Question
Hi Jim,

About 5 or 6 years ago, I purchased 3 large, mature, Douglas Firs, and had them professionally planted. They are approximately 20-25 feet high, about 4-6 feet in diameter at the base, and the trunk is about 4-6 inches in diameter. They are 8-10 feet apart, in line. They get about half sun and half shade.

This year, although they have never looked great, they began to show a lot of 'yellowing' or 'browning', mostly at the lower half. The upper half shows mostly green and even a little new growth. I believe that they need acid. Last week, I used Miracle-Grow for acid-loving plants, and following directions, I mixed 1 tablespoon for each gallon of water, and sprayed on  about 4 gallons of the mixture, half on the leaves, and half on the ground or 'drip-line'. I repeated this procedure for each of the 3 trees, using 4 gallons for each tree.

This is a little late to ask, but was this correct? How should I modify this procedure, and how often should I repeat it?

Any help that you can offer will be greatly appreciated.

Thank you, and Regards, Ken.

Answer
Conifers  prefer well-drained soils with a neutral to slightly acid pH. And maybe your soil is acid now, a soil test would need to be made to determine this. The tree nursery should be able to help on how to obtain a soil test. The miracle-grow is ok but I would suggest using Holly-Tone instead next time.

In the case of all conifers, it's best to fertilize at the end of April, and a second time in the fall, on first of August and only use acidic Holly- Tone. fertilizer, granular, time-released, evenly-balanced fertilizer. Unlike Mir- Acid. which is a high-nitrogen, constantly-applied fertilizer, Holly-Tone shows results gradually and doesn't dose the plant with too much, all-at-once. Mir-Acid requires repeated applications, "jump-starting" and "crashing" the plant constantly. Holly-Tone is much gentler with a more even feed.

The most important thing for a new transplanted tree especially one this large is water. I would suggest during dry weather you water the trees. A tree needs about 1 inch of water per week. The best way to measure this is put a pan under the tree and turn the sprinkler on and when the pan has 1 inch of water in it stop. Do this once a week unless it has rained. I would suggest that you may want to consider mulching around the tree to help hold the moisture. Pine straw would be great since it also provides some acid. If you use something besides straw do not pile it up on the tree trunk and limit the depth to about 4 inches of mulch.

After a couple of years and if the soil test show the soil has a pH that is  neutral to slightly acid I would change to a complete fertilizer such as 10-10-10. Conifers do not need a great deal of fertilizer unless the soil is poor.