Question and Answer – March 2008

Before I plow into this month’s many questions, let me apologize if I didn’t include the one you sent.  We had almost 50 questions.  I have spent about 5  hours working through them.  The 25 or more you see below are those I felt were of the greatest reader interest.  Due to the quantity of questions, my answers will be direct and to the point.

If your question is not included, it may be because we have just covered it within the past couple of months.  Several of those are in our MAQ in our website (neilsperry.com/maq/).  Please check there.

Also, several of you asked where you could buy certain products or plants.  Your best bet would be to ask a Texas Master Certified Nurseryman in your local area to help you.

To send your question please click here.

Question: I have two new magnolias.  How can I keep them thriving?  P., Haslett.

Answer: Magnolias need nitrogen fertilizer and ample water to grow at their fastest possible pace.  Sprinkler irrigation alone is not adequate for the first couple of years. Hand-water them to soak their soil deeply.  Apply a lawn-type fertilizer (no weedkiller included) in mid-March, mid-May and mid-September.

Question: We just purchased a 4-year-old house on a golf course.  I understand the underlying soil isn’t really soil at all, but white rock.   The lawn is sodded with common bermudagrass. What can I use to topdress the lawn to increase the organic material layer and improve the vigor of the lawn?  How often should I topdress it?  M.S., Benbrook.

Answer: Bermuda will grow very well without any of that "heroic" care.  Apply a high-nitrogen or all-nitrogen plant food to it on 8-week intervals starting April 1 and ending in early October.  Mow it comparatively short (1-1/2 inches), and mow it frequently (4- to 5-day intervals) to keep it low and spreading.

Question: My redtip photinias are looking terrible.  Someone told me there is a virus going around. Is there anything I can do to help my plants?  V.O., Garland.

Answer: Redtips are being ruined by Entomosporium fungal leaf spot.  Unfortunately, there is no good control for it, which is why few landscape contractors are using it any longer.  The short answer is that you might as well start figuring what type of shrub you’ll use to replace them.  Anything else would be wasting your time and money.

Question: I have gnats in the potting soil of my houseplants.  How can I get rid of them?  They are always there.  M.L.W., Crawford.

Answer: Those are called fungus gnats, and they indicate that the soil is staying consistently too wet.  They exist in the fungal mats that form on pot and soil surfaces.  Repot your plants into a perfectly draining potting soil in clean pots. Comb away the top surface of the existing soil balls.

Question: Please help me with a fully shaded back yard that is an ugly, muddy mess. What will grow beneath a big elm tree?  Bermuda seed last spring was a waste.  K.L.M., Garland.

Answer: St. Augustine (planted by solid-sodding) is our most shade-tolerant lawngrass, but even it will require at least 4 hours of direct sunlight daily. Unless the lower limbs of the tree can be removed to allow more sunlight early and late in the day, you’ll need to switch over to a shade-tolerant groundcover such as mondograss, liriope, Asian jasmine or purple wintercreeper euonymous.

Question: Can I save daffodil bulbs I ordered last fall?  I did not get them planted.  How do I store them?  J.W., Keller.

Answer: Bulbs are not like seeds, that is, they do not save for more than one dormant season.  Plant them immediately, and take your chances.  Give each a gentle squeeze. They may already be dried and beyond saving.

Question: We planted yellow columbines in our yard two years ago.  We have never pruned them, and now they are leggy.  Should they be pruned?  J.T., Abilene.

Answer: Columbines should be sheared back almost to the ground a month or two after they finish blooming.  By then, they should have gone to seed, plus spider mites usually take a toll on their old tops.  Established plants will often send out fresh, new growth as the season progresses.  Individual plants will live for a couple of seasons.

Question: My yaupon holly has gotten out of control height-wise.  Can it be pruned?  How much and when?  No name, no city.

Answer: So long as you are able to leave a good complement of foliage on the plant, it could be cut back by 25 to 35 percent.  However, standard yaupons will need to be allowed to grow to at least 8 or 10 feet tall and 7 or 8 feet wide.  They develop large trunks and keeping them shorter will not work in the long run.

Question: My small peach tree had lots of fruit last year, but they were only about 2 inches in diameter, and wasps and butterflies ate most of the crop. What can I do to prevent this this year?  J.McC., Roanoke.

Answer: You must thin peach and plum fruit to be 6 or 7 inches apart on the branches.  That will ensure that the remaining fruits reach full size.  The insects were probably feeding off sap that exuded from injury from plum curculios and other insects.  Follow the required fruit spray schedule from Texas A&M.  It is available online.

Question: My azaleas show no signs of setting buds, and they have brown spots on their leaves just like rose bushes.  What do I need to do for them?  B., Benbrook.

Answer: This one would require more information. Old azalea plantings in areas with alkaline soils and alkaline irrigation water go downhill and bloom becomes sparse.  The productive life expectancy of an azalea bed in the Metroplex probably averages 10 to 12 years. If your plants are old, this could all be due to iron deficiency.  If they are new, it may be nothing more than the normal yellowing and leaf drop that will occur each winter.  They need full morning sun to flower to best potential.  Do not prune them until after their blooming time has passed.

Question: I heard you mention that some vegetable crops should not be planted in succession.  My crops are usually squash, peppers, blackeye peas, green beans, cucumbers and tomatoes.  J.K., McKinney.

Answer: This crop rotation is to prevent a build-up of soil-borne insect and disease pests.  You should not plant the same (or closely related) crops in the same ground year-after-year.  The relatives you have given are tomatoes and peppers (nightshade family), blackeye peas and green beans (legumes) and cucumbers and squash (cucurbit, or melon, family).  Try not to plant those related plants in the same space in successive years.

Question: We have two groups of 20-year-old Pink Ruffles azaleas in our landscape.  One group is declining.  The plants’ leaves are thinning, and they are yellowing.  My husband mulches them every year and applies (brand name withheld by Neil) soil activator.  We need to replace some of them, but we’re concerned what the cause might be. We’d like to transplant the better group and replace them with Encore azaleas.  Suggestions?  D.A., Plano

Answer: This is the epitome of what I referred to in the earlier question. These azaleas are playing out. They’ve given you years more color than most of us in areas with alkaline soils get from our plants. Leave the better group in place. Moving them would weaken them so much that they wouldn’t be useful from this point on.  Replace the others with your new Encores, but prepare their soil carefully.  They need 18-inch-deep beds of equal amounts of Canadian peat moss and finely ground pine bark mulch.  They, too, will need 6 to 8 hours of full sunlight, preferably morning. The additive your husband used is of little value. Stick with conventional fertilizers, perhaps a specialty azalea/camellia food.

Question: What is the secret to getting onions to grow larger?  Ours are always about the size of ping pong balls. S.T., Mesquite.

Answer: Plant them in late January or early February so they can grow and develop during cooler weather.  Choose healthy, vigorous transplants.  Set them shallowly.  If you plant them correctly, as many as 10 percent should topple over and have to be replanted the first time that you water them.

Question: Would cottonwood rot kill St. Augustine?  Our lawn was beautiful for 40 years.  I tried the Canadian peat moss treatment last year.  It keeps fading away. No name, city given.

Answer: Cotton root rot is a soil-borne fungus that is responsible for driving cotton farmers out of the alkaline soils of much of Texas.  However, it does not attack any grasses.  Be sure your grass gets 4 to 6 (or more) hours of sunlight daily.  Otherwise, look through the several possible St. Augustine problems in our most-asked questions at our website.

Question: My 6-year-old plumeria continues to grow straight up.  It’s 4 feet tall and it’s in a 9-inch clay pot.  Should I cut it back? No name, city given.

Answer: Wow!  Thanks, for the photo. Wish more would supply them.  Yes, your plant needs to be trimmed back significantly (30 to 50 percent), then repotted into fresh potting soil in a 12-inch flower pot.  Put it in bright, indirect light outdoors once the danger of frost has passed.

Question: After two years of nurturing, my lime has started to bloom.  It’s in a large pot in a heated greenhouse.  However, its leaves are yellowing and falling.  What could the cause be?  D.K., Fort Worth.

Answer: Yellowing leaves indicate a plant that is not happy.  They are not very precise symptoms. I would be concerned about ventilation within the greenhouse if you use gas heat, also how much light it was receiving – they need full sunlight.  It could also have gotten too dry at one point, or it might have been exposed to a light frost at some point.  All would cause the yellowing.

Question: I have a bed beneath a large mulberry tree. The bed receives afternoon sun in the summertime.  What flower would give me a big assortment of colors?  What type of soil should I prepare?  R.B., Metroplex.

Answer: Impatiens and wax begonias give the best flower color in the shade.  Coleus and caladiums give good foliar color.  I hope I’ve pictured the amount of light correctly.  If there is a lot of afternoon sun in the summer, delete impatiens from that quartet.  Many of us opt, instead, for evergreen groundcovers, then use pots filled with the annuals for colorful accents at important spots.  Tropical plants with interesting foliage can provide textural interest as well.

Question: I have two very large pots on either side of my front door. They are completely shaded.  I’d like some type of evergreen in them. How would cast iron plants or hostas do there?  F., Cedar Creek Lake.

Answer: Cast iron plants won’t be winter-hardy enough for you, and hostas die to the ground for 5 months each winter.  Hollies are your best evergreen shrub options.  Consider dwarf yaupons if you want something small, to 3 feet tall and wide.  Dwarf burford holly grows to 4 to 5 feet tall and 3 to 4 feet wide. It produces large red berries each winter.

Question: How can I deal with cedar elm seedlings coming up in my beds?

Answer: You could apply a Gallery pre-emergent weedkiller, but only if you did not intend to sow seeds of any plants into the same soil that season.  A better way would be to put 2 to 3 inches of organic mulch such as compost or shredded bark over the beds. As the seeds germinated you could easily stir the mulch with a hoe or small rake and disturb the tiny seedlings so that they would dry out and die.

Question: When and by how much do I prune silver lace vine and Lady Banksia rose?  The rose has yet to attach to the fence.  L.T., Central Texas.

Answer: Silver lace vine is a rampant grower. Pruning won’t slow it down much.  Lady Banksia can be pruned after it blooms.  If you trim it now, you’ll be removing its buds as they begin to set.  By the way, it is a leaning plant and not a true vine. You must secure it to its support. It has no rooting appendages, nor does it twine around posts or wires.

Question: I have a 5-inch diameter live oak that is too close to a nearby Chinese pistachio tree.  The oak is now leaning.  The pistachio is my neighbor’s, and it’s the older tree.  Should I move the oak, or can I stake it to straighten it?  S.D., Denton.

Answer: You could hire someone to move the oak for you if it’s salvageable.  The crook in the trunk, however, will stay there.  You cannot stake the tree to pull it into plumb. It would immediately return to the angle as soon as you removed the stake, even years down the road.

Question: I have a very large palm tree in my landscape.  It has dead leaves hanging down from its top.  Do I need to remove these?  Will they eventually fall off?  They are far too high to reach without climbing. F., Lake Ray Hubbard.

Answer: This is strictly an aesthetic situation.  The palm will do just fine with the old leaves.  In urban areas rodents will often nest in the rubble. That’s one other reason they often are kept tidied up.  Specialized crews do this cleanup in areas where there are more palms.

Question: When is the best time to plant a new crape myrtle?  B.E., Keller.

Answer: If you don’t know exactly what variety you want, you probably should make your choice while they’re in full bloom the first half of this summer.  You’ll have to hand-water the plants every 3 to 5 days for the first summer to keep them from drying out.  If you know the variety you want, and if you can find it at a nursery, October is an ideal time to buy and plant.  Remember to ask how tall the variety grows.  Don’t choose a tall one if you have a small space.  We must never use pruning as a means of size control in crape myrtles.

Question: Do fire ants damage plants?  We have them in some of our shrubs, around their trunks.  M.D., Benchley.

Answer: Fire ants actually pulverize and aerate the soil.  Unless they form a mound up and over a plant, they present little danger.  However, you don’t really want them that close to your family and your home.  Use an area-wide bait treatment to eliminate them.

Question: What type of pine would grow in the Hill Country?  We have deep, fairly good soil.  Pinon pines are native about 100 miles away.  M.M., Kerrville.

Answer: Odds are, those pinon pines would probably do well.  Eldarica pines have also grown well in areas receiving 15 to 25 inches of rain per year, but plant on an elevated slope.  Many eldaricas were lost in the past couple of rainy springs.  Like many arid-area plants, they simply can’t cope with waterlogged soils.

Question: I love rhubarb desserts, but I can’t find any fresh or frozen rhubarb in stores.  Can I grow it here?  A.P., Wylie.

Answer: It’s too hot in Texas in both summer and winter for rhubarb to prosper.  Your grocer can order it in for you, at least in frozen packaging.

Question: Where are camellias best suited?  I have one growing in a pot and would like to set it out.  No name, no city.

Answer: If you’re talking about where in Texas, the southeastern quarter of the state would be ideal for them. They need acidic soils and Zone 8 winters.  Camellia sasanqua varieties are somewhat more winter-hardy, to Zone 7.  If you’re talking about where in your yard, they prefer morning sun and afternoon shade just like azaleas.

Question: When should I prune Silverado sage?  Mine is a little too tall and unshapely.  No name, no city.

Answer: Prune it immediately. Try not to remove more than 25 to 30 percent of its top growth.  Apply a high-nitrogen fertilizer to promote vigorous new shoots this spring. They will fill in the voids.