Determining Water Needs For Outdoor Flowers

(Question)

How does a person know how much to water outdoor plants? I have a variety, connected by soaker hoses in west Toronto, and don’t want to waste water or time.
I imagine it has to do with the individual needs of the plant, so maybe I should take an average of their needs.
Weather services aren’t trustworthy, so I tend to water on the same day, and keep records, but the duration of the soak is something I’m inquiring about. Peonies, roses and Irises are my concern, but hostas seem content with little water from experience.
I give the lawn one inch of water weekly, around the weather, using a measuring cup.

(Answer)

You are very methodical in your watering habits, and your plants will do well by that. Generally, the inch a week for the established lawn is sufficient, unless we’ve had a lot of rain, then you can back off the watering for that week.

Neither the irises nor the peonies need to be watered that often – these are well established perennials with large tubers that hold water well. Roses are a little more picky. If you have tea, floribunda or grandifloras, they could use  the more frequent watering, and preferably deeper watering, so the water reaches the roots. Sprinkling water just on the surface would not be sufficient.Roses that are closer to the wild state, such as the Explorer series, can withstand less watering, as they are hardier.

Continue monitoring the water availability in the soil. This is fairly simple; stick your finger into the soil and see how how far the moisture goes down into the soil. If it’s dry beyond your finger, it’s time to water. As for the hosta, they do need water as well, and the finger test works for them too. Although you didn’t say so, if you have hydrangeas, they are heavy water users, and will need more frequent, deep watering.

To help keep moisture in the soil, you can add approximately 10 to 15 cm of mulch around your beds, keeping the mulch away from the stems of the plants.

Many people plant up pots and baskets for the summer for that lovely hit of colour. These will need daily watering (unless there’s lots of rain), as the plants are confined to a small environment and tend to dry out very quickly.

If you are still unsure, there are many makes of moisture meters that can easily be stuck in the ground to test the moisture in the soil.