Spending your life amid gardens leads you to assess every green space… I have been able to realize that the most important factor for an area to look alive is watering. When we find that it is applied under suitable criteria, we behold amazing results… Regular plants properly watered are beautiful… Exotic plants watered too little or too much will die!
We know that water supply is essential for plants, it is a matter of survival, reason for which if we keep one or a thousand plants in an ecosystem different to their natural habitat it is our responsibility to provide them of water. At first, performing it manually would be a pleasurable experience that later would become a slaving task, because it becomes a routine, the failure of which is prejudicial to our plants.
Today’s technology allows us to affirm that implementing an irrigation system is relatively simple, after complying with certain technical criteria, which generally does not represent more than 20% of the total costs of the construction of a garden.
It is logical to think that the selection of the irrigation system to be used depends on the plants it shall serve. As in our case, we use ornamental plants for areas where different species will be combined, in contrast to agricultural irrigation where water is destined to a single species, watering becomes a more complex task.
There are some basic principles we must understand when irrigating:
AMOUNT OF WATER:
1.- Field capacity: it is the content of water or humidity that the soil is able to contain. This means that the “amount” of water that we can apply in an area will not depend on the plants on said area but on the capacity of the soil of bearing it.
2.- Wilting percent: it is the point of minimum humidity in which a plant cannot continue to extract water from the soil anymore and cannot recover from the water loss even though environmental humidity is surpassed. This means that plants wither when the levels of humidity are below the necessary and these values are set based on the soil and not the plants.
With these two factors present, we can establish the amount of water that we can apply to an area. There is a table that allows us to generalize and determine our irrigating pattern.
|SOIL TEXTURE||Field Capacity||Wilting percent||Available humidity|
|Sandy loam + organic material||29%||10%||19%|
|Well structured clay||50%||30%||20%|
Percentages presented herein refer to the “volume” to the soil to be irrigated, and depend on the depth of the root system of the plants; this means that if the roots of the plants to be watered reach 1 m deep (for instance, shrub-like plants) on 1 m2 the volume will be of 1 m3, which equals 1000 lt.
|Soil texture||Field Capacity||Wilting percent||Available humidity|
|Sandy||90 lt.||20 lt.||70 lt.|
|Sandy loam||140 lt..||40 lt.||100 lt.|
|Sandy-silt loam||230 lt.||90 lt.||140 lt.|
|Sandy loam + organic material||290 lt.||100 lt.||190 lt.|
|Loam||340 lt.||120 lt.||220 lt.|
|Clay loam||300 lt.||160 lt.||140 lt.|
|Clay||380 lt.||340 lt.||140 lt.|
|Well structured clay||500 lt.||300 lt.||200 lt.|
If the same criterion is applied for grass beds with roots of 10 cm of depth, the volume of soil to be irrigated shall be 0.1 m3 equivalent to 100 lt.
|Soil texture||Field Capacity||Wilting percent||Available humidity|
|Sandy||9 lt.||2 lt.||7 lt.|
|Sandy loam||14 lt.||4 lt.||10 lt.|
|Sandy-silt loam||23 lt.||9 lt.||14 lt.|
|Sandy loam + organic material||29 lt.||10 lt.||19 lt.|
|Loam||34 lt.||12 lt.||22 lt.|
|Clay loam||30 lt.||16 lt.||14 lt.|
|Clay||38 lt.||34 lt.||14 lt.|
|Well structured clay||50 lt.||30 lt.||20 lt.|
These tables show the “amount” that we can apply and how we can determine such amount.
Irrigation frequency is determined by the plants we grow, since they increase or reduce the amount of water according to their evapotranspiration rate, which at a time depends on the weather conditions of each time and place. The technical specific concepts more often applied to determine the farming irrigating frequency are: ETo: evapotranspiration calculated reference [a feature related to the climate of each location]; Kc: Crop coefficient; and ETc: crop evapotranspiration, where Etc= ETo x Kc.
Since in gardens we gather a big number of species, we must reach an understanding of the dynamics, which will originate more from trial and error than from applicable technical values. Nevertheless, it must be considered that plants requiring more water have higher evapotranspiration rates; thus, the irrigating strategy to be used is important to be pondered when locating our plants in a specific area so that we meet their water needs. Therefore, when combining different kinds of plants in a single area, we must use those with similar levels of evapotranspiration, so they use similar irrigating frequencies.
General criteria that must be considered to determine frequency of ornamental irrigation:
- Water excess is more prejudicial than water failure.
- Recently potted on plants require a higher frequency than those long established.
- Flowering and fruition stages require a higher frequency.
- Depth of root system: the more superficial; the more frequent.
- Sunlight exposure: plants exposed to the sun require a higher frequency than those in the shade.
- Wind rate: the windier; the more frequent.
- Environment humidity (air): If air is dry, frequency shall be high.
- Soil texture: sandy soils require a higher frequency than clay soils.
- Altitude over sea level. The higher the altitude, the lower the frequency.
- Plant roots need to breathe, therefore, it is important that we allow air circulation in the soil. This means that we must permit soils to “dry”, so that water can go in, but never below the permanent wilt percentage.
If conditions are favorable (ex. in Caracas): in an already established crop, with temperatures ranging from 22’ to 33’ C, relative humidity between 70 and 80%, winds lower than 20 km/h, altitude of 1000 m.s.n.m., with sun exposure between 10:00 am and 4:00 pm, we could calculate that a frequency of 4 days a week (Monday, Tuesday, Thursdays and Fridays) can ensure survival of any ornamental crop we have. From this point we shall start our observations and adjustments according to the specific requirement of each garden.
Other irrigation criteria in established gardens are a minimum frequency of 3 times a week or a maximum of 5 times a week.
To determine the irrigating schedule needed, we must consider the relative humidity of the location. If humidity is high, we must privilege the hours of daybreak and morning, and thus we avoid proliferation of fungus diseases. Now, if weather is very dry and water volumes are in short supply, we should rather irrigate in the afternoon or at night. In general, we may say that it is not convenient to water the plants between 10:00 am and 4:00 pm. There are always exceptions, such as orchids: they like to be watered at noon, this stimulates flowering! Shade zones without direct sun exposure can be irrigated any time.