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Past Questions and Answers | March 2008

This month's questions concern:

Disturbing The Top Soil
Is Plant Acid Loving Or Not
Prune Rose of Sharon
Blossom-End Rot On Peppers
When To Prune Geraniums
Don't Prune Roses?
When To Prune Fruit Trees
Kill Poison Ivy
Fix Thinning Lawn
Using Growth Regulator On Hedge
Planting Caesalpinia ferrea

Please scroll down to read the answers.

Question #1:  Should I Disturb The Top Soil?

Question:  It was advised to me to make the soil loose on top of the container 3-4 inches (7-10 cm) inside every week. I am afraid I could hurt the roots doing so. If advised, then why it has to be done, although the soil used in pot is light weighted?

 Vihang Shende, Nagpur,Maharashtra, India


ANSWER:  Hi Vihang! This is a very good question. I personally would never disturb the top soil of a container plant that deeply. 3 to 4 inches (7-10 cm) is too deep, and as you mention, could do more damage to roots than would help.

Now - IF - you had a heavy soil like clay, that needed some aeration you could cultivate, or lightly loosen, the top 1/2 to 1 inch (1.2 - 2.5 cm) of soil once every few weeks, but never deeper than that.

The reason you would do it at all would be to provide more air circulation into a soil that has very small particles, like clay soil, and therefore does not provide good aeration for the roots.

Sounds like you are using regular potting mix, or at least a soil that has larger particles and perhaps has perlite, vermiculite or other materials that provide a nice, light airy soil, which plants love, and therefore you do not need to dig up or loosen the soil.

Follow your instincts, you are right on track!

Question #2:  Is Plant Acid Loving Or Not?

Question:  Is there a way to tell if a plant is acid loving or not ? Or do you just have to look up each plant?

 Denise Ducroix, Le Veurdre, France


ANSWER:  Hi Denise! Wouldn't it be great to be able tell just looking at them! Sure would save a lot time, but unfortunately you can't.

One thing you can do that will really help you is to look at the native climate the plants grow in. Most acid loving plants live in areas with high rainfall and soils high in organic matter. If you look at that native habitat of an azalea, camellia, pine, hydrangea, fern, or rhododendron, you will see that they all have soils with a pH of 5.0 to 6.0, which are very high in organic matter.

Plants living in a more arid climate such as lilac, ceanothus, feijoa (pineapple guava), bearded iris, survive on very little rainfall, many are drought tolerant plants and can exist on soils that have a pH of 7.0 (neutral) or higher.

So I think if you start studying climates and the plants that inhabit them, you will quickly get a feel for what may be acid loving or not.

It really is a fun way to learn plants, plus, that is how some of the best landscape designers do it, they study nature and its perfect use of plants.

Question #3:  Should I Prune Rose of Sharon?

Question:  I planted a Rose of Sharon bush in my flower garden just last summer. It is my understanding that rose of sharon bushes can become quite large and can take over a space. Is it better for me to remove this plant now before it gets too big, and effects other flowering plants, or do you disagree about Rose of Sharons getting large? If it turns out that I should remove this plant, should I let it stay it the ground until the end of this summer so it can increase its health before it gets transplanted? Also what is the best way to prune Rose of Sharon plants so they don't get too big?

 Chantelle, Ontario, Canada


ANSWER:  Hi Chantelle! I get tons of questions about Rose of Sharon (Hibiscus syriacus); I think it must be one of the most planted shrubs! I can see why, they are beautiful.

It depends upon what you feel is too large. What may be too large for one gardener is not large enough for another - you know? Let's take a look, and you can decide for yourself.

Rose of Sharon is a deciduous shrub that grows up to 10 to 12 feet (3-3.6 m) tall, and up to 6 feet (2 m) wide.

They start out with fairly compact growth, but as they age, they do tend to open up and spread.

Now Rose of Sharon are super easy to prune and to train into just about any shape you want. They can be easily trained to a single trunk with a treelike top, or as an espalier, or as a hedge.

If you feel it is encroaching into your other plant's space, you can easily prune it back to control it.

The best time to prune and transplant is in the winter while it is dormant. Basically you can prune it to any shape you want, and yearly pruning will keep its size in check. After it has finished flowering is also another good time to lightly prune it back if summer growth has gotten out of control.

It's totally up to you, but I think you will be able to work with it where it is and enjoy its beautiful shape and flowers. Good luck!

Question #4:  Blossom-End Rot On Peppers

Question:  I have 7 capsicum plants growing in a raised bed. There is plenty of fruit on them but I am getting quite a few with blossom-end rot. I try to water just once a week but go to twice when we have a few really hot days without respite. I shade them when the temperature gets over 33° C (90° F). Is it likely to be a calcium deficiency or a watering problem? The PH is around 6.5.

 Sylvan, Adelaide, South Australia


ANSWER:  Hi Sylvan! Well, you kind of answered your own question! Capsicum, or peppers (including everything from sweet bell to hot cayenne), and tomatoes both suffer from blossom-end rot which is a calcium imbalance in the plant which is due to inadequate and uneven moisture.

When there are large fluctuations in soil moisture, the roots can't take up enough calcium. The solution is to keep the plants uniformly watered throughout the season. Water deeply, to about 6 inches (15 cm) down, and then mulch to conserve the water during the hot weather.

Try not to let the soil get too wet or too dry, but evenly moist, without being soggy. It sounds like in your efforts to conserve water, you are causing the problem.

Even out your watering habits, use mulch to keep the soil moist, conserve water, and keep the roots cooler, keep your plants covered as you have in super hot temperatures to avoid sunscald, and your blossom-end rot will go away.

Question #5:  When To Prune Geraniums?

Question:  When is the best season to prune Geraniums?

 Johan Schneider,Punta Umbr´┐Ża, Huelva, Spain


ANSWER:  Hi Johan! I don't know what kind of Geraniums (Pelargonium) you have, but I am going to assume you are talking about garden geraniums, not ivy or true geraniums.

Geraniums are perennials that, in warm climates with mild winters can be evergreen, or in colder areas are a summer annual that need to be brought indoors, or cuttings taken for the following year.

The best time to prune geraniums for size and shape is during the early spring or fall. You want to prune them back before they start actively growing and getting ready to flower.

You really only want to prune geraniums back when the plants become stringy or misshapen, and have long stems with leaves only at the tips, and flowering has slowed down, then you should consider pruning.

Clean out any dead shoots or leaves at this time as well, and in a few months your plants will look terrific!

Question #6:  Don't Prune Roses?

Question:  I recently saw a garden show on TV where a Marin Co. nurseryman said there was a study about "to prune or not to prune" roses. He stated not pruning resulted in healthier plants. What say you?

 William Clemence, Redwood City, CA, USA


ANSWER:  Hi William! Well, I guess we can't believe everything we see and hear on television can we? (Kidding) Gosh where do I start with a statement like that! Wow! Perhaps he misspoke himself?

I have been working with roses for years, and I would emphatically disagree with that statement. Roses go downhill, get leggy, stop flowering, become more disease and pest prone, and many other problems when they don't get pruned regularly.

My parent's roses are a great case in point. I pruned them for years and they looked great. Then my parents took over their care and they didn't get pruned for years. There was no comparison over time in performance, health, and vigor, they all went drastically downhill.

One comment that I have heard about pruning roses is to wait until very early spring to prune, when the buds start to swell, instead of pruning when they are totally dormant, but I have never tried it. I don't see that it would do much harm as long as you did the pruning before the plant was actively growing. If you did it too late in the spring, then I think it would be counter-productive.

I personally don't mess with success. I prune roses every year, and I do it when they are fully dormant, and they look spectacular.

Thanks for sharing the comment, it was really interesting!

Question #7:  When To Prune Fruit Trees?

Question:  When is the best time to prune fruit trees?

 Lynn Kirkham, Liphook, England


ANSWER:  Hi Lynn! The best time is during the winter, or when the trees are fully dormant. Many fruit trees like various plums and apricots, bear fruit on new wood and annual heavy pruning is necessary if you want fruit. Others like apples, bear fruit on old wood and spurs, so they simply need light thinning and shaping every year.

If you have an apple, you can read our tutorial in the How To Section of our site: How To Prune An Apple Tree.

Question #8:  Kill Poison Ivy

Question:  Moved to the country and we have lots of poison ivy. It's dead now, but will be coming up in the spring. Any suggestions on how to get rid of and kill?

 Beth Swalwell, Dorsey, IL, USA


ANSWER:  Hi Beth! I'm not a big proponent of using chemicals in the garden, but when you get noxious plants like poison ivy, I do turn to chemicals. When used properly, chemicals can be helpful, and for me, this is a perfect time to use them.

Here is what I would do with your problem. In the spring when the plant starts actively growing and the outdoor temperatures are around 65 to 80 degrees F (18.3 to 26.7 C), I would use a product called Brush-B-Gon Poison Ivy Killer. You can find it at,, and any garden or home improvement center will carry it too.

Wait until the hottest part of the day and then pour the Brush-B-Gon, undiluted, on the plant making sure to cover it thoroughly. This product can kill entire tree stumps, roots and all, so I know it will kill the poison ivy right down to the roots. I would wait 2 weeks and apply the Brush-B-Gon one more time. It will solve your problem.

Be careful not to get any of the Brush-B-Gon on any other plants or they will be killed too. This is a non-selective herbicide and it will kill anything it touches.

Lastly, clean up any debris of the dead plant and leaves because the oils will stay around until you clean everything up. Wear gloves and goggles and be careful not to get any sap on your hands or skin. Put all debris in a plastic bag, seal it, and put it in the trash.

Once the plants are dead, and the debris is cleaned up, you'll be in the clear. Good luck.

Question #9:  Fix Thinning Lawn

Question:  Is there a feed I could use to thicken up my lawn, as it's very patchy with some bald parts?

 Nerys Williams, Aberaeron, Wales


ANSWER:  Hi Nerys! Actually the best thing to do would be to overseed it. Depending upon what kind of lawn you have, you can't count on a fertilizer to get the grass growing so vigorously that it will fill in large bald spots.

You're in luck we did a 2-part series on lawn care and the second part will help you out because it talks about how to patch, overseed and start a new lawn.

Here are the links:

Grow a Green, Lush Lawn - Part 2
Patching, Overseeding or Starting a New Lawn

Grow a Green, Lush Lawn - Part 1
Choosing the best grass variety for your area

In addition, I would start composting your lawn at least twice a year, that will do wonders too.

Here is the link:

How To Compost Your Lawn

Read the above articles and your lawn is going to look fantastic! Thanks for the question.

Question #10:  Growth Regulator For Hedges?

Question:  I read some time ago that there was a product available that could be sprayed onto private hedges to arrest their growth. Do you know if such a product exists and if it does where I could get some from?

 Lawrence Lowe, Penkridge, Staffordshire, UK


ANSWER:  Hi Lawrence! Yes, there a couple of growth regulators. I'm not a big advocate of them simply because I don't like to spray chemicals around unless I am absolutely forced to, but I understand other's needs vary from mine!

There are two products. Florel is one, the other is called A-Rest. Growth regulators are used regularly in the greenhouse industry to keep ornamental crops short and compact, but people do use these products outdoors on bedding plants, roses, trees, and shrubs and they also use them to abort fruit crops.

I caution you to be very careful when applying and follow the directions on the label. If you use too much you can burn your plants, but you can also stunt them for a long time. They will come out of it, eventually, but I think you want to just slow the growth, and not stop it permanently!

Also be careful when applying and do so AFTER any fruit has come to bear if you have fruit trees around. If you spray these products on trees before they fruit, they will abort their crop, which, in some cases, is what people want.

Here are some links to the products. These are used worldwide, so I know you will be able to find one or the other where you live.



Question #11:  Can I Plant Caesalpinia ferrea?

Question:  I want to plant a cluster of three leopard trees (Caesalpinia ferrea), but a sewage pipe runs through the area approx 1.5 meters (5 feet) deep. I have been unable to find info on the root system of this tree and would like to know what type of root system it has before planting. Also I have read that the trees should be spaced 6 to 9 meters (20 to 30 feet) apart and I want to space them 3 meters (10 feet) apart to form a dense cluster. Will this affect their growth?

 Jimmy Smith, Pretoria, Gauteng, South Africa


ANSWER:  Hi Jimmy! I applaud your efforts to get information before planting! So many people just plant, and then when the problems arise, scramble to fix the situation.

The Brazilian Leopard Tree (Caesalpinia ferrea) does have very aggressive and invasive roots, and I would not plant one over a sewer pipe.

Also, they grow up to 10 meters (30 feet) tall and 5 meters (20 feet) wide. They are a very attractive tree that sheds its bark in large flakes, leaving a patchy grey and white effect on the trunk, but they are fast growing.

If you did end up planting them, I don't think I would plant them as close as 3 meters (10 feet). It would not affect their growth, but you would have such a dense hedge! 4 to 4.5 meters (15 feet) would be a better spacing for them. They will fill in quickly, don't worry!

They are an excellent garden specimen for the bigger garden, and since I have no idea how much space you have, I would plant this particular tree carefully. Thanks for the good question!

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