“Sauntering along and admiring people’s front yard is a lot less common in the US than Europe.” The reverse is the case with owning firearms – but Beumer was undeterred. “The friends I stayed with were worried about me,” she laughs. “But some people saw me looking at their front yard and when I explained what I was doing, they invited me in to show me their garden as well.”

A desert city so fond of green? “When the settlers moved to Arizona, they took the idea of lush, green European gardens with them.” The discrepancy between that displaced ideal and one of the hottest cities in the US has obvious consequences. “Irrigating the gardens makes up 70% of household water consumption. A lot of the water from the sprinklers evaporates before it touches the lawn.”

Taking her newly discovered curiosity for other people’s gardens back home led to a grey revelation. “Here it was the opposite: more and more people are paving their gardens.” The low-maintenance look isn’t only due to the Dutch being intensely and amiably practical. “They are setting up outdoor kitchens and lounge areas. That trend is pushed by TV programmes promoting gardens as extended living rooms.” 

It’s a personal choice which, on aggregate, has public consequences. “Urban heat islands can be up to 10 degrees hotter than the surrounding areas.” The main reason being surface modifications: pavement. Built up cities store heat – green spaces offset the effect somewhat. “A single tree in your garden is the equivalent of 10 air conditioning units.”

It’s not a fair-weather problem either. Paved gardens mean that rainwater isn’t absorbed and stored in the soil; instead it flows directly into the sewage systems. The excess burden leads to flooded basements and diminished groundwater supplies. Also: in general, people like it green. “It’s funny: people want green public spaces, while at the same time choosing a paved garden…”

The topic also occupies her outside of work – in the absence of a garden of her own, she’s turned to activism. Beumer is one of the founders of a nationwide initiative Operatie Steenbreek, a nationwide inititative named after Saxifrage or rock foil. It’s a network of several municipalities and knowledge institutions across the Netherlands that tries to promote greener cities.

“Connected gardens have tremendous public value but it’s difficult: people might not want to have a green garden – or might want to but don’t have the time.” She rejects taxing paved gardens as uncomfortably paternalistic. Instead, Operatie Steenbreek is trying different ways of approaching residents in different places - there are now more than a hundred cities participating.

Maastricht could be greener

They offer workshops and inspiration for lush but low maintenance gardens with e.g. ground cover, like vines, shrubs or moss. “You don’t have to do anything really; just put them there and cut them once a year. It keeps the soil healthy and it’s good for biodiversity because it shelters hedgehogs, birds and bugs.” Beumer thinks Maastricht has some catching up to do but sees plenty possibilities.

“You could think of pairing students who like gardening with older people with gardens who no longer can.” At the same time she acknowledges that a lot of good things are happening, from the redevelopment of the Tapijnkazerne to UM’s own sustainability efforts. Still, she prefers thinking big: “For example, you could green all the flat roofs on the Randwyck campus!”

As a scientist, Beumer takes a nuanced view on gardening. “You can get injured gardening or get diseases… or get annoyed by birds singing in the morning. It’s all about perception!” In the wetter areas, e.g. in Almere, there are mosquito issues, which a warming climate could exacerbate” At the same time, gardens, especially if they are connected, provide a habitat for many animals that eat mosquitos.

The benefits of having a green garden aren’t limited to biodiversity either. Beumer cites stress reduction as a major physical upside. Despite her critical and holistic approach, she remains a big fan of gardens. “I love doing the research! It’s fascinating: the gardens are as different as the people – even the completely paved ones are really diverse…”