Garden Answers

Shrubs

Do ornamental grasses attract or create problems with gnats?
If it has snowed a lot, do I still need to water all my trees and shrubs?
Can I prune everything back in Fall?
It's May and my Chitalpa tree and Rose of Sharon aren't doing anything?
My Cistena Plum has reddish-purple spots and holes in the leaves?
My Corkscrew Willow has a strange chunky "bark" at the base?
We pulled out some bushes and the roots that stayed intact are sprouting?
How moist should a Dwarf Burning Bush and Japanese Maple be?
What can I prune back in late October?
Should Japanese Maples and Rhododendrons be sprayed with Wilt Pruf?
Is it okay to plant during the hot months of summer?
Is early Spring the right time to be pruning?
Which plants are drought-resistant?
How do I create a hedge with Mohican Viburnum?
What are the best light conditions for an Endless Summer Hydrangea?
Can you suggest a hedge of evergreens to block a road?
How far can we cut back roses in order to paint?
What can you tell me about Crepe Myrtles?
20-year-old corkscrew willow losing its bark and branches?
Do you have any tips for transplanting shrubs?
How do I care for my ornamental grasses for the winter?

Question: Do ornamental grasses attract and/or create problems with gnats. Is this a recurring problem with ornamental grasses?

Answer: The truth is that pretty much all plants will attract insects to an extent. Insects like the shelter, coolness and humidity provided by the plants. Ornamental Grasses will attract insects I suppose, but they're no worse than any other plant. The biggest problems I've seen with insects are usually associated with over-watering. If the area stays wet, you'll generally see more insects. The solution is to soak the plant well when you water it, but allow it to dry slightly before soaking it again.

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Question: We've had a lot of snow recently, and I'm wondering if I still need to water all my trees and shrubs.

Answer: Well, that depends upon how much snow we get through the rest of the season. Generally, we don't get much moisture from snow cover here in the Grand Valley. The problem is that we get a good layer of snow and then the sun starts to melt it away. What melts from the bottom certainly adds moisture to our soil, but the majority of the snow actually vaporizes into the atmosphere. If we continued to have storms that kept the ground covered every couple of weeks, we probably wouldn't need to water because it also acts like a mulch covering the ground and helps cut down on water loss. Unfortunately, the snow doesn't usually last long enough for us to completely stop our watering. It does, however, enable us to lengthen the intervals between watering. If, for example, you normally water every 3-4 weeks, you might be able to push that to 5-6 weeks.

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Question: Can I prune everything back in Fall?

Answer: Personally, I think it's okay. There's an old adage that says, "The time to prune is when the saw is sharp." I take that to mean that when you're ready, go ahead and do it! While some folks debate the advantages of pruning at one time over another, I think most are minor points.

Having said that, however, I think it's important to know why you're pruning. People often think they have to prune to keep the plant healthy. That's not necessarily true. In fact, it's probably better not to prune than to do it incorrectly. Come on out if you have questions, we can offer advice and have books you can look at; or go to the extension office-they have good do-it-yourself fact sheets on pruning.

In general, March (late Winter/early Spring) is the best time to do your pruning. The timing is good, because this is before plants are breaking their dormancy, consequently, this is much less stressful on them. There's also the added benefit that soon the plant will be actively growing, so that any pruning cuts can more quickly begin to heal. Another advantage to spring pruning is the fact that with the leaves off of the plants it's much easier to actually see what you're actually doing!

Lots of folks like to prune in the fall when the plant is beginning its dormant stage. The problem I have with that is that pruning leaves an open wound which will not heal over while the plant remains dormant. Sometimes, though not often, this becomes a place of easy access for pests and/or diseases. The chance is small, but not one I'm comfortable taking, which is why I prune in the spring.
I have had some folks who tell me that they travel and don't get home until sometime in May. In those cases, I tell them to go ahead and fall prune; it's better to prune then, than not at all!

People ask me about using pruning paints, and I have to say that I'm not really a big fan of them. Plants have been able to get along fine healing on their own without a "Band-Aid" to help them out.
I think pruning paints are more to make us feel better than anything else. In some cases they can actually create a more favorable environment for disease by creating a dark, moist place for spores to thrive. I'd rather leave the cut open to the circulating air.

The same goes for amber shellac. Though it has an additional antiseptic property which can kill spores, I still think it's more of a "feel good" thing for us than good protection for our plants. I'd rather make a clean cut and leave a plant alone. Hope this helps.

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Question: I'm worried about my Chitalpa tree and my Rose of Sharon. I did winter water them, but its May and they're not doing much of anything.

Answer: I wouldn't worry about your tree or shrub at this point, especially since you winter watered them. If you were to check out what we have here at the nursery, you'd find that our plants look the same. Lots of folks have been calling about some of the later-blooming trees and shrubs. The Catalpa trees and Rose of Sharon are typical of this group, which also includes Trumpet vine, Engleman Ivy (also known as Virginia Creeper or Woodbine), and Perennial Hibiscus. They just need a little more time to come out of dormancy, warm up and start producing buds. Though the branches may look dead, if you gently bend them, they should still be pliable, and if the bark is lightly scratched, you should see green just beneath the surface-a good sign of a healthy plant. Most of these plants start showing signs of budding by mid-May. If you still don't see anything by the end of May, you may want to give us a call.

Similar to these are the Chitalpa trees, which warrant a word of caution. They are not totally hardy here, and we expect some die-back over the winter on these guys, especially as cold as it was. It may be that the plant may die back to the ground. If that happens, don't get discouraged! First of all, wait until the middle of May and the cut off all of the dead stuff. Chitalpas grow VERY quickly and they will zoom back 6, 8, or even 10' in a year, all the while blooming all summer with their beautiful flowers. Even if they die back to the ground every winter, I think they're still worth doing.

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Question: My Cistena Plum has something wrong with it. Its leaves are covered with reddish-purple spots and there are holes in lots of the leaves. What's wrong with it? Am I going to lose the plant? Is there anything I can do now?

Answer: Sounds like you've got Shot Hole Fungus. It's common among the Prunus family and seems to show up whenever we have a stretch of higher humidity. One thing you can do is to be sure your plant is being watered at ground level and not from overhead sprinklers. Moisture on the leaves or artificially raising the humidity around the plant can lead to fungus. Aside from that, there's nothing to be done right now. After the leaves drop in the Fall, you should use a Copper Fungicide or Bordeaux Dust on your plant. Be sure to clean up all the fallen leaves and dispose of them; making sure NOT to use them in any compost piles.

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Question: There's something growing at the base of my 4 year old Corkscrew Willow. It's brown and hard, kind of like a bark mulch, but very chunky. What is it? Can I just take it off? Will it hurt the tree?

Answer: Without seeing it, it's difficult to know for sure, but it sounds as if you may have Crown Gall. If you see it anywhere on a branch, the best thing to do it to just cut that branch off. When it's at the base of the tree, as yours is, there really isn't anything you can do. Cutting off the galls doesn't work because they'll simply grow right back again. Crown Gall is a bacteria that enters through wounds in a plant. It can damage or kill the tree, but usually takes many years to do so. There is a material called "Gall-X" that can help get rid of the galls, but I'm not exactly sure where you might find it. I'd suggest calling one of the Co-Ops or Randall Industries. Hope this helps.

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Question: We have pulled out some twenty-year-old bushes that have thorns and orange berries on them. I think they are Pyracantha. Where we pulled them out, the roots that stayed intact are sprouting. We have sprayed them twice with an herbicide (Trailblazer), do you have any suggestions?

Answer: The shrubs that you removed do sound like Pyracantha to me. The best way to kill the sprouts is to treat them with a Fertilome product called Brush and Stump Killer. You can mix it with water and spray it on the foliage or cut the stumps back again and apply it full strength to the freshly cut ends (that's what most people do). The product is a systemic and will work its way down into the plant and kill the roots. Be careful with this product, it's potent! Don't slosh it all over the place. If you soak the soil, it can sterilize it for up to a year. Also be very careful not to let any of the material get on adjacent desirable plants. This product kills the entire plant, so unless you want to get rid of your aspen trees, I wouldn't use it to control the suckers from your aspen. Hope this helps.

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Question: I just planted a Dwarf Burning Bush and a Dwarf Japanese Maple. How moist should I keep those plants?

Answer: Neither of these plants is terribly drought tolerant, however you don't want to keep them constantly wet either. You'll have to strike a balance. When you water, be sure that the plant is soaked well. An hour or so after watering the soil should be muddy wet 12" to 18" down (dig down to check). You then need to allow the soil to dry a little before soaking it again. Dig down three or four inches to check the soil. You don't want it to get bone dry, but it should be showing a little dryness (one of my clerks called it "the dry side of moist"). I would guess that at first you should be watering once a week to twice a month. The important thing is that you need to dig down and check how the soil moisture is doing. Also remember that's it's helpful to the plant to water it through the winter. Wait until the air temperature is above 32° and soak it well every three to five weeks, depending on the weather. Hope this helps.

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Question: Several of my shrubs are growing out-of-control! What can I prune back in late October?

Answer: If you really need to do any fall pruning, the first thing you need to do is to make SURE that the plant is dormant before you start cutting. Usually that's indicated by the leaves turning colors, and most, if not all of them falling from the plant. If you prune before a plant is dormant, you run the risk of stimulating new growth-something that you really DON'T want to do now. Generally, I prefer to prune in March. The reason for that is that when you prune, you're making a wound in the plant which needs time to heal. Pruning now will leave that wound open all winter and that tissue may desiccate and die back. The wound is also an inviting opening for diseases and insects to invade the plant. Pruning in the spring, just before new growth begins, gives the plant an opportunity to begin healing the wounds up as its emerging from dormancy.

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Question: I have some Japanese Maples and Rhododendrons that I was told should be sprayed with Wilt Pruf. When should I use this?

Answer: Wilt Pruf is the brand name for an anti-transpirant. It's sprayed on plant to cut the water loss which normally occurs as water transpires through the stomata (or pores) of leaves. Basically, an anti-transpirant is a wax that lightly coats foliage and slows the natural transpiration rate. This is very helpful for broadleaf evergreens and any plants not well-adapted to the low-level humidity typical of our climate. It should be used during the winter months and NOT during the growing season unless you are transplanting.

The best time for use is when the plant is dormant: the end of November or beginning of December should work fine. Be sure to cover both the upper and lower surfaces of the leaves. A single application usually lasts several weeks. You may actually only need one application for the winter, but that really depends upon the weather and exposure. Sun and moisture will break down an application more rapidly. Do be careful not to over apply, as the build up can hamper the plants transpiration and actually hurt it.

Another great use for Wilt Pruf is for keeping Christmas greens from drying out. Using it on wreaths and garlands helps them maintain moisture and gives them a shiny look! Hope this helps.

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Question: Is it okay to plant during the hot months of summer?

Answer: Absolutely! Traditionally, we did most of our planting in the spring when plants were only available bareroot. The plants came to the garden center from the grower dormant with no soil around their roots. They were much easier and lighter to ship. Bareroot plants had to get into the soil in the spring, so they could break dormancy and get established before the stress of summer.

Now, almost all of our plants are containerized. They come with a well-developed root system in a pot of soil. With careful watering, they are more than equipped to thrive and grow in the heat of summer. In fact, containerized plants have extended our planting season quite a bit. In fact, we recommend planting in Western Colorado until the ground freezes. You should only avoid planting in frozen ground, because it's just too much work. Gardeners are a little crazy, but we're not dumb!

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Question: Is early Spring the right time to be pruning?

Answer: This is a great time to do your pruning. But before you run out into the yard with your pruning saw, let me give you some basic guidelines. Most plants do not have to be pruned to be healthy. When pruning an ornamental plant, limit pruning to the removal of dead, diseased, damaged, or badly placed branches. A badly placed branch would drop leaves into your neighbor's yard, cause head injuries to people walking on your sidewalk, or create a weak crotch that could be broken by a strong wind. The proximity of power lines would be another concern.
The point is, have a good reason for cutting off a branch.

It's important to do a good job with pruning. When cutting around the branch collar, you're working with the plant's physiology — how the plant protects itself against disease. (You can see what the branch collar is like and some tips on how to prune in our Shade and Ornamental Tree Gardening Guide included on this website.) This could affect the health of the plant. Pruning can be an intimidating, complicated task. Come in and talk with us. We'd be happy to talk you through it..

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Question: Okay, I'm ready to just "do in" all of my grass in my front yard. Fortunately, I have a small area and much of it is already in decorative bark, but I want to eliminate the rest of the grass. One problem, I'm stumped over which plants are drought-resistant. Can you help?

Answer: You betcha! I'm glad to hear you're looking for ways to conserve water. Lawns are the biggest users of water in our yards. Our clerks have attended seminars on drought-resistant plant materials, so we're ready to help you. We carry native plants, Plant Select (plants chosen by experts for their appropriateness in Colorado gardens), and tons of other resources.

Before coming in, measure your yard carefully and sketch your project area. Draw in existing plants, make note of windows, and label the compass directions. The plan will help us determine how many plants you'll need and make space limitations clear. We want you to be happy with the oasis your yard creates.

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Question: I have four Mohican Viburnum shrubs which I planted last October in a space about 25' long by about 6' wide. When and how much should I prune these to help create a hedge from these shrubs?

Answer: You made a great choice with Mohican Viburnum. I have a couple in my yard and love them. This variety of Wayfaring Tree Viburnum is especially compact with a symmetrical, dense, rounded growth habit. The dark green, heavily veined, almost "quilted" foliage makes a nice backdrop in the landscape and is especially good as a screen or informal hedge. The flowers show up especially well against that foliage. Mine bloomed about three weeks ago, displaying beautiful white flowers in flattened and slightly domed clusters all over the shrub. The berries are green right now but will turn bright red in mid summer and then black. The robins in my yard love eating those things!

If my math is right, you've planted the plants a little more than 6' apart. That's maybe a little farther apart than I would have put them. They will fill in to form a solid hedge, but it's going to take a little longer for that to happen. For a solid screen, I usually recommend planting them about 5' apart. Having said that, there's probably little pruning you need to be doing right now. The plant naturally grows thick and dense so you don't have to prune them to encourage better density. In fact, with the size of the bed you have them in, there will probably be little pruning that you'll have to do. Their mature height is about 6' with a 6'-8' spread, so there may a little pruning to do to keep them within the 6' width of your bed, but that shouldn't be for a number of years.

Because of their naturally dense, attractive growth habit, most people do very little pruning on this plant unless there's a branch growing out in the way somewhere. If you do need to prune it, the best time of the year is right after the plant is done blooming. You see, Viburnums set flower buds in the late spring for next year's bloom. Those buds are generally at the tips of the stems, so if you shear the plant in the summer or fall, you'll be cutting off the flowers for next spring. Pruning it right after flowering will give the plant a chance to grow out and set flower buds for the following spring.

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Question: I've recently purchased a hydrangea (Endless Summer). The tag says it should be planted in filtered light. I don't believe I have a spot with filtered light. I have watched the clock to see when certain areas receive shade. Each spot I've chosen receives at least 4 hours of sun per day. One is 4 hrs of morning-early afternoon sun, one is afternoon sun, and then one is late-afternoon/evening sun. Would any of these areas be suitable? Please let me know what you think.

Answer: Varieties of Bigleaf Hydrangea really do need quite a bit of shade here in Western Colorado. In cooler, more humid climates they can take more sun, but even there they appreciate afternoon shade. We tell people to plant them in full shade (if possible) in this area. They will take some early morning sun, but would be happiest with shade by 10:00 or 11:00 in the morning and then throughout the rest of the day.

Hydrangeas like a rich, organic, well-drained, somewhat acidic soil. Mix in a lot of a decomposed organic amendment (such as Soil Pep, Peat Moss, or Compost) with your soil well around where the Hydrangea is to be planted. They are happiest when they're planted around other plants because that helps increase the humidity; something Hydrangeas really need.

Having said all that, 'Endless Summer' is a wonderful variety of Hydrangea. Most of the Bigleaf Hydrangeas are not truly winter hardy here, and those that survive are usually frozen down to the ground. That's not a big problem as they sprout readily from the roots and quickly grow back in the spring. The problem is that the flower buds are usually produced at the tips of last year's growth and when it freezes over the winter, you lose the flowers. 'Endless Summer' will flower on current year's growth so when it freezes down, it will resprout in the spring and bloom for you later on in summer. Hope you can find a spot for your plant where it'll be happy.

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Question: I want to plant a hedge of evergreens to block out a major road. A native species, about 8 to 15' tall would be perfect. Can you give me a suggestion?

Answer: Probably the best choice for what you have in mind is an upright juniper. They are tough, durable and drought tolerant. Though we do have a native species of Juniper here in the Valley (Single Seed Juniper--Juniperus monosperma), I'd recommend that you use a variety of Rocky Mountain Juniper (Juniperus scopulorum). Single Seed Juniper is extremely slow growing when grown without supplemental irrigation. Rocky Mountain Juniper is native to higher elevations here in Colorado and consequently requires a little more moisture to thrive.

There are a number of good ornamental varieties of Rocky Mountain Juniper available. We normally carry 'Cologreen', 'Gray Gleam', and 'Wichita Blue'. Once established, they will grow well if given a good soaking once a week to twice a month during the growing season. One possible problem is that these plants will eventually get taller than you specified. They will usually max out at 18' to 25' tall. If that's a problem, they can be sheared two or three times a year and kept at the height you desire. Another alternative would be to plant a shrubby variety like 'Mint Julep' which will grow to 8' in height. However, it will take ten to twenty years for the plant to achieve that height.

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Question: Some large, overgrown roses are growing up against our house in Marin County that I need to paint. I’ll have to cut them back for access and I’m not sure what to do. If I cut them back, how much should I cut and will they survive?

Answer: Go ahead and cut your roses back to paint your house. Though they should be pruned right at first bud, it won't hurt the plant significantly to cut them back now.

Cut them back somewhere in the neighborhood of 18" to 30" from the ground. While you're at it, try to "renovate" the plant by removing old, large canes in favor of younger, more vigorous canes. Those younger canes will be fuller, grow more quickly, and flower better than those old worn-out canes.

After pruning them back, be sure to water them regularly and fertilize them lightly with a good rose fertilizer.

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Question: I've recently purchased some Crepe Myrtle trees (Pecos, Zuni, and Tonto) and am wondering what can you tell me about them. I was under the impression that I was buying a tree (7 ft when fully grown), but everything I've read about them seems to say that they should be cut back each spring. They’re all showing new growth, but nothing on the old wood. As these reach maturity, how far do they need to be cut back?

Answer: Crepe Myrtles are marginally cold hardy here in the Grand Valley. Only the more cold hardy varieties have a good chance of survival here. The National Arboretum has been doing some breeding work with Crepe Myrtles to increase their cold hardiness. All three of the varieties that you have are good ones for cold hardiness. 'Pecos' is a deep, neon rose-pink and 'Zuni' is a bright purple with a tinge of pink. ('Acoma' Crepe Myrtles are also more cold hardy.) I've have two ‘Zuni' in my yard for three winters now and they come back each year.

I consider them small shrubs or even a large ground cover. I cut mine back early every spring down to within 4" of the ground and the plants resprout from the base. They grow back quickly (mine right now are probably 18" tall) and will bloom spectacularly later on this summer.

It's disappointing to me that they won't get taller because I think that the bark of the trunk of these plants is one of their nicest attributes, but they usually won't winter here and die back to the ground unless they're placed in a very protected place.

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Question: My 20+ year old corkscrew willow is losing its bark and the branches are dying. Help!

Answer: This doesn't sound good for your Willow. Around here, the problem is usually a borer or a fungal disease (or even both). The common fungal disease here is called Cytospora Canker. It gets into the plant and kills off the vascular tissue "strangling" the plant. The unfortunate thing about it is that there's really nothing you can do to fight the disease other than keeping the tree as healthy and vigorous as possible. If you can get the tree turned around, it will sometimes fight off the disease. The problem is that once the tree has hit the stage you're describing, it's usually too late to do anything. Wish I had better news, but I'm afraid you're probably going to lose the tree.

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When is the best time to transplant natives such as Rabbitbrush, Sage, Greasewood and Yucca?  I would like to transplant some of these plants from another property to my home.  Please advise if there are any special needs any of these plants have while transplanting.

Answer: I think the best time to transplant these guys is early in the spring—mid to late March around here. I like to transplant just about all woody plants then. Doing it while they’re dormant reduces transplant shock and improves survivability. I also like to wait until winter’s just about done to do it. Winter can be a somewhat stressful time for plants and I like for the plants to get through that as strong as possible before transplanting. You can transplant them in the fall, but adding the stress of the transplanting with that of the winter sometimes adds up to die-back or even death of the plant. Another plus for doing it in March is that the plants will be breaking dormancy soon and will start healing up the damage done during the transplanting.

When you do the transplanting, first of all, don’t get too greedy! It’s tempting to dig up a big and full, mature plant, but the bigger the plant, the greater the chance of failure. Start with a smaller plant; your success rate will be better and they’ll grow fast anyway. Before you dig up the plant, be ready to plant them at home, you want to get the transplants back into the ground as quickly as possible. Dig them up with a nice big ball of soil around the roots. Of course it needs to be small enough for you to handle, but the bigger the rootball, the better your chances of success are. Keep the rootball intact. Breaking or cracking of the rootball will reduce your chances of success. Most people wrap the rootball with burlap or an old sheet to help support it and keep it intact. Get them planted in your yard, water them in well once, and after the water has soaked in, give them a second soaking with a solution of Fertilome Root Stimulator.

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I would like to know how to care for my hardy pampas and dwarf pampas grass for the winter. Also can the "feathers" be used for decoration in the home?

Answer: Taking care of any ornamental grass is pretty easy. The main thing you have to do is to cut the brown, dead foliage down sometime before spring. Many people leave the foliage on their plant through the winter as it adds some texture and interest to an otherwise bland winter landscape. However, if you want to get out in the yard and just get things cleaned up, it’s okay to cut the foliage back this fall. Just make sure that the foliage is dried up before you cut it back. If you decide to wait until next spring to do the cutting just be sure to do it early before the new shoots of grass begin to emerge. I’d figure on getting it done before the end of March. If the grass has started to sprout when you cut it back, you’ll cut off the tips of the new shoots and those cut ends will turn brown giving your grass an unkempt, ratty appearance (at least temporarily).

One trick in cutting back most ornamental grasses that I’ve learned is to tie up the foliage with some twine before cutting. You’ll end up with some funny-looking “pony tail” looking affairs. Tie the grass tightly so the bundle doesn’t fall apart. Then use a regular wood crosscut saw to cut the foliage off. You can use pruning shears, but it’s a lot of work and believe me, your hand will feel it when you’re done! The saw makes the job much easier and once it’s cut off, the old grass is already bundled up for disposal—no raking or cleanup needed.

The seed plumes are great to use in dried arrangements or other decorations. You may want to spray the plume with some spray acrylic to hold the plume together. If you don’t, the seeds can come off and make a mess.

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