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low ground cover on poorly drained clay

Posted by metiman MA (zone 6) (My Page) on
Mon, Jun 4, 12 at 20:34

For my front yard, I need to establish a no-mow ground cover that grows no higher than 12". That is the guideline given to me by my town's weed enforcement officer. Yes, we have one! As long as it is a monoculture and not listed as a weed I can grow pretty much anything I want to a height of 12" in my front and side yards. Unofficially. Officially the weed police = God.

Currently there is no lawn. Just some weeds that have an uncanny resemblance to skunk cabbage, a bit of some kind of grass, a few remnants of some white clover I planted many years ago, and mostly mud. As soon as it stops raining here I plan to nuke everything with some newly generic glyphosate.

Every year I scrape the topsoil from my front yard to tame the weeds. What's left isn't very fertile. Even mint has trouble growing. I planted some chocolate mint last year and it hasn't grown at all. I have a clump of spearmint that grows but doesn't spread. The fact that a skunk cabbage-ish plant is my dominant weed and the fact that even a brief rain shower forms puddles which take more than 24 hours to be absorbed leads me to conclude that I have poor drainage. This seems to rule out all but a small fraction of ground cover options, leaving mostly semi-aquatics and an elite group of seriously tough customers who don't care what they grow in.

With poor drainage the topic of soil amendments or raised beds is sometimes brought up. I think either would be rather expensive. The soil is sufficiently hard that I can jump up and down on a sharp shovel and penetrate no more than a a few inches even when the ground is wet and that's if I'm lucky about where I put the shovel. I think amending it would be...challenging. The raised bed thing might be possible in the sense that I could maybe buy a truckload of loam and spread it around on top of the hard pack. I also still have the piles of topsoil that have accumulated. Unless I can manage to add a lot of soil I don't think it will be game changing and at the moment I'm not prepared to spend the money.

So assuming the conditions of hard, rocky, clay with poor drainage what are my options for a < 12" ground cover? One of the more obvious answers would seem to be Creeping Jenny (Lysimachia nummularia). It really does seem ideal. A more aquatic plant might deal better with poor drainage, but it also tends to be thirsty all the time, and I don't have a pond or stream in my front yard. If it hasn't rained for more than a week, the soil may get kind of dry. That's the problem with poor drainage. You really need a plant that is root rot and wet feet resistant but also drought resistant. Another option I considered is dwarf corkscrew rush (Juncus filiformus 'spiralis'). 9" height. Seeds are available for it although they are expensive. Even expensive seeds are cheaper than plugs though. What concerns me is its thirst. I'd probably have to commit to watering it whenever the soil dries out. Maybe I could make some kind of basic drip irrigation system for it. Also the seeds need a long cold period to germinate. So it wouldn't help me this season. I do intend to sow some in the fall. I just love that plant.

In terms of versatility, aggressiveness, attractiveness, and height Creeping Jenny seems hard to beat. One problem is the lack of seed. That makes it expensive to establish in any reasonable amount of time. I just ordered around 30 plugs of the 'aureus/goldilocks' chartreuse cultivar. As soon as the plugs grow out I'm hoping to help them to spread even further by clipping and rooting some cuttings. Nevertheless I am not expecting them to spread fast enough to stop the weeds this season. Or even the next. And, since I know next to nothing about gardening or botany, that's where things get complicated.

I'm having trouble coming up with a strategy. My goal is to establish a weed-choking, attractive ground cover ASAP. Creeping Jenny would be my first choice, but I'm not sure I am willing to wait 2-3 more seasons for the Lysimachia to form a dense, weed-choking carpet. I'm trying to figure out if there is some way to plant something that will fill in the gaps left after the Lysimachia plantings.

Presumably I should be thinking in terms of an annual or just something less hardy than zone 6. Maybe 8+ to be safe. And something that doesn't spread or spreads very little and can grow from quickly germinating seed. I guess my first question would be whether this idea of a temporary filler plant to help battle the weeds makes any sense. I don't know exactly how fast the Lysimachia will creep. I certainly wouldn't want to obstruct its path with a competing plant. Unless the filler plant is a very fast grower, it might not even out-compete the weeds anyway. It may even make weeding more difficult by mixing with the weeds so that I cannot spray glyphosate without also hitting the filler plant foliage.

On the other hand I really want to get some ground cover down there. Despite my desire for a Creeping Jenny monoculture in the front yard, it is difficult to resist throwing something in the gaps. But the filler plant idea is starting to seem like more and more of a bad one. Perhaps it would be better to put some of the money I'd save by not buying any more plants toward a pre-emergent herbicide. Since I'm not propogating the Lysimachia by seed, presumably a pre-emergent wouldn't hurt. It would just have to no longer be active in the fall when I sow the Rush seeds for the spring.

That's another complication. Where to place the Rush seeds. Maybe I should divide the yard in half and plant the Lysimachia on the drier top of the hill and plan for a Rush emergence at the wetter bottom half of the hill next spring. That strategy would seem to invite a temporary non-hardy annual ground cover at the bottom of the hill where it wouldn't be in the way. Any suggestions for that? The idea of Corsican Mint has occurred to me. Seems like a nearly ideal ground cover aside from its delicate and fussy nature. The seeds are kind of pricey, but it's something I'd love to work with. Like most mints, "well-drained" soil seems to be a requirement though.


Follow-Up Postings:

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RE: low ground cover on poorly drained clay

Did your weed control person say which weeds are regarded as pest plants for your area? And why?

If you want any sort of success with your yard - you will HAVE to put back the soil you've been scraping off. That's where the food and water are for the plants and soil life.

Gardening on clay: there is a 'best time' for cultivation. It's like Goldilocks' porridge. Not too wet. Not too dry. You could either use a heavy-duty spading fork - or a mattock, or a big, long-handled shovel with an oval tip. The last two are good for putting in shallow drains, too.

Does your local civic administration allow you to cover your yard with mulch? You'll still get weeds. No doubting. Birds and wind - and even the rain, will bring in seed. The mulch makes for easy weeding, though.

At the moment, because you've scraped off the top/humus layer, all that will grow are pioneer species - mosses, liverworts, annuals or tough shrubs/trees. And they'll be small for a long time, until the food levels rise. Maybe five years and more.

I like your idea of the rushes. Are you obliged to have a monoculture? Or could you create an ephemeral wetland? I think they're called 'rain gardens'
This link might help: www.aucklandcouncil.govt.nz/.../raingardenconstructionguide.pdf. There are plenty of others on Google, though.

The main hesitation I would have lies around using shingle or pebbles as a mulch. Weeds and busy annuals love it! Seed madly in it! Takes way too much time to keep looking tidy...

First step, for me, would be to return the soil you've removed as evenly as possible.

If it's not a huge area you could solarize it to kill emerging weeds (clear plastic plus enough damp to get them to germinate, and let the sunlight sizzle them). Or lightly and regularly (weekly) cultivate to disturb the emerging seedlings, adding a thin layer of bought compost - no more than half an inch deep and ruffle it through the top soil. Do that compost adding two to four times over the rest of the summer, and water once a week or so.

If wind is a problem in your yard - you'll have to mulch to protect your soil. Stop it from flying away when it's dry. Can you get mulched leaves from your tree feller fellas either free or cheaply? Lay them on so the ground is covered and there's about two inches thickness. Not too much. You want it to rot away over summer.

Stay away from the glyphosate. You want (well, maybe not, yet you NEED) your soil life to restart, and poisoning is not going to help.

I didn't pick up whether your yard is very sunny, or quite shaded. If it's shaded, the Creeping Jenny should be fine though the rushes might protest and show their displeasure by dying.

While you're waiting for the soil to restart into health - you could also be bulking up your chosen ground cover. Little offsets in pots ready to make plugs of your own. Check out Freecycle or similar for a source of small pots.

When you've got your cover going again - annually add that thin layer of compost in and around the plants and on any bald patches. So long as you don't smother them or their growing points they'll be fine. It will build your soil, help hold the moisture for longer over summer, make removing weeds easy, and feed your groundcover, as well as help it to spread.

Good luck.


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