Archive for the Ask MG department

Why won’t my hydrangeas bloom?

March 26, 2020 • Leave a Comment

I planted 2 Endless Summer hydrangeas and they bloomed beautifully. Over the next 2 years, I planted 4 more in a row next to the 2 originals, and they bloomed well. Last summer, however, the first two (which are 3 times the size of the last two) had beautiful, healthy foliage but absolutely no blooms. There were a couple of buds just forming in late August. Any suggestions to get the originals to bloom again this summer?

Endless Summer hydrangea (H. macrophylla) is a remontant (everblooming) variety. There is the initial late spring flush followed by sporadic blooming through the growing season. It blooms on both old and new wood growth. Wonderful attributes, if managed properly. In the North, these hydrangeas like full morning sun and afternoon shade from heat. Make sure the plants are getting about 5 to 6 hours of sun. Check that a tree or outbuilding isn’t shading them more than necessary.

Lack of bloom and robust foliage can indicate too much water and too much nitrogen-rich fertilizer. Check your watering practices. Water thoroughly but less frequently. They like rich, moist soil, but not saturated soil. A quality, slow-release granular fertilizer applied once in spring or early summer should suffice for these acid-lovers.

Be careful when and how much you prune. Don’t cut them back to the ground like the old-fashioned ‘Annabelle.’ Endless Summer does bloom on new wood, but if you severely prune them, you lose the benefit of old wood flower buds. The few buds you saw forming in August is how long it took the new wood to catch up. Review and adjust your maintenance practices, and you should have a better bloom season on the originals as well as the newer plantings.

Choosing drought-tolerant annuals

March 8, 2020 • Leave a Comment

Last summer we planted portulacas on a cemetery plot. Unfortunately, critters ate and pulled out the blooms. The cemetery requires annuals only. Could you suggest some other flowers we could use that are critter proof and will do well in full sun and with limited watering.

Moss roses (Portulaca) are drought tolerant since they have a taproot as well as surface roots, and their leaves and stems are able to store water. This drought tolerance makes them desirable to animals that are looking for a drink during a dry spell. Your moss roses were probably a tasty treat for the critters that helped themselves to them. A cemetery is a safe environment for animals that are nocturnal eaters, such as rabbits. The moss roses were a good choice for a cemetery if not for those pesky critters. There are some traits that may make plants less desirable to rabbits and deer, and those include strong odors and fuzzy leaves.

An annual is a plant that completes its life cycle in one season and, unlike perennials that can become drought tolerant after they are established, annuals do not have enough time for that process to occur. It is important to choose healthy plants from a reputable garden center so that you know they have been consistently watered and have a strong start. Plants that have been allowed to dry out while in pots or flats have been stressed and do not have the best chance of survival. Choose a disease-resistant variety and plant after all danger of frost has passed. Add some organic matter such as compost or manure to the soil when you are planting. Space your plants properly according to directions to allow air circulation around the plants to help prevent disease. Consistent watering is important for the first month. If Mother Nature doesn’t provide it, you may want to. Deadheading spent blooms, if necessary, and fertilizing according to plant needs will keep them producing blooms throughout the season.

Some choices to consider that are drought-tolerant, like full sun, and may be less desirable to critters include: marigolds, pot marigolds (Calendula), celosia, cleome (there are some dwarf varieties that would be well suited to your site), cosmos, dusty miller, zinnia ‘Profusion,’ ageratum, wax begonia, and globe amaranth.

Tar spot on maple leaves

February 28, 2020 • Leave a Comment

Do the enclosed leaves come from diseased trees? There have been spots on the autumn leaves from these 2 trees for the last couple years, but not as many as last fall. They are the neighbor’s backyard trees, but the leaves fall into our yard. Are they dangerous to other growth or to the soil in our garden? The neighbor said if we wanted to have them cut down, he would not object.

The maple trees are infected with a fungus known as “tar spot” (Rhytisma acerinum). Many maple species are host to the fungus which is readily visible and, therefore, one of the easiest maple diseases to diagnose. Fortunately, it is one of the least damaging ailments on its host. It can cause early leaf drop but does not cause serious harm to established trees.

The tar-like spot is a fruiting structure of the fungus that survives the winter on fallen leaves. The following spring, just as new leaves are unfolding, the fungal tissue in the leaves on the ground ripens. The surfaces of the spots split and minute, needle-like spores escape. The spores are carried by the wind and, if they land on new leaves of a susceptible host, they may germinate, penetrate the leaf tissue, and start a new disease cycle.

Tar spot will not affect your soil health. Fungi are host specific and this fungus will only affect maple and sycamore trees. The most effective management practice is to rake and destroy the infected leaves in the fall. This will reduce the number of overwintering “spots” (fungal reproductive structures) that can produce spores the following spring. An almost as effective alternative is to mulch the leaves. But the mulch pile should be covered or turned before new leaves begin to emerge in the spring in order to destroy many of the spores before they mature.

What is quite interesting is that the apparent absence of the fungus in urban areas and abundance in rural areas has led to its use as a biological indicator of air pollution. Researchers think the absence in urban areas is caused by the amount of sulfur dioxide (exhausted by combustion engines) in the air.

Preferred growing conditions for redbuds

February 24, 2020 • Leave a Comment

I bought a 4-foot tall redbud and it has not grown at all. It leafs out, blooms for spring, then it looks dead by mid-August. Maybe it has verticillium wilt? Does this come back every year? If so, how do I prevent it?

Eastern redbud (Cercis canadensis) is highly valued in the urban landscape for its pink spring flowers and its smaller, manageable size. As an understory tree, it prefers moist, well-drained, deep soils. It tolerates various soil types, except those that are permanently wet, and adapts to full sun or light shade. Regular watering and fertilizing are keys to keeping it vigorous. Unfortunately, it suffers dramatically from lack of water, too much water, or mechanical injury.

Since your redbud does bloom and leaf out in spring, but looks dead by mid-August, your tree may be responding to inconsistent water patterns. There is plenty of moisture available in spring, from snowmelt and rain. By the apex of summer heat, the redbud may be packing all its energy into saving moisture for survival by dropping leaves and going dormant. This is not the typical pattern of a tree suffering from the soil-borne fungus verticillium wilt, which is incurable and progresses over time until the tree is dead.

Before assuming your redbud has this disease, consider the soil conditions where you planted it and your maintenance practices. Is the tree in the middle of lawn, competing with turf up to its trunk for moisture and nutrients? Is it subject to potential mowing damage? Has it ever received a slow-release granular fertilizer beyond its nursery container? Does it get regular deep watering during periods of no rain? With conscientious adjustments to maintenance and amendments, you strengthen your redbud’s ability to withstand such diseases as verticillium wilt, canker, and even insect pests.

With the new growing season upon us, re-examine your plant maintenance routine and strategize a consistent watering program as well as a spring and fall granular fertilizer application. If your tree is sited in lawn, remove the turf away from the trunk out to the tree’s drip line so the root zone has an equal chance for water. The redbud likes moist (not soggy) soil that is well-drained and rich, medium sunlight, and fertilizer to replenish what was used from its original container. Be observant about the tree’s progress through the season, and you may get to enjoy your redbud’s lovely yellow fall display.

Can vegetable gardens be planted near or over septic fields?

July 27, 2019 • Leave a Comment

Our vegetable garden is over part of our septic field. This is the only part of our yard that gets enough sun. Can there be a problem with possible contamination?

There can be a problem with contamination. Unless your septic tank is completely self-contained and does not permeate into the soil, there are health concerns. Most governmental units have mandated households to convert to self-contained systems to protect Michigan’s groundwater from contamination.

Septic effluent contains chemicals and pathogens potentially harmful to people, animals or plants. Soil types affect how a septic system behaves. Clay soils release cleared effluent in a few inches. However clay does not percolate or drain well and is not a good choice for a septic site in general. Sandy soils permit greater travel of effluent and pathogens, because they drain so quickly. In that case, contaminants can travel greater distances.

Root crops such as carrots or potatoes, which grow in the soil, are likely to pick up pathogens from effluent in the soil over, next to, or downhill from drain field trenches. Leafy crops like lettuce or broccoli that develop above ground may be contaminated by pathogens that splash up from the soil surface during watering or a rainfall. Above ground crops like those that vine (cucumbers, tomatoes, peppers), are less likely to be affected by splash up since they grow vertically out of the way. Homes where water is “hard” and which use a salt-based water softener system are more apt to be passing high levels of brine into the septic drain field. These salts can damage plants that grow nearby.

As septic effluent drains out into the lines, it is filtered slowly through the soil. Beneficial soil microbes digest harmful bacteria and viruses. While septic systems are designed to prevent disease-causing soil contamination, there is no easy way to know if your system is functioning properly. In addition to bacteria, consider all the household chemicals that go down your drains every day. Plants are by nature absorbing and processing “factories,” cleaning up the environment. All of this can end up in those vegetables you planted in the only sunny part of your yard.

What is causing purple leaf color on vines?

July 22, 2019 • Leave a Comment

I recently planted several vines in containers in full sun as directed. Now I’ve noticed the leaves appear to have a purple cast to them. What might be wrong?

Signs of stress caused by improper pot size, insufficient nutrients, soil, water, weather conditions, site incompatibilities or drainage can by themselves, or in combination, cause color change in plant leaves. Some plants with dark green leaves that are prone to leaf burn can develop color changes in their leaves if they are receiving too much light. The opposite is also true if they do not receive adequate light. Then again there are plants that have naturally occurring color changes in their leaves and the color is not indicative of a plant problem. With the wide selection of hybrids available, it is not a surprise that we find it difficult to figure out if the coloring is genetic or not.

Annual and perennial vines are easy-to-grow plants if you have a basic knowledge of their cultural needs. Some key facts pertaining to raising vines in your garden: Select varieties that will thrive, not just survive, in the garden. Site conditions to consider include light, water, weather and soil. Most vines like well-drained, organic-rich soil that will support their fast growth rate. Once the vine develops a good root system, stress will be kept to a minimum. Container-grown plants should be watered and fed regularly with a balanced fertilizer. Don’t postpone installing the vine’s support system; they love to hold on. Mulch helps to keep in moisture and cool the root system. Pruning should include removal of diseased or damaged stems. A perennial vine requires removal of dense, tangled growth to allow air flow for healthy growth, while annual vines require little pruning except for shaping.

False indigo growing tips

June 27, 2019 • Leave a Comment

I have 4 false indigos (Baptisia) by my house that were doing great some years ago, but now are very leggy and die off by midsummer. I have 4 other ones near a large pine tree that look magnificent. The ones by my house used to look this way. These plants have been here since we moved into our house 15 years ago. Is there anything I can do to get them back to their full size?

There are two clues in your Baptisia predicament. The first hint is the four plants “near a large pine tree” are magnificent. The second hint is the plants by the house “have been there since you moved in 15 years ago.”

False indigo wants full sun for best performance. Although they like rich soils, they are very tolerant of poor soil and arid conditions, which is what they have around the large pine tree. Since the ones by your house used to look that way, it’s possible a matured tree canopy now diminishes access to full sun. In shade, false indigo gets leggy and needs to be staked. They also spread by rhizomes out from the main base and can consume considerable garden space. Your false indigos have that elbow room out at the pine. The false indigo next to your house may have used up all the space they had available in 15 years, particularly if they are confined by a house foundation and a nearby concrete walk or driveway. There’s no place for them to go.

Since we are moving into the heat of summer, wait until fall to cut back and dig up the false indigos along your house and divide them. Replenish and amend the soil in the area and transplant a limited number of small divisions back to this area. If examining the overhead tree canopy reveals access to full sun is compromised, you can plan to stake the transplanted divisions or simply add them to the great crop you have growing out by the pine.

Choosing plants for hedges

June 22, 2019 • Leave a Comment

I would like to create a formal English garden look, where “squared-off” hedges line the garden perimeter. Can you recommend hedge plant options (other than yews) that grow at least 4 to 8 feet tall, look thick and full (like a solid wall), and grow in sun and shade?

You have several restrictions in your plant request that limit your choices. Your height requirement creates a problem for boxwood (Buxus sempervirens), a favorite of formal English hedges, because they are a rather slow grower. However, they hold the geometric pruning well, are sun and shade tolerant, and form a dense thicket of glossy leaves. Boxwoods are the choice for knot gardens, parterres and topiaries because they are evergreen and hold a crisp line when pruned.

Privet (Ligustrum amurense) grows quickly, is easily sheared to shape and can reach your desired height. It is also tolerant of light and soil variations. Unfortunately, in zones 3 to 7, it is considered deciduous, even though its dense twiggy nature is a screening element in itself.

Since the perimeter of the garden is the designated planting zone, you might consider Japanese holly (Ilex crenata), which is very shearable and has a medium growth rate. Their leaves are spiny but lustrous. They will tolerate full to part sun, but need somewhat acid (low pH) soil and good drainage with sustained moisture. The downside is that they need protection from drought and wind.

There are few if any pines or spruces that meet your criteria. However, the workhorse of the residential landscape, the columnar American arborvitae (Thuja occidentalis), may suit them all. The varieties ‘Emerald’ and ‘Techny’ both meet your height requirement of 4 to 8 feet. They hold their color in winter, and have considerable heat and light tolerance. Shearing and pruning them before spring growth will keep them full and dense. They have a natural pyramidal tendency, but can be nicely shaped to be wider at the base, to give the “squared-off” hedge look you are striving for. Keeping them slightly wider at the base allows light to reach the interior of the shrub, allowing active new growth and preventing thinning of the interior.

Growing grass under trees

June 18, 2019 • Leave a Comment

Our yard is shaded by oaks. We overseed every year with shady grass mix. But by the next spring most of the grass has died. What can we do to grow grass in this situation?

You have a couple of choices. You can continue the frustrating cycle of growing grass, or take an alternative approach to living with your oaks. Turf grass needs sun to germinate and establish a root system, even if it is the “shady grass mix.” If your oak canopy is heavy and dense, you could have the canopy judiciously thinned by a trained arborist. They will prune when the trees are dormant in winter and there is little chance for them to be infected with the oak wilt disease. This might open up the canopy enough to let the turf lawn get established.

However, you should know that oak trees can take up to 50 gallons or more of water a day. So while you are watering that lawn you’ve overseeded, the oak trees with their extensive root systems are enjoying the feast. The turf grass never gets its root system established because the oaks are not only shading it out, but also absorbing most of the water.

This is not necessarily a bad thing. Oak trees are preferable bastions of shade. The alternative is to try a different groundcover that isn’t lawn. Oak trees create dry shade. It sounds like your lawn is fairly thin underneath them, which is why you keep overseeding every year. Why not plant dry shade-loving perennials? There are a number of low maintenance plants that would not only lend interest to the landscape under the oak trees, but are low profile, will come up every year, will succeed where turf grass fails, and will provide “green coverage” that you don’t even have to mow.

Consider a mass planting of variegated hostas that would “light up” the shady area under the canopy. Another perennial often used where grass is unsuccessful is lily turf (Liriope spicata). It even looks like grass, but has the bonus of a purple-blue flower in summer, which turns to a red-brown berry in fall. At the outer edge or drip line of the canopy, you could mass plant Stella d’Oro daylilies. They tolerate a wide range of soil types and light conditions. Their yellow blooms are continuously cheerful and when finally done blooming, their foliage lasts until frost. A simple ground-hugging vine is vinca, sometimes called myrtle. It produces a lovely blue flower in spring that shows well in heavy shade. There is also the nice spotted dead nettle (Lamium maculatum) with its silver and green mottled leaves. The cultivar ‘White Nancy’ produces a lovely white flower while other varieties produce pink blossoms mid-spring.

So there are several alternatives and choices to groundcovers that aren’t turf grasses. You need to decide where to put your money: into perennials that will succeed in the shade of your mighty oaks, or continue trying to grow turf grass that will always struggle.

Planting ideas for ditches and swampy areas

April 15, 2019 • Leave a Comment

After a moderate rain, water collects in a shallow ditch at the back of my lawn. It looks swampy every year. Any design/planting ideas to improve the look of this area?

This unfortunate nuisance that often occurs in both old and new landscapes is actually a garden opportunity. Evaluate the square footage involved and consider putting in a rain garden. Very simply, a rain garden is a planted depression that allows rainwater runoff from impervious urban areas like roofs, driveways, walkways, and compacted lawn areas the opportunity to be absorbed. It reduces rain runoff by allowing storm water to soak into the ground (as opposed to flowing into drains and surface waters, which causes erosion, water pollution and flooding).

Usually, it is a small garden that is designed to withstand the extremes of moisture and concentrations of nutrients, particularly nitrogen and phosphorus often found in storm water runoff. A rain garden retards the water flow and absorption, allowing more time to infiltrate and less opportunity to gain momentum and erosive power. Because this area is in your lawn, you have the opportunity to prepare an area with select trees and shrubs as well as perennials that will enjoy absorbing and utilizing that rainwater, processing it, and creating an entire ecosystem beneficial to the greater good of the landscape.

The Wisconsin Department of Natural Resources has a 32-page online manual for the how-tos of constructing a rain garden, from measuring to digging to planting. They even include several design diagrams. The basic information is excellent, but it does focus on downspout and house foundation locations for the most part.

The key for an area like yours (away from a downspout) is to use tree and shrub species that love wet conditions. There are a number of Michigan native plants that suit the criteria well. Because you are not necessarily restricted by the proximity of a building, you can consider using trees like river birch (Betula nigra ‘Heritage’), which has the grace of a willow but none of the mess. It also has excellent winter interest in its buff pink, exfoliating bark.

Consider planting a cluster of red and yellow twig dogwood shrubs (Cornus sericea ‘Alba’ and Cornus sericea ‘Flaviramea’). These shrubs are especially suited to swampy areas and, with their colorful twigs exposed in Michigan winters, become a highlight of the snow-filled landscape. Depending on how large your ditch is, you could possibly add a smaller ornamental tree such as a native witch hazel (Hamamelis virginiana), which blooms in October and November, or a native shrub such as the common elderberry (Sambucus canadensis) whose fall fruit provides a great food source for both birds and animals.

Planting a rain garden is a very eco-friendly way to deal with standing water and provide assistance to the natural filtration process for our groundwater. You not only solve the drainage problem but also turn an eyesore into a work of beauty.

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