Trees/plants to mitigate standing water in yard after heavy rain
September 15, 2020 6:51 AM   Subscribe

My area had record-breaking rain last week, with the result that water pooled in various spots around our yard - notably the garage, which ended up with 4 inches or so of water in it. Can we do anything with plantings such as trees or shrubs to reduce this impact in the future?

This image shows a photo of our street (in Maryland, US). Unlike nearby streets which had fast flowing runoff from overflowing storm drains, this was rain water that accumulated and could not drain away fast enough. It did all subside within 24 hrs. Given that heavy rain seems likely to occur more often in future, could landscaping with trees or shrubs help reduce this effect? There is one area we have earmarked for a rain garden and we have lots of other space where we could plant more (native) shrubs and smallish trees. The yard is mostly grass now, and we definitely want to change that. Is there anything else we could look at? Not intending to do major earth-moving or reconstruction of the garage, and am not expecting huge changes with plantings. (The cinder block garage was pretty prepared for this already, with most things up on bricks or pallets.)
posted by sizeable beetle to Home & Garden (13 answers total) 2 users marked this as a favorite
The biggest part of it is making sure that the ground is not compacted, but permeable. Turf is bad at that.

Appropriate grading will help and any low spots will be good locations for rain gardens. Remember, plants in rain gardens should be feast-or-famine plants, adapted to both dry and flooded conditions, unless your rain garden is permanently wet because of consistent rains and poor permeability.

Trees and shrubs can help too but mostly because their root systems break up the ground so it drains rather than turns into a sheet pan. If you are in drought conditions (like we are up here in much of the north east) there's not much that will help because the ground is dry like concrete and will actively repel the water when it storms.
posted by lydhre at 7:02 AM on September 15 [2 favorites]

Appropriate grading for the win.
posted by cooker girl at 7:06 AM on September 15 [4 favorites]

I lived in Rockville, Maryland, and my recollection is that most of the soil around the are is clay. I would normally recommend adding drainage to the area, but even if your yard drains, the rest of the neighborhood doesn't look like it allows your rain to go anywhere. So even if you mitigate your rain, where will it go? The overwhelmed sewer system?
posted by Hey, Zeus! at 7:06 AM on September 15 [1 favorite]

Look into building a rain garden, which isn't so much about plant life and moreso about a depression to collect rain runoff with plant life tolerant to wet conditions.
posted by Dmenet at 7:21 AM on September 15 [1 favorite]

Hey, Zeus! I believe that our soil type is fairly well-draining sandy loam. You are correct that if we simply divert surface water to the street, it would just end up in the flooded stream system nearby.
posted by sizeable beetle at 8:01 AM on September 15

Eucalyptus have been used all over the world for draining swamps... no idea if they'll grow in your zone tho.
posted by fingersandtoes at 8:44 AM on September 15

Swale or bioswale are also good search terms
posted by momus_window at 8:56 AM on September 15

Grading just makes the water someone else's problem. Plants can't absorb it fast enough. You need to change the soil structure to make it more permeable and absorbent. The most effective, low effort way to do this is to add organics by sheet mulching (putting down cardboard, and then a thick -6+ inches- layer of wood mulch. You can also add deep rooted perennials, especially the next year after most of the weeks have been killed off under the cardboard.

Adding organics makes sore topsoil more sponge-like in the first place, but it also brings in worms and other critters who dig around and move the soil and break it up, make it more able to absorb water. The deep rooted perennials do similar things, creating channels deep in the soil for water to run down into.
posted by rockindata at 9:55 AM on September 15 [2 favorites]

Any examples of deep rooted perennials? Does that mean plants with taproots?
posted by sizeable beetle at 10:46 AM on September 15

Does that mean plants with taproots?

No. Some plants with tap roots are fairly shallow, and many deep rooted plants don't do a primary tap root. See some examples and illustration here.
posted by SaltySalticid at 11:12 AM on September 15

In my opinion the best thing to do would be to dig 12 inch deep trenches and install permeable underground piping into the soil. If you are going to build a rain garden or a swale anyways, you will be doing some digging.

10 ft long 4" perforated pipe

A catch basin at each end

A 1inch-ish layer of the cheapest pebbles you can buy under the pipe (for additional drainage)
wrap the permeable pipe in drain sleeve to prevent roots from clogging it

The digging is the only part that sucks, the rest is super easy and will take all that water, put it underground where you plants need it, and your rain garden and the grass over the pipe will be super green. If you get the catch basins with 2 pipe ends instead of 1, you can just buy 1 section of pipe (total cost about $40 for everything) and put 10 feet of pipe underground and see if you are happy with it, and add on more later.

If you have some spare money, you can rent a machine that does the digging for you. Makes it even easier. I think each section of pipe holds about 6 gallons of water, but rain will be watering the top of the soil and these will be watering deep. I have about 30 feet installed; the only time my yard has any standing water is when a hurricane-remnant storm rolls through and it rains like 15 inches in a 2-3 days.

Grass (due to the huge surface area it covers) is actually one of the fastest drinking most water intensive plants there is - so I honestly don't think any other plant would drink more standing water without planting at a similar density.
posted by The_Vegetables at 12:45 PM on September 15

Our previous house (new construction) had a poor draining backyard. I called the county, and they sent somebody over to look, and he said I could spend a few grand on a French drain system or I could plant a couple of weeping willows and red maples and let nature work. I opted for the trees, and they thrived, and significantly dried the yard over time. This was in NOVA. Just be careful about planting too close to the house as the trees roots will tear up pipes.
posted by COD at 2:31 PM on September 15

Wrapping willows will definitely dry up wet spots, not sure how feasible those are for you, they can get big.
posted by theRussian at 5:12 AM on September 16

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