Adapted from information by Patrick Mawhinney, from his website Prestige Shrub, Tree and Turf
All trees, including Leyland Cypress, require at least 5 gallons of water per inch of trunk diameter applied one time per week. This means if you have a 6” diameter trunk on your tree, the tree needs 30 gallons of water applied one time per week.If you have a drip system with emitters then you should have 4 emitters per tree (one at the 12, 3 6, and 9 position) for uniform watering. Have your irrigation specialist tell you how much water the four emitters apply per hour so that you can determine how long to water to obtain the proper amount per watering.
If you use soaker hoses, make a 3'-4' loop around the base of each tree. Since soaker hoses are difficult to calibrate, water until you have moistened the soil to a depth of 6”-8” one time per week. Above 90 degrees you may have to add a second day of watering to maintain the soil moisture at the 6”-8” depth.
Leyland Cypress drought stress
Leyland Cypress is attacked by several fungal diseases. The worst of these diseases is Seiridium canker. Second in line of severity is Botryosphearia canker. These fungi cause cankering on the trunks and stems which eventually leads to the death of the tree. These diseases are much worse if the tree is in drought stress.
Though no chemical treatment is effective against these fungi, research indicates that if the trees are properly watered to eliminate drought stress, canker formation virtually ceases..
This is a prime example of how proper watering of your landscape not only maintains plant health, but is also directly related to disease suppression and prevention! Keep all your plants properly watered, especially your Leyland Cypress!
Leyland seiridium canker