Q. I have fifteen-year-old, 20 to 30 foot pines on a half-acre. They suffered during the heat this past summer. After your advice, I am doubling the amount of water and hosing off the needles once a week. How long is the recovery time using vitamins?
A. I am not a big fan of applying vitamins like Super Thrive. Some people swear by them, It can be cheap insurance though if you're not sure. Your call on that one.
Washing the needles of pines is not necessary. It is true of Italian cypress because they tend to get spider mites. Pines do not.
They might need more water than 15 gallons. Play that by ear by watching the new growth next spring and early summer. You should get at least 12 inches of new growth every year and not experience severe needle drop during the hot months. Those are indicators the tree is not getting enough water.
Once you find the right amount of water (minutes and gallons), keep it consistent through the year. The amount of water they are given should not change much throughout the year. It's like filling a gas tank. Instead, change how often they receive the water. Summer months water more often. Winter months, water less often.
As plants get bigger, they require more applied water, not watering more often. Watering frequently with small amounts of water produces shallow roots and trees that blow over in strong winds.You should see an improvement in the first half of next year. Nothing this year.