|
|
|
|
|
|
Irrigation Of all greenhouse tasks involved in producing poinsettias, irrigation is certainly the most difficult to describe adequately. There is both a science and art to determining when and how to irrigate, partly because of the many interacting factors affecting irrigation. Container size and depth, root substrate (medium) type, fertilizer program, plant size, time of year, and greenhouse environment all play a significant role in irrigation decisions. However, there are a number of important principles to consider in successfully irrigating the root substrate in which poinsettias are produced. Considerations The root substrates physical properties, as well as container size and shape, greatly affect irrigation. Root substrate selection is a very important part of irrigation decisions. A well-drained root substrate is less likely to be overirrigated; however, it is often more difficult to keep it well irrigated, particularly with larger plants. Irrigation requirements will vary greatly among different root substrates, and management practices and fertilization rates will need to be tailored to any substrate used. (See Root Substrate Quality for Poinsettias for more details.) Water Quality The quality of the water applied to poinsettia root substrate also greatly affects plant growth. Water containing a relatively large concentration of dissolved salts, like sodium, calcium, and magnesium, can cause excess soluble salts damage. Water with a high alkalinity (carbonates and bicarbonates) can cause plant damage by gradually increasing the root substrate pH over time. This increased root substrate pH can result in nutrient deficiencies, particularly iron. Water with a high alkalinity is particularly troublesome in soilless mixes and in smaller containers. The alkalinity of water can be corrected with the addition of phosphoric or sulfuric acid to the water supply. Specifics of this information may be obtained by having the water analyzed and recommendations made. It is very important to test the quality of irrigation water. The pH, alkalinity, and nutrient content should be checked as part of total water and fertility management program.
Water temperature is also important in poinsettia production. It should be close to air temperature for best results. Cold well water or hot water from overhead pipes or hoses exposed to the sun can cause plant damage. Leaching Past irrigation recommendations have specified that a sufficient amount of water (10 to 20%) be applied so the entire volume of root substrate is moistened and some leaching of water out the bottom of the containers occurs. Leaching prevents excess soluble salts from building up in the root substrate. This is still the easiest and most efficient irrigation method. However, with increased concern of run-off and water conservation, irrigation and fertilization practices are changing to reduce or eliminate leaching. If reduced leaching is practiced, it is still very important to moisten the entire root substrate volume totally to develop a strong uniform root system. Roots will not develop into dry root substrate. The fertilization rate can often be decreased by 25% is using a reduced leaching irrigation system or a flood irrigation system. Monitor the root substrate pH and electrical conductivity levels to ensure your fertility program is on target. Water should be applied early enough in the day so there is sufficient time for foliage to dry before dark. Otherwise foliage diseases like Botrytis may become a serious problem. Water Stress Water stress (drying) is used by some growers to control poinsettia growth. Maintaining the root substrate relatively dry for a prolonged period will not only suppress root growth, but will harden the plants. If the plants are water stressed during cutting establishment or around the time when the plants are pinched can result in fewer breaks. Plants under the beginning stages of water stress will have droopy leaves, which can progress to the edges turning yellow and necrotic and lower leaf loss under prolonged stress. Also, the drier the substrate is maintained, the greater the possibility of soluble salt damage to the plant roots.
Irrigation Methods Very few poinsettia growers depend entirely on manual irrigation with a hose. Although a hose with a breaker in the hands of a good grower is certainly a satisfactory system, the cost and time required to irrigate is unrealistic. There are a number of irrigation systems used in the greenhouse. There are several irrigation systems that can be considered for poinsettias. Spaghetti tubes, capillary mat irrigation, ebb and flood, and trough irrigation systems can all be used successfully with good management practices. Ebb and flood systems are the most expensive, except when they are on the floor of a greenhouse; however, they provide for easy and flexible plant spacing. Such systems can also be designed for recirculation of water and nutrients. Trough systems are somewhat less expensive than ebb and flood, but do not provide the flexibility in spacing. The spaghetti tube system is probably the most widely used for potted plants, particularly with larger size pots and hanging baskets. Four-inch or smaller pots require a large number of tubes per bench, making the system somewhat cumbersome. One large advantage to the ebb and flow, trough, and spaghetti systems over the overhead system is the foliage remains dry during irrigation and does not promote foliar diseases like Botrytis. This can be particularly important as the bracts begin to color. No irrigation system is completely automatic. Every system requires judgment in use and careful monitoring. No single system will fit every need. Growers will need to determine which systems best meet their needs in a cost-effective way.
|
|
|
| Home : Plant Part / Problem Type : Plant Structure / Problem Location : Symptoms / Cause |
|
|
