What Are Some Problems With Rain Gardens? {Are They Safe?}

Are you wondering if a rain garden is right for your lawn? Could rain gardens cause more harm than good? In this article, we’ll discuss some problems with rain gardens and if they are worth it.

What Are Some Problems With Rain Gardens? Rain gardens can create issues with drainage and the accumulation of pollutants and bacteria in the basin are causes for concern. Flooding and erosion could also result from rain gardens that are poorly created. 

Why Are Rain Gardens Bad?

There is a debate going on whether or not rain gardens are actually worth having on our lawns. The soil in rain gardens including the mulch within can contain trace particles, pollutants and hold metals such as:

  • Copper
  • Cadmium
  • Lead 
  • Zinc

The concern is that these metals can get absorbed by the plants and the vegetation in the rain garden. The issue is how much? We need to dig deeper to see if the impact of these metals go beyond low levels and become a detriment to your garden.

  • Flooding
  • Pollution
  • Erosion

It’s rare for rain gardens to cause this much damage, but it happens when they are poorly designed. No one wants excess pollution, floods or erosion to occur to our rain gardens.

Does Pollution Soak Into Rain Gardens?

The pollution around the rain garden could come from roofs and water run-offs in the neighborhood or through chemicals in the lawn. Will they get soaked into the rain garden? Yes. Will they remain there? Not if the rain garden is properly designed.

Storm water contains dirt, oil grease, phosphorus and lead. All of these are very concerning, but we have to look deeper. The concentrations of these pollutants are actually very small. Trace amounts shouldn’t be a grave concern.

We’re all worried about pollution, but your rain garden isn’t turning into a toxic waste site. It only holds in small amounts of these pollutants that shouldn’t be a detriment to your rain garden and surrounding lawn.

What Happens To The Pollution In Rain Gardens?

What’s great about rain gardens is that they catch oil, grease and metal pollutants to keep them out of streams and lakes. Wildlife and contaminated water do not mix. Fishing and polluted lakes also do not sound nice at all.

Rain gardens do their part to decrease pollution seepage into larger bodies of water. Rain gardens are also referred to as bio-retention systems as they capture bacteria as well.

If Rain Garden Is Helping the Environment, What Is It Doing To My Lawn?

The rain garden is working overtime. Here is how your rain garden is getting rid of pollutants to not harm your lawn.

  • Volatilization
  • Sedimentation
  • Adsorption
  • Microbial action
  • Plant resistance and uptake
  • Filtration


This is when the pollutants in your rain garden like grease or petroleum evaporate. Instead of running off into lakes or streams, the evaporation is only possible because the rain garden has been able to capture them.


The heaviest particles seep into the soil. It’s important to discover just how much of these heavy particles are contained in the soil. Scientists continue to study this, but the news so far is positive. The amount of particles in the soil are miniscule and should not be a cause for concern.


The storm water sinks into the soil and gets absorbed. It’s mixed with water and microbes. It dissipates as well in order to not contaminate the soil.

Microbial Action

The pollutants in the soil can also be broken down by bacteria and microorganisms within the soil. They make the particles less harmful to the environment.

Plant Resistance And Uptake

Plants also eat up pollution. They can suck in the pollutants through their roots and get rid of it in small amounts. Most of time these are decaying plant materials that we don’t see at the surface of the rain gardens.


If there is a filter in your rain garden, then it’s going to capture these particles as well. A great rain garden has some filtration installed to assist in cleaning up the surrounding environment. This is recommended and creates a well designed rain garden.

Are Rain Gardens Contaminated?

Rain gardens capture water and run-off from roofs, streets and petroleum hydrocarbons from vehicles. Scientists continue to research this and current findings suggest that although rains gardens are getting contaminated, the amounts are far less than dangerous.

There regulatory actions levels that are deemed safe or dangerous. The levels found in rain water were about a thousand times safer than regulatory levels would deem dangerous. The amount of pollutants, although present, are insignificant.

The pollution got absorbed by plants, soil, microbes, evaporated, dissipated and destroyed. Research also suggest that petroleum pollutants get eaten up by microbes in as little as one week.

Do Rain Gardens Have Standing water?

The water doesn’t stand in rain gardens . Do not be concerned about mosquitoes reproducing in rain gardens. The design of the basin is not deep enough for the water to stand. It will dry before mosquitos have a chance to reproduce.

Many days of rainfall could create some standing water, build it will soon soak in. Rain gardens are shallow and built on soil with enough drainage to prevent any pests from using it as a breeding ground.

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Are Heavy Metals Stuck In Rain Gardens?

These metals including, copper, zinc and lead are present in rain gardens, but their volume is tiny. A study in 2003 indicated that it would take two decades before the amount of heavy metals in a rain garden even reached EPA limits in the United States.

Compare that to the amount of heavy metals in compost and the amounts are far less. The metal contamination in rain gardens fall way below safety standards. The heavy metals are not enough to make you think twice about serving the environment with a rain garden.

Do Unhealthy Bacteria Build Up In Rain Gardens?

There are countless microorganisms in rain gardens through storm water. These include:

  • zooplankton
  • protozoa
  • nanoflagellates
  • microflagellates
  • amoeba

In most cases the sunlight kills the microorganisms. There is research suggesting that the bacteria leaves the water in rain gardens to contain higher levels than before entering into it. Does the bacteria gets worse?

Experts are starting to conclude that animal waste from birds, pets or wildlife further re-contaminates the soil in the rain garden to leave it with more bacteria than before the storm water came in.

The bacteria rises, but it doesn’t contain harmful human waste or pathogens like viruses. It contains mostly animal waste like bird poop. Sure, this bacteria can be proven to be present in rain gardens, but they are not likely to be of risk to humans.

The low risk of harmful bacteria build-up is inconsequential and cannot convince us to remove our rain gardens.

Do Viruses Live In Rain Gardens?

Viruses that can cause diseases have been found in rain gardens, but the levels were extremely low. It’s easy to aggregate this fact and leave readers fearful, but the amounts are too low for fear mongering. The contamination is well below the soil in trace amounts and humans are protected this way.

Sunlight, healthy bacteria consumption and run-off destroys almost all of these pathogens and viruses. Further research has been conducted and many of these pathogens are animals related and known to not affect humans.


Rain gardens are safe. It is still advised to wash your hands well with soap after handling the plants and vegetation in rain gardens. The heavy metals are minuscule and absorbed by microbes and plants or destroyed by sunlight and run-off.

Rain gardens are attractive and can increase property value. They serve a purpose to prevent pollutants from seeping into our lakes and streams. The wildlife, fish and environment thank us for keeping our rain gardens.

The erosion or flooding risks from rain gardens are rare and only present when they are poorly designed. This article is not a how-to for rain gardens and we encourage you to research further if you wish to set one up.

We hope for those who have rain gardens, to keep them based on research that shows the harms are not a threat to humans. They fall thousands of times below safety standards and the benefits far outweigh them.

Frequently Asked Questions:

Are Rain Gardens High Maintenance?

Rain gardens don’t need as much care and chemicals that your lawn does. They capture the run-off from roofs, driveways and storm water. Rain gardens work on their own to allow this run-off to seep into the ground at a slow and steady place. One set up, they are not high maintenance.

How Do Rain Gardens Work?

Rain gardens take in water from rooftops, driveways, patios and storm water. The garden itself acts as a basin to capture the water and holds it in. The water slowly seeps into the soil. The plants and microbes in the soil along with sunlight help get rid of the pollutants.

How Is A Rain Garden Built?

Rain gardens are built by finding a flat strip of land beside a road, driveway or lawn. Swales are channels that are built to create run-off into the rain garden. The storm water from gutters or driveways can flow into the space designed for the rain garden to absorb the water. The soil, plant roots, microbes and sunlight help to keep harmful levels or pollutants and pathogens very low and safe.

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