How to Rehabilitate Japanese Black Pine

Q. Are Black Pine, California Christmas Tree and Thumbergii all the same plant? I have 2 trees that are important in my landscape and have been doing well for several years. They were neglected recently so there is no place for deep watering and not fertilized in 2015. There is sap coming from the trunk. Should I try to rehabilitate them or replace them?

Japanese Black Pine

A. Japanese black pine is Pinus thunbergii so Thunbergii probably refers to Japanese black pine. I do not know if it is called California Christmas tree but I doubt it because Japanese black pine has a very unusual form making it a specimen plant in the landscape. It does not have the Christmas tree shape.

          Most of the textbooks say Japanese black pine tolerates alkaline soils but I have not really found them to be very tolerant of the hot desert and our soils. Many of them have been planted in Las Vegas but very few are still around which tells me many were removed.

          If you have Japanese black pine they are characteristically slow in growth and have a very distinguished form that adds character to a landscape. If you are looking for a Christmas tree pine this is not going to be it.

          They are slow-growing. If they have been neglected and do not look good they will rehabilitate very slowly. 

          Soil applied systemic insecticides that control borers would be a good if the trees actually have them. Pines can be “sappy” so make sure it is borers before you make the application. Wounding of the trunk and limbs can also cause them to bleed sap like borer damage.

          If you choose to rehabilitate them, put tree wells around the trunk about 2 feet in diameter to hold irrigation water. Give them a deep soaking with a hose once a month along with their normal irrigations.

          Fertilize them with 16–16–16 once a year in the early spring or apply it now if they haven't been fertilized this year. Punch some holes in the soil 2 to 4 feet from the trunk to a depth of eight or 10 inches. Put a handful of fertilizer in each of the holes and water them twice to activate the fertilizer and move it into the tree.

          Expect a very slow recovery if you choose to rehabilitate them. If they look bad now, I would suggest that you consider replacing them with something that you really like and can get instant gratification.