Root-prune large gardenia before moving it

By Audrey Post
MS. GROW-IT-ALL®

Q: We have a large gardenia bush in our yard that has overgrown its space and needs to be removed. It’s probably 6 feet tall by 4 feet wide. Is it too large to move to another spot and if not, what’s the best way to do it? It’s about six years old.

A: They look so cute when we bring them home in their little 1-gallon pots that it’s sometimes hard to visualize how large they’ll eventually become. And when they do outgrow their spaces, we like to think it’s because of our skill at site selection – “It was just so happy there!” -- and the excellent care we gave them.

But regardless of the reason, whether planted in too small a space, changes in available light because of new construction or tree removal, or supercharged genetics, small trees and large shrubs sometimes need to be moved. Root-pruning is the best way to prepare your gardenia bush for the big move.

The theory behind root-pruning is that by severing the long roots that extend beyond the drip line, you force the shrub to grow new feeder roots closer to the trunk. These feeder roots will be part of the root ball when you dig the gardenia and move it to its new location in several months, so the shock to the gardenia’s system will be lessened.

Take a flat spade or shovel and thrust it into the soil about 15 inches out from the trunk of your shrub. Make sure you push the shovel down about a foot so you cut the roots running laterally. Now make another cut right next to the first one, and another one next to that one, until you have a circle extending around the shrub. You’ll need a sharp spade to cut the roots. If you encounter a particularly thick one, you can use loppers to snip it.

Ideally, you wait about six months after you root-prune to move the shrub, but three months is the minimum. If you root-prune your shrub this weekend, it should be ready to move by February or March. April is probably the latest you want to move it because May is when the summer heat really starts cranking up.

The heat is the same reason you want to root-prune in fall and transplant in spring in the Deep South. Growth is slowed over the winter, so the severed roots won’t hurt the plant the way they would in summer, when it’s in growth mode and dealing with heat stress. In areas farther north with less intense summer heat, the reverse would be true: Let the shrub grow new feeder roots over the summer so it can survive a cold winter.

You’ll probably need to prune the gardenia back a bit when you move it, but don’t whack it all the way back. The old argument for drastic pruning when you move a shrub was that the root-ball couldn’t support the entire plant, because it lost the feeder roots when you dug it. By root-pruning, you lost those feeder roots several months earlier and the root-ball that you dig is actually what was supporting the entire bush.

Besides, you need those leaves for photosynthesis to feed the plant and help it get re-established.

Don't fertilize Knock Out® roses until spring

By Audrey Post MS. GROW-IT-ALL®

Q: We have 11 Knock Out® rose bushes, which my husband feeds two-thirds of a cup of 6-6-6 Blooming Rose Fertilizer monthly. They have grown to about 4 feet high and bloomed beautifully over the spring and summer. Should we keep applying rose food throughout the fall and winter months? Also, should Knock Out® roses be pruned? If so, when should we prune them and how much?

A: Knock Out® roses have become among the most popular shrubs in the home landscape, thanks to their ease of care and prolific flowering. They’re disease-resistant, drought-tolerant and self-cleaning – meaning no dead-heading of spent blooms. They’ll bloom from spring until the first hard-freeze.

I would lay off the fertilizer through the fall and winter months. You might get a few blossoms here and there as our temperatures do their normal fluctuations, but you don’t want to keep the plants in high gear for growing and blooming over the winter. New growth is more susceptible to freeze damage, and consequent damage to the entire plant might result.

If you have room to let them continue to grow larger and they’re holding a good shape, leave the pruning shears alone. If you want to keep them to a smaller size and shape, prune them in early spring – which for North Florida is February. It’s a matter of personal choice and space. One friend said hers grew to a 6-foot tangled mess the year she didn’t prune them; another never prunes hers and they stay about 4 feet tall and wide. Soil and climate differences can play a big role.

If you choose to prune your Knock Out® roses, cut the shrub back to about 12 inches. As it grows throughout the season, use hand-held pruners to snip off wayward branches that are outpacing the others to maintain the shape.

Q: When Tropical Storm Fay blew through in late August, most of my sloped back yard was under water for a few days. The St. Augustine grass at the top of the slope, closest to the house, seems to have recovered but the grass farther down where it is shadier is still looking sad. What should I do?

A: From your description, it sounds as though the grass at the bottom of the slope was under water longer, so it makes sense it would take longer to recover. Lack of oxygen can drown plants as well as people.

The fact the area is shady is probably slowing down the drying-out process. Make sure there’s no mulch helping to hold in moisture right now – you want to give the water a chance to evaporate – and wait and see. Anything else you do right now would probably interfere with your grass’ ability to recover on its own. Grass slows its growth this time of year, so not seeing new growth doesn’t mean it’s dead.

If the barren appearance bothers you, spread some ryegrass seed over the area once it’s no longer soggy. If it sprouts, you’ll know the area is drying out and your St. Augustine likely will reappear next spring. If not, you’ll have to decide whether to re-sod, plant something else or create a mulched area.

Remove oleander caterpillars while young

By Audrey Post
MS. GROW-IT-ALL®

Q: Big hairy worms have been giving me fits for the past seven years, eating the leaves on my mandevillas. I use the white powder and maybe it cuts the population, but I hate the way it makes my plants look. What else can I use that will kill the worms but not kill the plant? I am attaching a photo so you can see what a charmer this is.

A: Yes, indeed, that is one charming pest you have there. It’s a Syntomeida epilais, commonly known as an oleander caterpillar. Supposedly it feeds only on oleanders, but it obviously has developed a taste for mandevillas – as your photo illustrates. Through a little research I learned that its original host was a pineland vine that is now rare, so it has been known to try new foods.

A mature oleander caterpillar is orange with tufts of black hair and is about 2 inches long. The adult moths are purplish-black with white dots on their wings and are sometimes called polka-dot wasps. They reproduce three generations a year, and sometimes the process overlaps and you can see larvae and moths at the same time. They’re really rather exotic looking, but they can be devastating. While they usually don’t kill the plant, they can defoliate it and leave it vulnerable to diseases that can kill it.

This is one caterpillar that birds and small mammals have learned to avoid because its primary diet, oleander, is so toxic. There are beneficial insects that will eat oleander caterpillars -- predatory stinkbugs, parasitic flies and wasps, even imported red fire ants eat the clusters of eggs – but the best way to control them is to pick them off by hand. The spines generally pose no threat to humans. [Ms Grow-It-All® update: A subsequent column, post date Dec. 17, 2008, discussed one person's allergic reaction to the oleander caterpillar, so use gloves to pick them off just to be safe.]

The egg clusters can be found on the undersides of leaves, and you can scrape them off into a plastic bag – a newspaper bag works well for this – and throw them in the trash. Young larvae, which are more yellow than orange, eat the tissue between the veins on the leaves. Snip off the infested leaves, but them in a plastic bag and then place the bag in the freezer for 24 hours to kill the caterpillars. Larger larvae can be picked off, placed in a plastic bag and frozen the same way, or dropped into a can of soapy water.

Obviously, it’s hard to pick larvae from large oleanders because of the height, but a mandevilla vine should be easier to manage. Horticulturists recommend your friendly white powder, Bacillus thuringiensis, for large plants.

The key appears to be catching them while they’re young.

Q: What should I do to try to save a hanging spider plant that was left outside when we had frost? The leaves have turned black and slimy.

A: Those cold nights sometimes sneak up on us, and different microclimates in our yards and gardens sometimes get colder or warmer than the “official” temperature recorded. It could have been 37 at the airport but 32 on your porch.

If it wasn’t too cold for too long, the plant might survive. Cut off all the slimy, damaged foliage and clean up any debris on the soil surface. You can bring it inside, give it some water and see if it starts to grow again, or you can skip the water, move it to a protected location such as an unheated shed and let it rest until spring.

However, unless it’s a variegated variety or a sentimental favorite, I’d pitch it and start over next spring with something else. Solid green spider plants have become invasive in the ground here in North Florida, and those airborne babies can make that leap from the hanging basket to the ground very easily.

Mechanical help needed to remove big azaleas

By Audrey Post
MS. GROW-IT-ALL®

Q: We bought property near Lake Talquin a couple of years ago, and the former owners had planted azaleas everywhere – and I mean everywhere. There’s no pattern to it, and unfortunately, no lawn. We need to get rid of some of them. What’s the best way? Will Roundup work? They’re about 20 years old and we tried digging one out and it took hours.

A: This is a great example of a bit of ancient gardening wisdom: Any plant in the wrong place is a weed. Some weeds are easier to remove than others, and as you’ve seen, this isn’t one that you can simply tug and it will spring free.

Roundup® and other chemical sprays are designed to be absorbed through the foliage and move through the plant, eventually killing the root. They work fine on soft-stemmed weeds, but they are not the most efficient way to kill shrubs. It would take repeated applications over a long period of time, which would cost a lot of money and likely leave the area so toxic that grass wouldn’t grow. Even products designed to kill woody shrubs take a while, and a 20-year-old azalea in good health could probably withstand a couple of applications. It wouldn’t look good, which would just add to your problems, but it would survive. And you’d still have to dig it out.

The easiest way to get azaleas out is with heavy equipment, such as a backhoe, which can scoop out the bush and its roots in one bite. If that’s not an option, either because of the cost or because of the potential damage to other landscaping, you’re going to have to dig them out by hand.

Before you start hauling azaleas out of there, do a little prep work to make sure you’re removing the right ones. It sounds like you want to end up with a lawn and have the remaining azaleas create a pleasant pattern, Try to visualize what a spot will look like without each azalea that you want gone. One technique is to take a digital photo, then edit out the shrubbery. A low-tech version is to get photo prints and cut out the azaleas you think you want to remove, then lay the photos on paper and color in grass or dirt where the azaleas were. If you like the way it looks, great. If not, it’s easier to print a new photo than re-grow a 20-year-old shrub.

Prune the azaleas to 18 inches to 2 feet high. Rake back all the mulch and cut every surface root you see with a shovel. Then dig about 2 feet down and 2 feet out all the way around, using a pickax or mattock to cut larger roots. The shrub may start to give a little when you pull on it, but it still has a taproot holding it in. You’ll have to dig out around the tap root to be able to cut it.

Yes, it’s a lot of work. If you have a heavy truck or tractor, you can hook a chain around the base of the azalea and pull it out, but it’s much easier if you prune it and cut the side roots first. Also, you can water the azalea to soften the soil before you pull it out, but makes sure you keep the water on the azalea and not on the ground where the truck will be. Otherwise, you’ll end up with ruts in your yard or even worse, your truck mired up to the axles.