Water is important for plants, yet most people give little thought to water quality. A pH of 7 is neutral, more than 7 alkaline, and less than 7 acidic; pH is important because many minerals have trouble entering roots at the wrong pH. Ideal pH is 6-7, slightly on the acid side. Other chemical properties of water can also cause problems. I water my plants with well water that is very hard. To compensate I repot often, at least once a year. Soluble salts build up in potting media and eventually reach toxic levels. Repotting gets rid of these salts and also removes dead roots that accumulate in quantity after a cactus goes through its winter resting period. These dead roots are the perfect environment for plant infections. Most plants start dying first in the root zone where it cannot be seen until it is too late. For these reasons, I advise repotting cacti often.
There are three ways to water container-grown plants. Overhead watering is usually done through an attachment to a hose or a watering can called a rose. The rose breaks water into soft, misty streams. A disadvantage of this method is that plants may develop disfiguring spots from minerals in the irrigation water. The second method is bottom watering. Pots are usually left sitting in pans or saucers and water is added to the pan or saucer. Bottom watering works well but has a couple of disadvantages: each container has to be removed from its pan or saucer at least monthly for leaching, and it is important that any excess water not taken up by the potting medium be removed before too many hours pass. The third method is to water each plant at the soil line. This is the method I use and find that its only major disadvantage is that it takes longer to water. I turn this into an advantage by enjoying each plant as I give it a drink and looking carefully for any sign of health problems that will require action.
A good-quality watering can is all that is needed for smaller collections, but as plant numbers increase, some type of system will be necessary to improve watering efficiency. I use a 35-gallon (130-liter) plastic garbage can, a submersible sump pump, and a 30-ft (10-m) garden hose. Attached to the end of this hose is a metal watering wand with a trigger to meter water flow. Each plant is watered at the soil line.
How often should one water? Simply plunge your finger into the soil mix. If it comes out with soil particles sticking to it, the plant does not need water. If no particles are clinging to the skin, the soil is dry and water is needed. I generally water every 7-10 days during the growing season, and about every 4-6 weeks during dormancy. More cacti are lost as the result of untimely application of water than for any other reason. Even though cacti rest during their winter dormancy, the roots continue to grow all winter. Growing roots need a little water throughout the winter or they will die. Lack of water will not kill cacti during their dormant period, but certainly there will be root loss and stunting that may not be necessary.
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