On the grounds that if you are going to get wet, you might as well get muddy, I’ve been working in the teeming rain on the bog garden by the pond. Given the amount of rain the British Isles have had this summer, I imagine a few people may be contemplating starting a bog garden. So I thought I’d go back to a few first principles – learned through hard experience. If you also want a professional gardener’s guidance (plus an excellent plant list) I thoroughly recommend Beth Chatto’s ‘The Damp Garden’ – a book that helped me hugely when I was starting to learn about bogs.
It’s no good just finding a wet patch and sticking plants into it. It’s important to know where the water is coming from, where it is going to, and whether there is any flow through the soil. Plants will die if their roots hit the anaerobic environment of stagnant water.
Other than the purely aquatic ones, only a few plants will tolerate waterlogging for any length of time. The primulas here regularly get flooded, but there’s a drain to one side, so the surface water soon disappears. Ideally, you want the water table to be around about a foot (50/60 cms) beneath the soil surface.
The quickest way to explore what the water is doing beneath your boggy patch is to dig a hole, watch how quickly it fills, whether the level varies much, and whether the soil at the bottom remains damp during a dry spell. Fill the hole to the brim with a bucket of water and see how fast it sinks back to the previous level. If it lingers longer than few hours, you probably need to improve the drainage. Here’s a place (it’s supposed to be a path) where a new drain is definitely needed:
If it’s not clear where your water is flowing to, one solution is to create a soakaway at the lowest point of your bog. Dig as deep a hole as you can manage, drop in a layer of rubble, and then fill it with gravel. Then direct your drainage into it. I always leave my drains open. In my experience, no terra cotta or plastic pipe can cope with very fine clay silt or with primula roots, and digging up buried drains is a far worse task than clearing open ones. I dealt with constructing an open drain here, and in subsequent posts, and I’m at work leading further seepage directly into it.
You need to be able to get to the interior of your bog garden without sinking into the ooze, especially if you take a wheelbarrow. Compacting damp soil by treading on it constantly does no one any favours. So a path of some hard material is probably needed, preferably stones or bricks – on end – .Gravel just sinks into the mud, and if you use slabs and drop one in the wrong place on sticky clay, it’s the devil’s own job to shift it. From an aesthetic standpoint, your path should appear to have (or have had) a function other than just leading you into a bog. I try to disguise mine as a rock shelf.
Weeding a bog garden is the pits, and to be avoided at all costs. This means choosing plants which are big enough to dominate buttercups and other damp-loving weeds. It also means avoiding small damp-loving plants. This is a sacrifice, but believe me, in the long term, you won’t regret it. Your plants may look nice and manageable in Spring, but by August you will be deep in the wet foliage trying to save your prize specimens from the rampant jungle. Big is best. And, iIf you have enough space for it, gunnera tinctoria takes on everything around it and wins.
Otherwise, I rely on the ligularia and inula families, plus the big rogersias, and tough, rampant hostas. Iris too, of course. Even the semi-wild montbretia, crocosmia x crocosmiflora is happy in a wet soil and forms huge clumps that suppress any intruders. More refined crocosmia cultivars aren’t robust enough .
But of course, the star of my bog garden, seeding itself everywhere, and totally weed-proof is primula florindae, just now coming into the full glory of its flowering, its heady perfume at its best in the rain.