Question and Answer – April 2008

There were dozens of questions this month.  I’ve decided to tackle those we have not answered in the past couple of months.  If yours is not addressed below, please check our MAQ pages on our website.

Click here to send me your question for our next e-gardens (questions with photos take priority).

Question:  I have an oakleaf hydrangea growing fairly close to my house.  The attached photo, taken several weeks ago, shows its form.  Should I prune it?  If so, when and how much?  Should I just move it?  If so, when?  V.O., Chandler.

Answer:  Oakleaf hydrangeas are great shrubs (much more landscape-friendly than their florist counterparts).  Wish we had gotten this before the last e-gardens, but you can still prune it gently to get it to regrow.  In the long run, you probably should consider moving it farther out from your house.  That’s a winter job, and you should probably spend the balance of this growing season root-pruning it to minimize the shock when you do move it.  Use a sharpshooter spade to cut its lateral roots 12 to 15 inches out from the trunk in all directions.  New roots will form and help hold the soil ball when it’s transplanted.

Question: I would like to plant a shrub that will grow to 10-15 feet tall as a privacy screen. I know not to plant red tip photinia any more due to its propensity for disease. Please give me a suggestion for the best, fastest growing, most disease-free shrub.  C.S., Granbury.

Answer: In alkaline soils like you have, you could use any of several tall hollies (yaupon allowed to grow shrub-form, Nellie R. Stevens or Mary Nell).  Of the three, you’ll be able to find Nellie R. Stevens in larger sizes.  You could also use Japanese ligustrum or the old-fashioned Chinese photinia, although neither is commonly sold in nurseries.  Chinese photinia, as a side issue, seems to be virtually immune to the Entomosporium fungal leaf spot you referred to.  Readers seeking a taller screen might consider eastern redcedar junipers.  They’re native over most of the eastern half of Texas. They grow to 30 feet tall and 25 feet wide.

Question: When do you prune fig trees, and what type fertilizer would be best for them?   C.B. no city given.

Answer: You’re in luck.  You really shouldn’t prune figs much at all (only to repair damage or to remove erratic branching), and they should not be fertilized.  They also do not require spraying.  They are low-maintenance fruiting plants to be sure.

Question:  We have two low planter boxes along each side of the front of our house.   Dwarf yaupon hollies beneath a live oak tree don’t look very good, but those on the sunny side are thriving.  My husband wants to prune the live oak more, but I think the overhang of the house causes too much additional shade anyway.  What kind of small shrubs would work well on both sides?  J., no city given.

Answer:  Planter boxes like that were the worst thing that ever happened to home landscaping.  They are ultimately limiting from a landscape design standpoint. I would definitely not prune the live oak.  It’s a far more valuable landscaping asset than shrubs ever could be.  I also would not feel compelled to do a mirror-image landscape to match the two sides.  Consider a shade-tolerant tall groundcover such as liriope.  You didn’t tell me where you live, so I can’t give a specific answer, but South Texans could consider evergreen ferns such as holly ferns, or cast iron plant (aspidistra).  You could use a trailing groundcover such as English ivy or Asian jasmine and keep it trimmed neatly.

Question: Some of my Nana nandinas have leaves which are very yellow.  What type of fertilizer should I use?  What causes the lower leaves of the bush to drop off?  J.J., Dallas.

Answer: Of all the nandinas we use here in Texas, Nanas are the ones that commonly face issues.  You may be seeing iron deficiency, in which case adding an iron/sulfur material in combination with an all-nitrogen lawn food might help.  Nanas also struggle with heavy clay soils during periods of extreme rainfall or drought.  Your plants have seen both in recent summers.  If you ever decide to replace them, consider Harbour Dwarf nandinas. They grow to the same height, but they’re much more dependable. They look more like a standard nandina.  Winter color is a rich maroon.

Question: How can I store tulip bulbs. Do I let them die back like daffodils and then dig up, dry out and store in fridge? A.V.,  Bedford.

Answer: Tulips are treated as annuals in Texas.  The only rare exceptions would be the comparatively uncommon group known as "botanical" tulips. They have smaller buds and flowers, often several per bulb. They naturalize and rebloom dependably, where the hybrid types never will.  Either way, leave them in the ground.

Question: My liriope keeps dying with no visible signs of disease or insects. I’ve been told it is a soil or root problem. Can you point me in the right direction? T.W., no city given.

Answer:  I have had the same problem with a couple of my own beds of Silvery Sunproof liriope.  It developed a bad fungal leaf spot over the winter and spring and died away.  I was able to slow the disease with a drench and spray of a general-purpose fungicide, but I grew tired of the responsibility and changed the bed out to mondograss.  Even though it’s related to liriope, it has shown absolutely no signs of the problem in the 10 or 15 years that it’s been in that location.

Question: Is putting pine straw mulch next to a frame building a danger because of termites? D.O., Jefferson.

Answer:  No.  Pine needles are fairly slow to decay, plus they’re not as attractive to termites as larger chunks of hardwood limbs and roots.  Termites are native anyway, so you don’t have to worry about attracting  them. They’re already there.  Work with your local pest control specialists to monitor their presence. That’s either with or without the mulch.

Question:  We have a lovely 30-year-old weeping willow tree in a low, wet spot in our yard.  I’d like to put a French drain in to remove the standing water. Does the willow depend on it?  I don’t want to risk losing it.  E., Flower Mound.

Answer:  You’re not going to believe my first comment, but weeping willows in most of Texas have an average life expectancy of 5 to 10 years.  They are highly susceptible to cottonwood borers, and, to a lesser extent, to cotton root rot. I have noticed that trees that line ponds seem to live longer, so, to that degree the standing water probably does help the tree.  However, as much as you like it, you shouldn’t let a willow dictate how you live and how you design the rest of your landscape. Consult with an arborist on-site, then hire a skilled landscape contractor to install the French drain if you decide to go that direction.

Question: I plan to plant four varieties of peppers this year.  I have read that different varieties can cross pollinate.  How far apart do the different varieties need to be to keep my sweet banana peppers from being hot as jalapenos?  N.K., Hurst.

Answer: Plant them side-by-side.  If they were to cross-pollinate, the results wouldn’t be noticed until you planted the seed and grew your next crop.  Think about it from the Animal Kingdom. Dalmations don’t look like golden retrievers just because they pair up.  Their offspring, however, can take on the properties of either parent (or, more likely, a combination of both). In a loose comparison, things work the same way with plants.

Question: I have a double rose of sharon shrub that is now 3 years old. It sets lots of buds, but many of them fall off without opening. What can I use to stop that?  I.S., Waxahachie.

Answer:  That is, sadly, a very normal occurrence for rose of sharon.  The plants set their buds in late spring. Temperatures and humidities are perfect for them at that time. But, by the time the buds start showing color and the flowers start opening, conditions turn much less favorable (hot and dry).  What you’re seeing is a natural aborting of anywhere from one-third to two-thirds of the buds. I’ve watched it happen to almost every other althaea I’ve been around in Texas, my own included.  The only year when they seemed to open much more normally was last year, and it was due to the ongoing rain and cooler weather.  Good luck. Sorry I don’t have a more positive answer.

Question:  My mom bought a small fir tree for Christmas.  It was doing fine for a while, but then it started to turn yellow.  I think it was way too wet.  I replanted it into a better pot and soil that did not stay so wet.  How can I save it?  S.B., Tyler.

Answer: Many types of small evergreens are sold as tabletop Christmas trees each December.  Unfortunately, most of them are not adapted to the Texas climate.  Like the roses of sharon mentioned just above, it’s hotter and drier for them here in Texas than they would choose.  It would help to know specifically what type of tree it is, but your best bet will be to do exactly what you have done.  Give it full sun the rest of the spring and in the fall, but afternoon shade during the summer.

Question: Our wisteria produced hundreds of seeds last fall. We could hear the pods cracking open and dropping the seeds. Small plants are showing up now all through our flower beds. Will they be the same as the mother plant?  K.B., Alvarado.

Answer:  Probably so, but there is so much agony from gardeners who swear they have wisterias that are poor, non-flowering selections that I would never recommend using the seedlings as the means of getting new plants. They are too easy to root from cuttings or via tip layers. That way, you’re sure you’re getting the same plant as mama.

Question: My irises have turned all white. What should I have fed them?  K., no city given.

Answer:  The old-fashioned white flags are extremely vigorous. They got mixed into your bed and have overtaken the others.  It is not a matter of nutrition.  Start a new bed of improved varieties this fall.

Question: My Knockout roses started dropping leaves in their centers late last summer.  The plants are very lanky and unattractive.  Does this look like black spot (photo attached)? What should I do?  S., Waxahachie.

Answer: Even our most durable roses (including Knockout) suffered during the prolonged wet weather last summer.  Black spot invaded plants that normally are resistant.  Roses are also semi-evergreen in the northern half of Texas. Those two things combined probably left you with this issue.  Thin out the dead wood, and try to prune to keep the plants compact.  It would have been better had you done this pruning 6 weeks ago. You’ll have to compromise a bit on the extent of pruning you do at this time.

Question: I moved into my home at the end of August. The previous owners had the lawn nicely landscaped. On either side of the driveway are creeping juniper plants. On one side the juniper is a nice, deep green. The other side started turning yellowish (not brown). My driveway faces the north. Someone told me it might be root rot. Is there anything I can do to save the juniper? E.G., Fort Worth.

Answer: I have two completely diverse answers.  Neither is guaranteed, but I have seen both.  The less likely one:  you may have two different varieties.  The trailing juniper Andorra turns maroon over the winter, then back to dark green during the growing season. I have it at my house, and actually it wasn’t especially attractive this winter just completed.  I remember the entry to the Vet Medicine School at A&M when I was a young horticulturist growing up in College Station.  They had planted Tam junipers on one side of the walk and Andorra on the other.  They looked fine all summer, but winter was a different story.  Very mismatched.  And, then, the other option:  spider mites.  The species that attacks trailing junipers is very active in February and March. Affected plants turn an insipid green, then yellow, then tan.  You can see the mites if you thump one of the affected twigs over a sheet of white paper.  They’ll be almost microscopic.  If you see them, spray the plants soon with a general-purpose insecticide.  Spider mites can be fatal to junipers.

Question:  What is the difference between 2,4-d and MSMA?  Are they interchangeable?  R.R., Sunnyvale.

Answer:  They are as different as clover and crabgrass.  2,4-d is a broadleafed weedkiller.  It attacks non-grassy plants such as clover, dandelions, henbit, chickweed, dichondra, thistles, dollarweed and poison ivy without harming turfgrasses.  MSMA is a grassy weedkiller.  It can only be used in bermudagrass lawns, and its function is to kill crabgrass, grassburs, dallisgrass and even invading St. Augustine without harming the bermuda.

Question:  How are nandinas propagated?  Are they grown from the berries, stem cuttings, or how?  I love their non-fussy nature and want a long row of them.  K. Dallas.

Answer:  The old-fashioned standard nandina, occasionally known by its common name "heavenly bamboo," can be grown either from its seeds or by dividing established plants over the winter.  Home gardeners will propagate the other varieties by dividing the old plants.  Nandina spreads slowly by sending up new shoots next to the mother plant.  Those are the shoots you can most easily dig and divide.  It works best with types that clump and spread most freely, including ‘Compacta’ and ‘Harbour Dwarf.’  Many of the other types are actually started as horticultural clones in professional tissue culture laboratories.

Posted by Neil Sperry
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