Garden Talk

with Rebecca Jordi


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Q: I am just not successful growing butterfly bush along the coast here. What am I doing wrong?

Butterfly Bush

Butterfly Bush

A:   You are doing nothing wrong it just butterfly bush (Buddleia spp) prefers a more inland climate, especially in our sandy soil. They do not like high humidity and watering them twice weekly should be avoided.  They can develop mildew problems on their leaves if they are not getting good air circulation. Well-drained organic soil is the best.  Of course, we do not want you to use any type of pesticides around the shrub as it can kill the butterfly population which should be one of the reasons for growing the butterfly bush. We planted Buddleia Lo and Behold ‘Blue Chip’, which is a trade-marked plant. We have had incredible success with it. This butterfly bush dies back in the winter but returns each year.  It is a dwarf variety and so pretty. 


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Q: My gardenia is not doing well and I am thinking the soil pH might be the problem. How can I get it tested?

Gardenia Flower

Gardenia Flower

A:  Go about 6-8 inches deep and take several samples from around the root area placing the samples in a bucket.  Mix the soil and bring us one sample – about a cup is fine.  Master Gardeners man the Yulee satellite office on Fridays 10am – 2pm and can run a pH for you at no cost.  Call us at 904 530-6351 for directions to the Yulee satellite office.  You can also drop the sample through the letter box on the door and we can run it anytime during the week.

Now, just a few things other things to consider regarding your gardenia shrub:
1.  Gardenias should not be planted by the foundation of a home or near the sidewalk, driveway, or walkways as these concrete structures leach and have a tendency to raise the pH to uncomfortable levels for these acid loving plants.
2.  Planting them under the eaves of the house encourages leaching too and often the plant will get too much water off the roof if there are not gutters.  Too much water can create the prefect environment for disease such as fungal leaf spots and root decays.
3.  Some cultivars of gardenia do better with morning sun exposure and afternoon shade.
4.  Keep lawn grass as far away from any tree or shrub as the things we do to lawn grass we should not do to trees or shrubs.  Be careful about applying lawn grass weed killers around the roots of trees or shrubs.
5.  Keep mulch off the trunk or any tree or shrub.  Allow for an area around the base of the trunk which contains only soil and air.  Mulch should be only 2-3 inches deep.  Never use rock as it can compact the soil and retains heat – neither is good for trees or shrubs.  Pine products are preferred.
6.  It is critical to ensure the shrub is not planted too deeply.  You should be able to find the large roots coming off the trunk in just an inch or so of soil.  More than a few inches of soil on the roots is too deep.
7.  Watering the shrub twice a week like the lawns can be excessive and they hate it.


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Q: The buds of my hibiscus are turning yellow and dropping off. What is wrong?

Hibiscus bud midge maggot

Hibiscus bud midge maggot

A:  After opening one of the yellowing buds we discovered the hibiscus bud midge maggot, Contarinia maculipennis.  The female midge deposits eggs on the tips of the newly forming buds and within 24 hours the maggot develops and starts to feed on the bud.  It takes about one week for the insect to mature to the next stage; then they drop to the ground to pupate. The soil must be moist, which is generally not a problem in our landscapes.  It will take about 2 -3 weeks to mature into an adult. The adult midge is very small – similar to a mosquito. Although hibiscus is the favorite, the bud midge has been known to also infest tomatoes, jasmine, plumeria, other vegetables and ornamentals. There are other reasons for flower buds to turn yellow and drop off such as over watering, too much nitrogen, thrips or aphids, and very hot, dry weather.  However, since I found the maggot, I am going to blame it on the bud midge.  The best thing for homeowners to do is to be sure to clean up any buds and leaf litter which have dropped to the ground.  If the hibiscus plants are in the ground they may not need supplemental watering aside from what we get with rain.  Remember, the midge requires moist soil to pupate.  Contact chemical sprays don’t work well since they cannot penetrate the bud.


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Q: What is the name of this plant and what can you tell me about it?

Japanese serissa

Japanese serissa

A:   I was glad you were able to show me a close-up photo of this plant.  Although it took me a little while to remember it, I finally realized the shrub was Japanese serissa or Yellow rim, Serissa foetida.  It can be grown in cold hardiness zones 7-9, which means anywhere in Nassau County, Florida.  Generally, it is classified as a semi-evergreen with small white flowers appearing in the spring.  Sadly, the flowers have no fragrance. The small green leaves have a thin outline of yellow – which is where it gets the common name Yellow rim.  It can be grown in most any type of well-drained soil in full sun to partial shade.  It would be considered a dwarf shrub as it reaches heights of only 3-4 feet with the same size spread.  However, it has a tendency to sucker similar to yaupon holly.  This means you may need to occasionally clip it at the bottom to keep the suckers in check.  It truly has no serious insect or disease issues if NOT over-fertilized or over-watered. This means it should not be in the pathway of any irrigation system.  Once it is established – usually just a few months – it is practically care-free.  Japanese serissa shrubs make a nice backdrop for perennials such as African iris, coneflower or yellow bulbine.  We will have a few of these shrubs at the spring sale on Saturday, May 7 from 9am to noon at the James S. Page Governmental Complex.  Remember these plant sale funds are used to provide us with professional development and help us maintain the two demonstration gardens.  Please come out and support us – see you there. 


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Q: What can you tell me about cape honeysuckle?

 Tecoma capensis

Tecoma capensis

A:  Cape honeysuckle, Tecoma capensis, originates from the Cape of Good Hope region of South Africa.  This plant might be a little tender here as it prefers cold hardiness zones 9b – 11.  Remember, Nassau County Florida is generally classified as being in zones 8b – 9a.  This means, if we get typically cold temperatures in the winter – this plant might not survive. Cape honeysuckle shrub puts out a cluster of deep orange flowers in the spring through the fall. Treat as vine with support but it can be pruned into shrub form. This plant can attract hummingbirds and butterflies. The cultivar, ‘Apricot’ is smaller and more compact with orange flowers. ‘Aurea’ has yellow flowers.  You might consider planting a trumpet vine, Campsis radicans, instead of the cape honeysuckle as trumpet vine plant can be grown in zones 4b -10a. Trumpet vine is also a Florida native and it also attracts hummingbirds. Like many vines, trumpet vine flowers best in a full sun location. It grows but flowers poorly in a shaded location. It will do fine in any soil except those kept continually wet and flooded.There are several cultivars: ‘Atropurpurea’ – large, dark red flowers; ‘Speciosa’ – bushy growth habit; ‘Flava’ – yellow flowers; ‘Praecox’ – blooms earlier.


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Q: My boxwoods are dying. What might be causing this?

Boxwood

Boxwood

 

A:  This could be an indication of root decay but there are fungal pathogens which can also cause limb dieback. If possible, consider bringing me a clipping so I can better determine what might be the real problem. Limb dieback can be caused by over-watering, heavy mulching and over pruning. There are no chemical recommendations for this – just cultural changes:

 

 

  1. Boxwood plants are drought tolerant plants – consider removing or capping the irrigation. Watering twice a week can cause some serious issues.
  2. Mulch should not be touching the trunk of any tree or shrub and should be only 2 – 3 inches thick.  Over time, mulch layers can build up and contribute to root problems.  Heavy mulching should be removed.  There should be an area directly around the trunk with nothing but soil and air.
  3. Consider allowing the shrubs to reach a slightly higher height to avoid over-pruning.


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Q: Should I prune my gardenias or azaleas now?

Gardenia

Gardenia

A:  This is one of the most common questions I get every February.  So I am repeating my answer from a previous Garden Talk.  Gardenias, like azaleas, would need to be pruned after they have finished flowering, which will be sometime late spring or early summer. The best management practice for most any flowering plant is to prune directly after flowering. If they are pruned now in late winter, then we will reduce the number of flowers produce as the buds for flowering have already been formed. Gardenias and azaleas really require very little pruning except to improve their shape and/or remove broken or diseased stems. It is possible to prune azaleas or gardenias to increase flower production but keep the removal of stems to a minimum. Selectively prune a stem by hand rather than use a motorized pruning utensil. Hand prune the stems selectively by cutting back to a bud and be sure the stems are cut at a proper angle. Cuts should be made about ¼ inch above the bud. It is also best to prune the shrubs so they are smaller on the top and larger on the bottom to allow for the best exposure to sunlight. Remember, gardenias like well-drained, acid, organic soils. It is important not to water them as often as we do lawns. Avoid using heavy rock mulch around the root area as this will cause compacted soil. Consider using pine straw or pine bark as a mulch. Leave an area about 12-18 inches around the trunk with nothing but soil and air, which is an excellent practice for any tree or shrub.  I know everyone is eager to get out and prune their perennials but it is best to wait a little longer until we are certain the fear of freezing temperatures is truly over.