Summer Watering Tips for Portland Area Landscapes
First Rule…Do No Harm. If you are watering every day, this is harmful and as far as you can get from the ideal watering practice for your plants’ health and for growing in your design. Plus you will be accidentally training your plants to be shallow rooted and water hogs. One is not good for the plants and the other not good for your wallet. If this is how you have been watering for years and you want to change, let’s talk.
Watering First Year Plants
I consider any plants that have not been through a summer to be a first year plant. I typically have clients start watering first year plants every 2 weeks in April (depending on weather conditions in the Pacific Northwest). This can continue into the mild temperatures of mid-May most years but by the end of May, the temps can go up dramatically. New plantings and first year plantings should be getting watered thoroughly twice a week in late spring. When we start having 85 to 90 degree weather, first year plants should be watered thoroughly 2 to 3 times a week maximum, not every day and not just a splash. We want to manage the plants heat stress with other methods besides watering.
Don’t wait until you see signs of stress to check the soil moisture with your hands – it can be hard to get moisture back into clay soils once they dry out. Do you see leaves wilting, scorching, crumpling, or dropping even though the soil is moist?
Here are Tips to Prevent or Minimize Heat Stressed Plants
(1) Sprinkle water on the leaves to cool them off in the evening when light is not on the leaves, or very early in the morning (before 8 am). Never sprinkle water on leaves after 9 a.m. in sunny weather, this will cause scorched and damage leaves and flowers.
(2) The Sheet Trick – Cover your plants’ leaves for up to 3 days. Covering plants helps them conserve water loss and deal with the shock of temperature change. When not exposed to the sun, the cells in the leaves will close. When closed, the leaf cells do not release water. Covering the leaves conserves the existing water in the roots and leaves.
To cover the plant take a lightweight fabric (a white or light colored sheet is ideal) and attach it to the plant during the most extreme heat. I like to use black office clips on individual trees or shrubs. Or use rocks to hold the fabric down if you are covering an entire bed. Note: This is also an excellent way to protect a plant from drought stress after transplanting new plants.
(3) In late summer when heat spikes up to 100 degrees you could add one additional watering per week. Check your soil a few inches down with your hand. If it’s still moist, watering is not the solution and may be the problem.
Watering Established Plant Material
Plants 2 or 3 years old are established plants. If you have heavy clay soil you may need to water twice a week even in early summer. Apply the water slow and for a long period of time. You do not want the clay to dry out. Its very difficult to get it to accept water after that. All plants will respond to sudden change in temperature, for instance mild early summer weather interrupted by 3 days of intense heat, you will see leaf droop or slight wilting regardless of whether the soil is moist or not. As soon as the intense heat retreats, the plants leaves return to normal typically. The only way you will know if they need additional watering over and above your typical practice is if you check the soil. Remember, too much moisture and too much heat equals root rot. Remember first rule, do no harm.
For more about protecting plants from heat see Hydrangea Love.