How much, how long, and when to water are some of the most challenging questions when it comes to the efficient use of a drip irrigation system. In order to establish the amount of water needed for a plant's optimum growth, there are three main factors to consider: soil type, climate, and the size of the plant or container. Over watering is contrary to the goals of a gardener or farmer employing drip irrigation. Too much water results in an oxygen depleted soil that suffocates the roots and eventually rots them.
A plant only can absorb and only needs a certain amount of water for optimum growth. Water too little and you risk the plant dying of thirst, or at best, retarding its growth. Either extreme can kill your plant in short order.
Sandy Soils percolate quickly and water tends to run vertically (straight down). Drip emitters with a higher gallon-per-hour rating are best for this soil type as they will give the water a chance to spread horizontally. Set your timer to water often, but for a shorter duration.
Clay Soils hold water very well and cause the moisture to run horizontally (spreading out). If the percentage of clay in your soil is too high, it will retain water too long and squeeze out the oxygen. Oxygen is essential for the root system to be vigorous and the plant to thrive. Plants in clay soils should be watered less frequently. Lower gallon-per-hour emitters that are not spaced too closely will allow the water to seep into the soil with less runoff. Set your timer to water less often, but for a longer duration.
Loam Soils contain a high volume of broken down organic matter. The moisture retentive quality of loamy soils lies in the middle between sandy soils and clay soils. Plants will need to be on a regular watering schedule based on your climatic conditions.
Careful planning to make sure your plants get the proper amount of sun each day is a prerequisite to growing a beautiful and bountiful garden. Are your plants in a sunny location or in the shade? Do they get sun only in the morning or afternoon? These varying exposure factors will influence how much water your plants need and possibly even when to water. The times given below are general and will vary according to your climate.
Size of the Plant or Container
Small Pot - Plants in this size pot need to be watered daily but for a very short amount of time (1-5 minutes). Water coming out of a container is clear sign of over watering.
Small Shrub - Depending on the specific shrub's watering requirements, you might want to water every other day for 10 minutes or once a week for 30 minutes.
Large Shrub - Once established, a large ornamental shrub might need to be watered deeply once a week for 1 hour. If it's a Mediterranean species, it shouldn't require regular watering once it's established. If it's a species native to your area, no watering is necessary after the first year or two.
Small Tree - Even small trees should be watered to promote a deep root system. A Deep Drip Watering Stake is perfect for this job. At the same time the tree's shallow feeder roots shouldn't be ignored. For this, a few sprayers around the base of the tree or a ring of drippers run around the trunk will work well. Water before sunrise to reduce loss due to evaporation. Set your timer to water once a week for about 2 hours.
Large Trees - Large ornamental trees need watering less frequently, but more deeply. Here, in our hot, arid climate, we water large ornamental trees every couple of weeks for about 6 hours using a ring of Emitter Tubing. Mature fruit tree will need weekly water for about 4 hours.
Garden Beds - We can assume that the soil in any garden bed, raised or otherwise, will be close to the loam profile shown above, having been turned and likely amended prior to planting. However, if your local soil profile is predominantly clay or loam, any watering schedule will need to be adjusted accordingly.