What’s the best way to irrigate new plants?

I installed a new garden last year and I am wondering if I should start watering the plants installed last spring. My contractor installed some more plants in early April this year.

— Hector Jones, Addison

May has been a dry month, with some cool temperatures helping to mitigate the lack of rainfall. The soil conditions in many gardens are running on the dry side this spring, so giving your new plantings some more focused attention to watering in the coming weeks is a good idea. The established plants in my garden at home have not shown any signs of drought stress yet. The recent hot weather did speed up the drying out of gardens and increased stress on plants. It’s difficult to give you specific instructions for watering, as there are many variables based on a garden’s site conditions. Gardens with sandy and well-drained soils will need more frequent watering to get the plants established, as the soil will dry out more quickly than heavier clay soil will. Different types of plants prefer different levels of moisture , while perennials planted in a shady zone may be competing with tree roots for water. The amount of sun and shade will also influence how much water is needed for those garden areas. Different areas of your garden may dry out at different rates.

The established plants that have been growing for more than three years in your garden are most likely fine and do not need supplemental watering. Many plants installed over the last three years will benefit from additional water this spring and summer, with those planted last year and this year getting priority attention. I just watered some shrubs that I had planted early last fall, as there has not been enough rainfall to water them adequately for their stage of establishment this spring.

Spot check the soil at the base of your plants to see how much soil moisture is present to guide you in whether to water. Water stress is harder to see in the foliage during the early spring season. Water trees and shrubs were planted as balled and burlapped trees with a hose at the base to thoroughly moisten the root balls during the first one to two years of establishment. You should not rely solely on a sprinkler system. Even recently installed perennials will benefit from an occasional deeper soaking with a hose while they are getting established in their first couple of years. The foliage of evergreens can shed water from a sprinkler to the outside of the root ball, leaving it dry. As the tree establishes over the first two to three years, the roots will grow into the surrounding garden soil. Generally, one thorough watering per week will suffice for new balled and burlapped plants during the first year. Also monitor to make sure that you are not overwatering, as I have seen gardens with sections that are very wet with soggy soil even during dry periods — a sign of overwatering, which can also stress and kill plants.

Plants grown in containers before planting need more frequent, lighter watering (two to three times a week, depending on the weather and planting site) for a few weeks until they establish roots out into the native soil. The growing medium used in containers will dry out quickly, especially if the plant has an extensive root system. If you are using an automatic sprinkler system or watering with a sprinkler attached to a hose, check that all the plants are getting adequate water by monitoring the soil and spot-checking the plants’ root balls. Don’t assume that your sprinkler system is providing the right amount of water. Monitoring the plants and the soil moisture will help you provide the optimum amount of water for your new garden plants.

Many gardeners are seeding lawns now. Proper watering is critical to success with seeding and I see many gardeners fail at this. The grass seed needs to be kept moist with frequent light watering, one to three times per day, until they germinate in approximately two weeks. Letting them dry out during this time can dramatically reduce the germination of the seed. A light layer of compost can help retain moisture for the seed.

For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.