Perhaps the greatest challenge I have as a New York City garden designer is managing water. Typically this is in the form of remediating existing drainage problems.
Soil materials are compacted, loosened and amended over time, most often during construction. Grades are changed, plant cover removed and altered. Building run-off and surrounding conditions all contribute to this situation. In a suburban environment the challenges may be more obvious as land is spread out. In an urban environment, a city garden design situation can be more complex.
Water doesn't drain effectively
An obvious and revealing method to understand your problem is to pay attention to what happens after a heavy or concentrated rainstorm. Early Spring, usually offers heavy precipitation.. remember "April showers bring May flowers?". Take pictures and compare from several rain showers. You know you have a drainage problem in your garden when heavy or even moderate rain leave puddles that take forever to drain. Or you may find out, to your dismay that under a few inches of okay soil in your yard is a stubborn layer of packed clay.
In really damp areas (especially in humid periods or in shady spots) water, whether from rain or from your sprinkler, can be slow to evaporate. This leaves plant vulnerable to diseases, particularly on foliage. The solution is to improve the air circulation, by pruning overhanging growth and supplying water to the roots instead of allowing it to splash the entire plant.
Poor drainage is a challenge for garden plants that are not adapted to wet or commonly flooded sites. More importantly, poor drainage may cause building problems. Here are solutions to remediate for drainage in a garden:
1. Try improving the soil: Dig in lots of organic matter. (COMPOST!) Soil with high organic-matter content allows excess moisture to drain through while absorbing needed water. Compost is the cure-all to so many problems in a garden.
2. Build and garden in raised beds: You control the soil within, and thus it drains well and your plants are happy. Problem averted.
3. Permeable surfaces: My tried and true solution as a garden designer is to build with permeable surfaces and aggregates. Put pavers on soft beds, use gravel for paths.
Pervious surface photo: Todd Haiman Landscape Design
Pervious surface photo: Todd Haiman Landscape Design
Gravel path photo: Todd Haiman Landscape Design
4. Create a rain garden or a bog garden, and plant water-loving plants: Choosing plants depend upon your locale, hardiness zones and amount of sun. In a New York City garden design I would recommend asters, beebalm, coneflower, tickseed, ferns, rushes, dogwood shrubs, etc. Once established, the deep roots of native plants increase the water holding capacity of the soil and minimize potential for erosion. At the bottom of this page is a link to a thorough listing of native plants for a rain garden.
Rain garden plantings illustration: Steve Buchanan
Rain garden plantings photos: Vermont Wildflower Farm
5. Route water flow away from the garden area: Just get out there with a trowel or shovel and create some diversion channels. Of course, you don't want to send the problem to another important part of the yard or foist unwanted, excess water on your neighbor. Send it down the driveway and on into the street, or into the gutter if your local ordinances allow this water needs to head for the storm drains. (This is not achievable in a NYC garden design, as local laws want you to manage stormwater onsite and not divert it. Therefore, if this plan isn't practical, dig a hole nearby, fill it with gravel, and route the channel there.)Fertilizer runoff can harm rivers and streams, so if you use this technique, be especially careful that you don't use excessive fertilizer and that you apply it at recommended times so the plants use the nutrients rapidly.
6. Make a gravel channel: Follow the advice about rerouting water flow, but dig the channel somewhat deeper and fill it with crushed gravel or pebbles. You can hide it from view for some or all of its length by scooping a little soil over it. It'll still do its job of slowly but surely taking the water away. A more aesthetic garden design solution for larger properties is to create a dry river bed.
Dry river bed photo:ThisOldHouse
7. Use perforated plastic pipes, lightly or deeply buried, to divert the water to where you want it to go: Home supply stores sell pipes specifically for this purpose. These pipes usually come in various forms and sizes of plastic; clay tiling is also available, but it's too heavy and expensive for most homeowners.
If the problem is severe and you can't seem to solve it, drainage tiles, a French drain, or a curtain drain are options: Installing one of these systems can be an expensive and involved process. Hire someone experienced to advise you, explain the options, and install.
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**This post is "inspired" by a 2014 job with one of my favorite clients. We patiently worked together through a good deal of challenges to manage stormwater runoff and flooding issues on their Park Slope, Brooklyn garden.
