Question and Answer – January 2008

In trying to help almost all who have written, I have given short answers to most of the many questions that came to us.  We appreciate your notes, and I hope you find the answers useful. Again, it really helps when you send photos, also when you identify where you live.  I use the questions of greatest general reader interest.  Usually I do not include plant ID questions since they are of concern to only one person. 

Click here to send us your question.

Question:  Do you cut back crape myrtles?  If so, when?  S.W., no city given.

Answer:  Absolutely NOT!  Topping crape myrtles makes no sense, yet thousands of Texans persist in doing it annually. It ruins their natural shape forever, and it delays flowering the following summer. Research done by Dr. Gary Knox at the University of Florida has shown that removing anything from the tops of crape myrtles (even including seed heads during the summer) slows or prevents successive flowering.

Question:  We have old pecan trees on a farm and this year we’ve seen more limbs broken and fallen.  Some have told us it’s because of the spring rains and the heavy crop of pecans, while others have told us there is a disease attacking old pecans.  What can we do about it?  P.D., Anna.

Answer:  This is solely due to the heavy weight of the large pecan crop and the size of the individual pecans.  Pecan wood is brittle, so you do need to prune your trees carefully to avoid this kind of damage.  You also must remove all broken stubs that are present now. This is not due to any type of disease.

Question:  We need to move some very mature hydrangeas.  When and how should we do it?  L.F., Longview.

Answer:  Move them in late winter, specifically in February.  Maintain soil balls around their roots. You probably will have to prune them somewhat to compensate for roots that are lost in the digging, and that in turn will lessen or eliminate this year’s flowering.  But, the plants should be fine.

Question:  Oxalis has escaped a bed border and is growing in my lawn. I’ve used a weed-and-feed to no avail.  What will eliminate it without harming my St. Augustine or my trees’ roots?  D.C., Arlington.

Answer:  Many weed-and-feed products contain pre-emergent herbicides. They would have absolutely no effect on oxalis, yet they could do serious harm to your trees. I am a staunch non-advocate of any type of weed-and-feed products.  These two procedures need to be handled separately.  As to the control, if it were my landscape I would apply a broadleafed weedkiller by hand and specifically to the oxalis at its prime growth time in late winter.  Put one or two drops of a liquid dishwashing detergent in the spray to help it hold onto the waxy leaves of the perennial.

Question: My red oak leaves fell early this fall.  I noticed the same thing with others’ trees nearby.  Is there an underlying problem, or was the tree man correct when he told me it was the result of this spring’s rains?  C., no city given.

Answer:  It was due to the rains.  We saw a lot of fungal involvement on many of our plants, all due to the prolonged high humidity.  Next year will be better if the weather returns to more normal Texas conditions.

Question:  I applied Image in September and October to no avail with my nutsedge.  Is it ever too late to treat nutsedge?  H.R., Azle.

Answer:  Image must be taken into the nutsedge plants through their roots. Nutsedge is a perennial weed not unlike our perennial flowers – it dies to the ground each winter and returns in the spring.  Its activity slows after mid-September, hence the reason to wait. Treatment time is between mid-May and mid-September.  It works very effectively then.

Question:  When should Encore azaleas be fertilized and with what?  Since they bloom all along, it would seem that a modification from the feeding schedule for their normal kin would be in order.  W. Arlington.

Answer:  Stick with the normal feeding schedule for azaleas.  That calls for a high-nitrogen (or all-nitrogen) fertilizer immediately after the prime spring bloom and again 8-10 weeks later.  In early September apply a specialty azalea-camellia food.

Question:  I’ve had a lot of weeds in my buffalograss lawn.  What kind of weedkiller should I use?  Should I cut back on the watering in the winter?   S.V., Mineral Wells.

Answer:  You can use a broadleafed weedkiller to eliminate clover, dandelions, henbit and other broadleafed (non-grassy) weeds in buffalograss.   There is, however, no way to eliminate existing  grasses without doing damage to the buffalograss itself.  If you have grassy weeds, hopefully they are annual types that could be eliminated with a pre-emergent herbicide applied before they sprout next time around.

Question:  What type of evergreen shrubs stay at less than 3 feet tall and also produce berries?  The bed gets morning sun and shade in the afternoon.  J. and L. S., McKinney.

Answer:  Dwarf Burford holly would be your solution.  No other dwarf shrub is both evergreen and a reliable berry producer under those lighting conditions.  However, do look into other good evergreen shrubs. You can always provide feeders for the birds.

Question:  I have a silver maple tree which my son grew from a seed.  It is about 35 feet tall and 17 years old.  Will I hurt the tree if I fill the two octagonal rings 5 inches deep with soil for groundcover plantings?  R.M., Commerce.

Answer:  You could.  It’s not a good idea to add to the level of the soil beneath trees.  However, you asked for my opinion and I’m going to expand it even further.  I would put in a larger groundcover bed, and I would use metal edging driven almost totally into the soil so that the new bed could be at grade level.  You don’t gain anything by raising the bed those 5 inches.  I would also use an irregularly  curved boundary to my bed, and I would want the trunk to be off-center.  That way you’re not drawing so much attention to the tree’s least attractive asset – its trunk.  I equate it to a man in a tuxedo wearing white sneakers.  But, that’s just one guy’s opinion.

Question:  Why would three 2-year-old Carolina jessamine plants be turning yellow?  Some of the roots were exposed for a good while, but I have covered them with compost now.  J., Lewisville.

Answer:  Carolina jessamine, like roses and azaleas, are almost evergreen.  Probably one-third of their leaves will yellow and fall late each autumn. That would be the more likely cause of the yellowing, but it could also be from stress from the root exposure.

Question:  I stuck an avocado seed in a pot and now it has grown. Will it ever produce fruit?  How much cold can it stand?  L., Washington County.

Answer:  It can’t stand the amount of cold you have in the Brenham area.  It dies at 32 F.  Keep it in the pot as a novelty foliage plant.  Pinch out its growing tip to keep it more compact, and enjoy it as long as you can.  It will eventually have to be discarded and replaced with a new seedling.  If it did produce, it would not be the same as the mother avocado.  Just as a general rule, you should never start any fruit crop by planting seeds if you expect it to produce.

Question:  Can I grow Japanese maples in my shallow, alkaline soils?  C., Midlothian.

Answer:  You need to excavate and give each tree a 6- to 8-foot planting area consisting of 18 inches of highly organic landscaping mix.  They would yellow in your alkaline, chalky soil.  However, given the better soil and shade almost all of the day, they should really do very well.

Question:  We have two mature cypress trees approximately 30 feet from our house.  Will the knees do damage to the foundation?  I’m finding them coming up in my beds.  P.T., Tyler.

Answer:  They probably won’t do damage, but they are certainly annoying.  Dig a trench outside your beds and install a root barrier to stop their spread.  Your nurseryman will have the barrier.

Posted by Neil Sperry
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