Gardeners who thought they were giving a helpful boost to their local bee populations by planting “bee friendly” gardens may in fact be doing more harm than good, according to a new study released today.

Environmental groups Friends of the Earth-US and the Pesticide Research Institute tested a small sample of plants purchased from Lowe’s, Home Depot, and Orchard Supply Hardware (which is currently being acquired by Lowe’s), and found that just over half of the plants had been pre-treated with pesticides that they say are known to kill bees.

“The pilot study confirms that many of the plants sold in nurseries and garden stores across the U.S. have been pre-treated with systemic neonicotinoid insecticides, making them potentially toxic to pollinators,” said Timothy Brown, co-author of the study and associate scientist with the Pesticide Research Institute.

Thirteen samples were purchased in the San Francisco Bay area, the Washington, D.C. area and in Minneapolis, and were made up of soft-stemmed flowering plants known to attract both bees and pest insects like aphids. The plants included squash, tomato, pumpkin, zinnia, daisy, salvia and gaillardia.

Of the samples tested, the tomato plant purchased in California had the highest concentration of pesticide.

Stephen Holmes, a spokesperson with Home Depot, says they haven’t yet reviewed the study. “But the importance of the bee population is something we take very seriously, so we’ll be reaching out to the study groups to learn more.”

Lowe’s did not respond to our request for an interview.

Bayer Crop Science said in an email that they have not seen the report, and cannot comment on its scientific merit, “except to say that extensive research has shown that neonicotinoids are not responsible for honey bee colony decline.”

“The fact that residues of a registered product were allegedly found in some ornamental plants does not mean that honey bees were exposed to them, nor does it indicate causation for colony decline, which most experts attribute to a number of factors, including parasites, diseases, nutritional deficiencies, beekeeping practices and loss of habitat,” adds Bayer spokesperson Becca Hogan.

It’s a stance the company also took when they launched a controversial “bee tour” last spring, and on its “Bee Care” website, which claims that bee losses are not a new phenomenon, and that the “overall number of honey bee colonies worldwide has increased by some 45 percent over the last 50 years, not decreased.”

The European Union disagrees, and is expected to suspend the use of three neonic pesticides later this year, after an earlier study identified risks to bees exposed to the insecticides.

There’s plenty of skeptisism here at home too. Last month lawmakers introduced the Save America’s Pollinators Act, which would direct the EPA to “suspend use of the most bee-toxic neonicotinoids for use in seed treatment, soil application, or foliar treatment on bee attractive plants within 180 days, and to review these neonicotinoids and make a new determination about their proper application and safe use.”

Why is this class of pesticides getting such scrutiny?

As we told you earlier this spring, unlike older pesticides, neonicotinoids are typically applied to seeds before planting crops like corn and soybeans. It’s then taken up through the vascular system of the plant and expressed through the pollen and nectar, which bees rely on for food. (Bees aren’t the only worry. There are also serious concerns that neonicotinoids are harming birds and aquatic life as well.)

According to Paul Towers, spokesperson for the Pesticide Action Network, the introduction of neonicotinoids onto farms in the mid-2000s coincides with more widespread bee-colony collapses than had been seen before. The group has filed a lawsuit with the Environmental Protection Agency to curb the widespread use of the pesticide.

The new study comes with plenty of recommendations for keeping bees safe, aimed at everyone from garden retailers to municipalities to consumers. They include stopping the use of all neonicotinoids on landscaping plants, and a call for stores to stop offering pesticides like Merit or Meridian on store shelves.

“This is just a snapshot of how the pesticides are being used in home garden plants,” says Brown. “But I think it’s a really important study for people to be aware of when they plan out their gardens next season, and we hope the retailers will take some action on this.”

On a muggy Thursday afternoon, a trio of tourists walking through the Garden District stopped on the sidewalk in front of a grand house on Washington Avenue. They peered over the fence, getting a furtive glance at the garden.

On a quick look — say from the front seat of a car zooming down busy Washington Avenue — it’s easy to miss the elegant parterre that stretches across the side yard of the house, an 1855 masterpiece designed by New Orleans’ most famous 19th century architect, James Gallier, and commissioned by James Robb, a prominent businessmen of the time. But from the sidewalk you can get a partial view of the magnificent yard.

Behind the hedges

THE GARDEN: A formal parterre in front and a lushly landscaped pool and patio in the back of a Garden District house

THE OWNERS: Cherie and Jonathan Thompson

THE DETAILS: Though the Thompsons started from scratch when they renovated the yards, the formal front garden mirrors a design that has been part of the 1855 House for at least two decades, if not longer. Symmetrical beds feature cone and sphere-shaped boxwoods, two espaliered European olive trees and a fountain the couple had moved from their previous home, creating a majestic — and meticulously manicured — space

WHY THEY LOVE IT: “I love shapely boxwoods. I just think they’re fun,” Cherie Thompson said. “Along the wall in the backyard are (Miami Supreme) gardenias. They’re so fragrant they just fill the air when they’re in bloom.”

The landscape is half hidden behind a close-clipped hedge of Japanese yew. It’s not exactly a secret garden, but it has a storybook air — somewhere you’d expect to see a princess, perhaps — when you peek behind the hedge and see the circular brick paths, tidy trimmed boxwoods and tiered fountain, its trickling water providing a natural soundtrack.

Parterres are painstakingly disciplined gardens. The tradition of planting beds in puzzle-like patterns and ornamental shapes became popular in 17th century Europe, where it was de rigueur for royal estates. The sophisticated style, according to several landscaping sources, grew out of medieval knot gardens, which separated plants from each other by small hedges.

Cherie and Jonathan Thompson love the symmetry of the classic design and found it fitting for the stately Garden District home they bought in 2007. Before moving in, the couple began a cosmetic renovation of the house, but also turned their attention to the landscape. The 5,000-square-foot home had few views of the garden, a problem the couple solved by adding additional windows.

A parterre was already in place in front, but the bricks were pulling up and it needed refurbishing. The backyard was dominated by a series of space-consuming sago palms (which, despite their common name, aren’t palms, but cycads.) The Thompsons decide a swimming pool would be preferable to the spiky sagos.

The couple engaged landscape architect Rene J.L. Fransen to design the yard, which now maintains its formality but provides a refuge for relaxation for the couple and their 10-month-old daughter, Claire.

Many old New Orleans houses traditionally featured formal gardens, Fransen said, though, it’s unknown if this house’s first owner planted one. The front parterre has been in place at least for two decades, if not longer.

The gardens of historic New Orleans homes often “had a rigid formality to the beds, but they had vegetables and fruit trees and things like that in them,” Fransen said. “They didn’t have free-form beds, but, because of the nature of the climate, the gardens weren’t formal because things grew like wild.”

In the Thompsons’ yard, Fransen pulled up the parterre’s bricks and re-laid them. The brick paths define the garden’s geometry as do neatly planted needlepoint hollies and Japanese yews. Shaped boxwoods, not a leaf out of place, are living finials, sprouting from the center of the beds.

The fountain, which was a beloved item from the couple’s previous home in the Irish Channel, became the centerpiece of the space, replacing a previous fountain that had been in the Garden District yard.

“It’s supposed to have koi in it,” Jonathan said, passing the fountain as he unlocked the gate that leads from the front to the backyard. “But right now, it just has a turtle.”

The wall and gate that borders the front garden was moved and rebuilt to make more room for the backyard. The gate opens to a slender pool and spacious patio. Traditional elements — New York red flagstone laid out in a diamond pattern, a large, urn-shaped fountain and Bevolo lights — echo the formality of the front yard, while lush gardens, framed by a green wall of Japanese blueberry trees, make it feel relaxed enough for hanging out.

“This pool comfortably seats 20 people,” said Cherie, who proved that statement during one of the couple’s outdoor parties. The pool’s long, narrow design also makes it good for lap swimming.

The Thompsons hired NOLA + Design, a landscape company owned by Aaron Adolph and Jonathan Steudlein, to handle the planting and maintenance for the entire property.

A pair of navel orange trees, loaded with still-green fruit, now flank the steps to the pool, while planters and beds are filled with blue plumbago, giant walking iris, dwarf white Robin Hill azaleas and a Japanese red maple.

One of the yard’s showpiece plants is an Anderson crepe hibiscus, with pale pink flowers and dark green foliage, trained to grow up a custom ironwork arch separating the driveway from pool area.

A covered patio is the place where the couple likes to sit with their coffee on weekend mornings and unwind with a glass of wine after a workday; Jonathan is in the film industry and Cherie is an accountant for a local non-profit.

Around the yard are two bronze statues — Lazarus and Isadora — both by Folsom sculptor William Binnings, Cherie’s uncle. “I have loved that statue (of Lazarus) for years,” she said.

The yard provides plenty of room for entertaining, with tables and outdoor seating, including a tiny iron and wood bistro set, shrunk down to child’s size. Cherie got it on her third birthday, and her parents held onto it even after she grew up.

When the Thompsons had Claire, Cherie’s parents gave the set to them, and Jonathan refinished it, adding a fresh coat of white paint. It now looks ready to host a new generation of tiny tea parties.

“This is another living room,” Cherie said. “It’s where we relax.”

Green roofing – the practice of planting vegetation on a building’s roof or terrace – is the ultimate in urban landscaping, making the most of extremely limited space to bring a flash of greenery to a cityscape.

For inmidtown, the Business Improvement District for Bloomsbury, Holborn and St Giles, it’s about more than making London’s roofs easy on the eye though.

The business benefits are significant, yet largely untapped. From improved employee engagement and productivity; to reduced carbon emissions, green roofs could save businesses millions in energy costs. They can improve a property’s value too, and even reduce noise entering the building.

The environmental benefits are just as clear. In addition to improving insulation and thereby reducing carbon emissions and energy costs, they’re an intelligent solution for businesses that hich want to adapt to climate change, which means that rainfall bursts will become shorter but more intensive, especially in summer.

Green roofs can help to contain flash flooding and improve the quality of water run-off, with Environment Agency research noting that both nitrogen and phosphorus can be reduced through green roofs. Furthermore, green roofs provide a habitat for wildlife, support the local environment by helping to lower urban air temperatures, and improve air quality. Growing fruit and vegetables, which can be used by businesses to supplement produce they buy, is the latest evolution of London’s green roofs.

As part of inmidtown’s bid to make the area London’s most sustainable commercial district, it recently launched two organic fruit and vegetable edible gardens across central London businesses. In addition to the host of environmental benefits already discussed, these gardens support hyper-local production of produce, and enable businesses to reduce the food miles associated with their usual orders, so offer yet another incentive.

The green roofs scheme is currently supported by organisations in the area such as law firm Olswang, and the Bloomsbury Street Hotel, which are growing edible roof gardens, whilst on a further two green roofs, law firm Mischon de Reya and the Trade Union Congress are growing wildflowers to support the local bee population.

The Bloomsbury Street Hotel, before and after. Photograph: inmidtown

The amount of upkeep needed for these roofs is minimal. The companies have established gardening clubs to maintain them, which are great for employee engagement too. Olswang’s gardening club not only ensures that employees can take a proper lunch break, but also that people from different areas of the business mix together. A gardening club offers an ideal, organic, opportunity for staff from all areas of the business to unite for a common goal.

Green roofs provide a good place to pop outside for a quick break for hard-working employees, and are also great for client entertainment. Olswang gave clients honey produced by its own bees last Christmas. The inmidtown Urban Bee Project encourages local businesses to give homes to hives and provide small areas of forage in the area for bees, another component to its bid to make the area London’s most sustainable commercial district.

The process of installing green roofs is streamlined, all the businesses involved in the scheme use pocket habitats, which are a series of small modular sacks filled with soil and planted. This is a far tidier, cheaper and quicker method than planting a full roof, and has the added benefit of providing form and structure to an area.

Each pocket habitat is an independent unit composed of variously textured and coloured recycled substrates and wildflower seed. The composite felt material is specifically engineered to optimise drainage to ensure plants do not become waterlogged. Drainage is a key function of green roofs – inmidtown’s project was partly funded by a £15,000 grant from Drain London, and the five roofs alone will re-use nearly 87,000l of rainwater.

Furthermore, pocket habitats can be tessellated to create mosaic that specifically allows for biodiversity. They are also easily portable, which is ideal for our roofs growing vegetables, as these can be seasonally harvested and then re-used.

Green roofs are a crucial development for London’s businesses, if we want to create and promote ourselves as a low-carbon city and a global leader in sustainability. Utilising the collective strength of its members, the inmidtown BID aims to establish an effective and practical model that can, and with any luck will, be replicated across the city.

Tass Mavrogordato is CEO of inmidtown, the Business Improvement District for Bloomsbury, Holborn and St Giles