Some people love gardens a whole lot more than they love gardening. Those are the people gravel gardens are made for.
Gravel gardens are low-maintenance beds filled with drought-tolerant plants and covered with a thick layer of gravel that gives weeds nowhere to take hold. Once they're established, they require little upkeep except for a thorough cleanup in the spring and perhaps in autumn too.
Horticulturist Jeff Epping is so sold on the concept that he called it "one of my recent passions in gardening."
"All in all, it's pretty maintenance-friendly. Never say maintenance-free," he said with a laugh. Epping is director of horticulture at Olbrich Botanical Gardens in Wisconsin, which will soon plant its fourth gravel garden.
Its first was installed a few years ago with help from Roy Diblik, a nursery owner who had seen the concept at Hermannshof Garden in Germany and had installed one at his Northwind Perennial Farms.
Gravel gardens gained some popularity after noted British gardener Beth Chatto installed one starting in 1991 on what had been a compacted parking area. Her book Beth Chatto's Gravel Garden describes the garden and its creation and lists the plants she grows there.
Epping said a gravel garden works well for plants native to areas with well-drained soils that don't contain a lot of organic matter - sites such as rocky seaside areas. He especially likes using the gardens to grow flowering bulbs, which can rot in heavier soil.
Diblik, however, is experimenting with all kinds of plants in his gravel garden. "I'm going to try everything," he said. This isn't just a garden with gravel used as mulch. The pebble layer in a gravel garden is much thicker - about 10 to 12 centimetres - and serves as part of the plants' growing medium.
Keeping soil and plant debris out of the gravel is critical, which is why Akron garden designer Sabrena Schweyer believes gravel gardens are best installed by professionals or knowledgeable gardeners. If soil gets mixed into the gravel, or if leaves and other debris are left to decompose in it, weed seeds can sprout, said Schweyer, one of the principals of Salsbury-Schweyer Inc., a garden design and development firm.
That means once a gravel garden is planted, it can't be altered. No moving plants around. No dividing perennials. No adding annuals in the spring or mums in the autumn.
The idea is not to disturb the soil beneath the gravel, so the two don't get mixed together, Diblik said. That's why he thinks gravel gardens are ill-suited for people who like puttering in their gardens, but ideal for purposes such as lawn alternatives and parking lot landscaping.
"It's not for gardening," he said, "It's for taking up space in a more interesting way." A gravel garden needs to be installed in a fairly sunny site over soil that's at least 60 to 90 centimetres deep. The soil needs to drain well enough that it doesn't leave areas of standing water during rainy times, Diblik said.
The soil is topped with an even layer of gravel, 10 to 12 centimetres deep. At that depth, any weed seeds that might germinate can't send down tap roots deep enough or fast enough for the weeds to get established, Diblik explained. Epping said the garden needs to be contained by an edging so the gravel can be maintained at a consistent depth.
It's important that the gravel layer doesn't taper off at the edges of the bed, he said, because weeds can take hold in a shallower layer of stone. The gravel needs to be igneous or metamorphic rock, which won't break down over time, Epping said. It also needs to be fairly even in size, so it won't compact. He said Olbrich likes to use washed granite or quartzite chips that are about one cm across.
To plant a gravel garden, you start with pot-grown plants with root balls that are about as tall as the gravel is deep. Epping has found quart-size pots work best.
You remove a plant from its pot, dig down into the gravel just far enough to place the plant atop the soil, and then push the gravel back into place around the root ball. Given time, the plant's roots will reach down into the soil to get the moisture and nutrients it needs, but the gravel will keep the plant's crown dry and healthy, Diblik explained.
Those vulnerable plants dry out quickly at first. So for eight to 10 weeks, a newly planted gravel garden needs to be watered religiously - daily or every other day, depending on the conditions, Diblik said. After about eight weeks, he said, you can give the plants a gentle tug to tell whether they're attached to the soil. Once they are, they no longer need such an intensive watering schedule.
Epping said his gravel gardens have still needed fairly frequent watering throughout their first year, and the second year only during dry periods. After that, the gardens haven't needed any more water than nature supplies.
Nor does a gravel garden need fertilising. As the plants naturally replenish their roots, the roots that die break down and keep the soil fed, Diblik said.
Besides, Epping noted that the kinds of plants best suited to gravel gardens don't like rich soil. The plants are spaced close together, so after a few years they grow large enough to form a mass that hides most of the gravel and shades the ground.
That way, Diblik said, even if a little bit of soil does get into the gravel as a result of frost heaving, weed seeds won't have the sunlight they need to sprout. Epping said weeds sometimes grow in the plants' crowns, but those are easy to remove.
The biggest maintenance demand, Epping said, comes from keeping the garden clean. Every spring the gardeners at Olbrich cut back the plants and remove all the debris carefully, using rakes and a leaf blower so nothing is left behind to decompose in the gravel.
The demands of cleanup are why garden designer Schweyer wouldn't locate a gravel garden in an area with a lot of trees, which are notorious for dropping debris such as leaves and seeds.
Still, Schweyer believes gravel gardens will become increasingly appealing around the world as climate change brings more extreme temperatures. "I just think it's a more resilient way of gardening," she said.
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