Iron deficiency in pin oak

Iron deficiency in a pin oak, such as in the picture, is possible but not a true Shumard red oak.

Q. Dear Neil: I was given a blueberry plant this spring. I’ve been growing it in a pot with potting mix and fertilizing it regularly. It was doing well until June, but now the leaves are turning brown and falling off. I had it outside, but now I have brought it indoors. What is causing it to turn brown, and what can I do now?

A. The browned leaf edges indicate some type of moisture stress. It’s possible that it got too dry one or more times, but it’s also possible that there has been a buildup of mineral salts in the soil. That actually is what it looks like. You need to leach the soil thoroughly by flushing it with a great deal of water and letting the water drain out completely. Honestly, this plant needs to be set into highly acidic soil outdoors immediately. Blueberries are adapted to East Texas. Elsewhere, they would have to be grown in highly amended soils that consist of 100 percent organic matter. You also need a second variety that blooms at the same time to ensure good cross-pollination. To be candid, blueberries are hard to justify financially when you get outside their prime East Texas area of adaptation. It’s better just to buy the fruit in the grocery.

Q. Dear Neil: We planted three wisteria plants on a pergola last year in an effort to create summer shade. They have grown very well at the top, and we have been able to control them there. However, at the bottom, we have had many runners that have made it difficult to walk. What time of year can we prune them, and how can we tell what should be removed?

A. That kind of pruning can be done at any time of the year. You’re really not expecting flowers on those bottom shoots, so timing doesn’t matter. When you remove each of the branches, cut it flush with the remaining trunk. I don’t know if you’re aware, but wisterias are huge vines. It’s not unusual for them to grow 40 or 50 feet long. Hopefully your pergola is very strong. The best rule of thumb is to remove any stem that is growing where you don’t want it.

Q. Dear Neil: I am reading your column from Georgia. When is the latest I can plant purpleheart (Setcreasea) into the ground and not have to worry about it freezing?

A. Georgia varies a lot from north to south, but as a general rule I’d try to have them planted by the end June, preferably earlier. Use shredded leaves over their crowns in the winter. Apply them after the first killing freeze to gain 8 or 10 degrees of protection.

Q. Dear Neil: I have two Chinese pistachio trees in my yard. One has had browning of its leaves the past two summers, while the other has remained good looking all the way through. They get the same amount of water, and I have not sprayed the trees with anything. It seems to be getting worse each year. What is wrong?

A. Without a photo I’m going to have to make some assumptions. I had the same thing happen to my Chinese pistachio many years ago. It was about five years old, and its leaves started to brown by July. We actually sold the house and moved, but when I drove by a few years later, the tree was doing fine. That was later in the summer. I finally figured that it was growing fast enough that it just couldn’t keep up with its moisture needs. Unless you are seeing some kind of trunk or root damage, that’s about all I have to offer. It might be worth having a certified arborist in for an inspection.

Q. Dear Neil: We planted our red oak nine years ago. It is always looked healthy until late last summer. This spring it came out with lots of yellow leaves, and now some of the branches are already bare. They are light green in color, which sounds like iron deficiency. But the leaves are developing brown spots. What is the problem and what corrections can I take?

A. You identified your problem correctly. This is iron deficiency. Normally, a Shumard red oak would not have this problem, but you do not have a Shumard red oak. You have some other kind of oak, perhaps a hybrid oak with pin oak genes involved. Pin oak (Quercus palustris) leaves look very much like those of Shumard red oaks, but pin oaks must have acidic soils or they will eventually develop iron deficiency symptoms. It generally shows up after 10 to 12 years, once the trees grow out into alkaline soils. I could baby you along and suggest that you apply iron and a sulfur soil acidifier, which you are welcome to do. However, in the hundreds of times that I’ve seen people try that, I have never seen it work. The trees just get too big to be able to take in enough iron. It’s best to bite the bullet and replace it with another tree species. I might note that this most often happens with trees that have been bought from national chain stores. Local independent retail nurseries usually buy from Texas-based growers who know the difference.

Have a question you’d like Neil to consider? Mail it to him in care of this newspaper or email him at mailbag@sperrygardens.com. Neil regrets that he cannot reply to questions individually.

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