saturated). It is hard to overwater if there is good drainage. In container grown plants, wet roots are the number one cause of death.

In the soil, water is contained in three forms. One is hydroscopic water. This is water that is chemically tied up by the soil particles. The second form occurs when the soil is watered. The water gradually works its way down, filling the pore spaces with water and air – this is referred to as gravitational water. A soil is said to be at full “field capacity” when all the soil particles are coated with water. This is capillary water and is what the plant uses.

Even though the soil is kept moist with nutrients that are made available, plants can wither if they can’t utilize them. One reason for this is the constant and excessive use of chemical fertilizers containing a high concentration of mineral salts, which must be periodically flushed out of the soil. As these salts are leached out of the soil, various nutrients and trace elements are washed out with them. This may cause a deficiency in the soil, and those nutrients will need replacing. A high concentration of salts can draw water and nutrients out of the roots causing a nutrient deficiency that can cause the lower leaves on a bush to fall off, stunted growth and dehydration, etc. This does not mean you must stop, or even reduce your fertilizing program. What this means is you must water before, as well as after a fertilizer is applied.

Water and a soil’s structure go hand and hand. No matter what method is used to water you must have, or condition your soil into, one that is friable and well aerated so it can breathe. The key to watering is not how much you water, but how much moisture the soil is retaining. The more organics incorporated into your soil, the more water the soil will retain. This plays a major role in helping build the foundation for growing healthy plants. The pH of the soil and the pH of the water you use is also extremely important and is one of the determining factors in how well your roses grow.

Soils conditioned for optimum plant growth consist of about 50% soil and 50% pore spaces. These pore spaces between soil particles can be filled with either air or water or a combination. Normally these voids are filled with half air and half water. As water decreases, air increases. Too much or too little of either can be fatal to the plant.

In the Mid-West, July and August are the months when close attention should be given to the roses and soil. The weather is generally very hot and extremely dry, with not too much rainfall. Using a rain guage will give some idea on the amount of water the soil received during each rainfall. It is during this period you are thankful that you applied mulch; helping conserve soil moisture. If you don’t do anything else during these two months keep the soil moist by regular, deep soakings.

There are many ways to soak the soil. An easy way is to form an 18″ ring of soil about 4″ high at the base of each plant. If you have hilled up your plant with soil for winter protection, you can re-use this soil. Place the open end of the water hose inside for 5 to 10 minutes and flood the circle. Having enclosed rose beds; I lay the hose in a bed and flood it with 2″ to 3″ of water, on the average, about once a week.

Again, much depends on your soil’s structure, thickness of mulch, temperature, and wind velocity, etc. Besides being the cheapest watering system, it’s fast and efficient.

You can also use a drip or soaker hose, which will supply 1/3 to 2-1/2 gallons of water per ft. per hr., depending on your water pressure. By adding a water timer, it’s now as easy as turning a dial to set the system for the correct amount of time.

When a plant uses up available soil moisture faster than normal, the plant is put under stress; when this happens plants more likely than not attract plant pests and insects. While under this stress, plants that have suffered winter damage that was not noticeable in spring show the damage, resulting in some cane deterioration such as die back.

The same can be said about the foliage on a healthy plant. If it transpires moisture faster than the root system can absorb it from the soil, it will cause brown leaf edges from dead plant cells. All this leads to the number one object in these months. WATER, WATER, WATER.

Flushing the foliage with water early in the day gives the foliage a chance to dry, lessening the chances of diseases developing. Done every two or three days using a strong spray of water, over and under the foliage, will keep the bushes free of most plant pests. When spraying, adjust the setting so it produces a fine mist which will adhere to the foliage, rather than large droplets that roll off the leaves.

A rose bush needs one inch of water per week. Will this water reach the root zone where it can be utilized? This depends upon the soil structure. In a sandy soil one inch of water will penetrate about 12″, in a medium loam about 7″, and in a clay soil about 5″. All things being equal, your success in growing roses will be in direct proportion to the quantity of water in the soil that reaches the root zone.

How many gallons of water is this, and how long will it take to deliver one inch of water for a 200 sq. ft. rose bed? First you must know the water flow from your hose. A simple way to do this is to place your water hose into a container and measure the amount of water in the container after one minute, with no water being diverted elsewhere. Or you can use an in-line meter. For practical purposes, let’s say the rate of water flow is 4 gallons per min.

Known Factors:

1- One inch of water = 28,000 gallons of water per acre or (43,560 sq. ft.)

2- The rate of water flow is 4 gallons per min.

3- The area to receive one-inch of water is 200 sq. ft.

Unknown Factors:

1- The amount of time required applying one inch of water.

2- The amount of water being used.

200 sq. ft. x 28,000 gallons per acre = 5,600,000 gallons

5,600,000 gallons / 43,560 = 128.55 gallons of water used.

128 gallons / 4 gallons per hour = 32 min. per one inch of water.

In conclusion

Having read this article, you cannot help but realize that water is the essence of life for a plant. It plays the dominating role in all functions of a plant’s existence, at present and in future years. There is a parallel to this point; that was addressed in an article written on soil nutrients, which seems appropriate: “When asked about all the men in her life”, Mae West eloquently replied, “… Honey, it isn’t the men in my life, it’s the life in the men”. This same ideology applies to water and a plant’s survival. Repeated many times over … if you don’t do anything but water your plants they can survive, but without water they will die.

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