What is the single most important factor in the short-term and long-term success of a new planting? If you said proper watering, you're right. Newly installed plants don't have extensive root systems like more established plants, so they rely on the moisture present in their root ball. Even drought-tolerant species will need a little help at first. As new plants grow and root out into the surrounding soil, they become stronger and more resilient to changes in moisture levels. But be careful - there is such a thing as too much water, especially in the slow-draining clay soils common in the Indianapolis area. Also be aware that just because the hose is running, it doesn't mean that the right amount of water is going to the right place. Follow these instructions to make sure your new installation is happy and healthy.
When to water
Dig into the soil 2-4 inches with your hand or a trowel. If the soil feels damp, don’t water, but check the soil daily to see if it's dry. Soon you will be able to use the weather and the look of the plant will help you judge if it’s time to check the soil again so you aren’t having to check every day. If it's 90 degrees in July, and it hasn't rained in three weeks, a new tree or shrub might need to be checked twice per week, while perennials should be checked every 2-3 days. If it's 60 degrees in April and it has poured rain for a week, you should be fine checking once per week at most. Eventually, you'll learn what your property needs, and you may not need to dig into the ground often at all.
How to water
When the soil is dry, water the plant slowly and deeply. This means you should water slow enough that the water is absorbed without running off. Leaving the hose running on full blast at the base of a tree won't help much because the water will run off instead of soaking into the soil. Instead, leave the hose on a trickle within the root ball of a tree or shrub or set up a sprinkler to cover the area with new plants.
Periodic deep watering is better than frequent shallow watering because it encourages the roots to grow further, and so it prepares the plants to be stronger and more resilient after you stop hand-watering.
Fifteen to twenty minutes of gentle watering should be enough for a shrub or very small tree. For larger trees, water the tree for a total of about 45 minutes, moving the hose once or twice to make sure the root area is evenly covered (you don’t have to move it if you’re using a sprinkler). Tree irrigation bags can be helpful in the short run if you know you'll forget to water a tree. Follow the instructions provided with the bag to make sure you're providing the right amount of water for the size of your tree. In very hot, sunny weather, tree bags can actually hurt your tree by trapping heat and humidity against the bark. In these conditions, consider removing the bag entirely or at least taking it off between fillings.
Annuals and perennials don't need to be watered as deeply as trees and shrubs since their roots are shallower. A sprinkler or a hand-held hose nozzle works well. 20-30 minutes is usually enough time for a sprinkler on perennials, 10-15 minutes for annuals. When hand-watering, I like to slowly move over the area in 15-30 circuits depending on how dry the soil is. Annuals will need water more frequently than perennials, because we focus more on growing those for a showy display above ground rather than a durable root system below ground.
Keep in mind that all these numbers for watering frequency and duration will change depending on soil type and moisture and weather conditions. When in doubt, check the soil in the way we described above.
Water newly planted trees and shrubs throughout the first year from spring until late fall. Trees benefit from an additional season of watering, especially if they were planted late in the year. Perennials are usually safe to stop watering after 2-3 months, but keep an eye on them. Annuals should be watered all season long. Temporary irrigation can be installed for the first few months or the first season so you don't have to worry about checking the soil. If you’re interested in having temporary irrigation installed after your project is complete, talk to your account manager. Water plants in later years when they look wilted, such as during droughts.
Water between late evening and early morning to reduce water loss through evaporation (but don't wait if a plant is wilting now!).
Avoid watering the leaves when possible. This can cause leaf spot diseases on some plants, especially roses.
Frequent light watering is only good for annuals, and even they prefer deeper watering.
Wilted leaves can come from too much water as well as from too little water. Always check the soil, especially in containers without drainage.
A thick layer of mulch will help conserve moisture. Just make sure you apply extra water so that the soil still gets soaked to a depth of a few inches.