How Is Over Irrigation Damaging To Soil

As plant parents, we’re usually preoccupied with making sure our plants are getting enough water. Not so many gardeners realize, however, how is over-irrigation damaging to the soil. Probably because it’s counter-intuitive. Over-watering produces the same signs as under-watering.

I know my alarm bells go off when I see a plant in my garden that is starting to wilt or dry out. On instinct, my first reaction is to overcompensate and give lots of water. Over-irrigating decreases aeration, encourages compaction, and shifts the chemical balance in the soil. Damage to the soil from over-irrigation will also impact plant growth.

It is quite easy to over-irrigate your garden, especially for excited new gardeners. Luckily, over-watering is usually easily preventable. Knowing how over-irrigation damages the soil will help you fight the tendency to over-water. Keep reading to learn why over-watering is bad and how to prevent it. 

What is irrigation

Irrigation is the technical term for water applied to grow crops. Irrigation systems, for example, refer to how growers keep their crops watered.

In gardening, there are many different types of irrigation systems. From complex drip irrigation systems to simple sprinklers, hoses, and even hand watering with a can.

Naturally-occurring rainfall is also a form of irrigation. There is no best irrigation system, so choose whatever works for you, your space, and your plants.

Like with all things plant care, you need to provide balanced irrigation. Too little water and your plants will wilt and die. However, too much water will damage your soil and stunt plant growth. Keep reading to learn how over-irrigation damages your soil.

How is over-irrigation damaging to soil

The primary reason why over-irrigation is damaging to the soil is that it affects aeration, making conditions anaerobic. Lack of oxygen isn’t the only way over-irrigation affects drainage. Waterlogged soils are also particularly sensitive to compaction.

Overwatering also has secondary effects on plant growth, caused by damages to the soil. Stunted plant growth is caused by compromised roots, increased salinity, nutrient leaching, and rot. If allowed to persist over-irrigation can lead to dense, swampy soils where common garden crops won’t grow.

Aeration

Over irrigation primarily damages the soil by reducing the amount of oxygen in the soil. As water infiltrates the soil, it fills the pores between soil particles. These spaces are normally used for oxygen to circulate so aeration is compromised.

Plant roots and their beneficial bacteria need oxygen to live. Without oxygen, the plant roots will start to rot away. So prolonged wet soils will deprive plant roots and microorganisms of essential oxygen.

If the waterlogging is short-lived, plants will survive the flooding and bounce back. More than a few days will cause your plants to stop growing and eventually rot away. If your plants are in a period of rapid growth or setting fruit, waterlogging during this period will greatly affect your yields.

water irrigating crops in a field
Water is essential to plant growth, but over-watering can be just as harmful.

Another consequence of low oxygen levels in the soil is the accumulation of carbon dioxide and ethylene. As well as an increase in disease bacteria. Greenhouse gases trapped in the soil will further stunt plant growth. While weak plants will be much more sensitive to increased disease pressure.

Reverse the effects of waterlogging by promoting healthy soil life. The microbes living in your soil naturally aerate the top layers and will restore balance for you.

Soil Structure and Compaction

When soils are wet, they are more susceptible to compaction. Compaction happens when the space between soil particles becomes smaller. Waterlogging causes compaction through the dispersion of clay soil particles.

Compaction will become more severe if the pressure is on wet soil. Walking, driving, or putting pressure on waterlogged soils will easily compact the ground. Compaction is damaging to soil structure, affects plant growth, and is extremely difficult to correct.

Avoid one of the biggest consequences of waterlogging by not treading or working waterlogged soils. Wait for the ground to drain naturally and then start amending the soil or building raised beds.

Nutrient Leaching

When too much water is applied to soil the vital nutrients will be washed away. As excess water drains (usually on the surface), essential nutrients like nitrogen, potassium, and phosphorus are lost.

On one hand, this means that plants won’t have ‘food’ to grow, but it can also be dangerous for water pollution. Chemical fertilizers, for example, can be seriously dangerous for fresh water and groundwater when over-watering causes nutrient leeching.

Combine nutrient leaching with compromised roots due to lack of oxygen, and your plants will be in trouble. The weak roots won’t be able to uptake the limited amount of nitrogen, for example, and will stop growing. Decreased nutrient uptake affects general plant growth and will reduce yields if waterlogging occurs while the fruit is setting.

Salinity

Overwatering causes nutrients to drain away from the soil. This increases salinity. Fewer nutrients, more salt, and a compromised root system (caused by lack of oxygen) will affect plant growth. 

Water has mineral salts that accumulate in the upper layers of soil as the humidity evaporates. Soil that becomes waterlogged has more sulfates deposited in the soil. An accumulation of salts makes the soil around the root zone inhospitable for garden plants.

Over irrigation vs deep watering

Over irrigation to the point of waterlogging is damaging to the soil, while deep watering promotes strong plant growth.  Plant care revolves around finding a good balance. Lots of sun, but not too much. Plenty of nutrients, but without overdoing it. Lots of water, but without over-watering.

Waterlogging is when the soil stays consistently wet and can’t dry out. When I talk about damage to the soil caused by over-watering, I’m not talking about the heavy rain that came down last week. I’m referring to damage caused to soils that sits saturated with water for days or weeks on end with no break.

water irrigation hose reel applying water to crops in a field
Water being applied large-scale by a rain gun moved through a field by a powered hose reel.

The difference between over-irrigation and deep watering has to do with the frequency. Deep watering once or twice a week is recommended compared to shallow watering every day. Providing deep watering allows the moisture to reach further down in the soil, causing the plant’s roots to grow deeper. Deep roots make for more resilient plants.

Now that you know the difference between deep watering and over-irrigation caused waterlogging, you can make your irrigation plan.

How to prevent over-irrigation

Over irrigation is fixed by watering less often. In most soils (expect sandy soils), daily watering doesn’t allow the soil to ever properly dry out. Unrelenting watering will lead to waterlogging. 

When friends ask me why their plants aren’t growing well, I ask how often they water. Enthusiastic plant parents with the best intentions often reply proudly that they water every day. Just like that, we find the root cause for why their garden isn’t doing well.

You can prevent over-irrigation from damaging your soil by watering less, amending with compost to increase drainage, or planting in raised beds.

Check soil moisture manually by digging in 3-4 inches with your hand and checking the soil is damp. it should be damp but not sogging wet. Alternatively, get a soil moisture meter to help you make the decision.

If you are manually watering your plants, over-irrigation is easily fixed. Just don’t water so often. I give most of my plants a deep soak twice a week, which is plenty until the hottest summer months.

If rainwater is causing excess moisture, then you’ll need to amend the soil or build raised beds. If you think amending the soil will be enough, incorporate three parts compost and one part sand to help drainage. This means that when it rains the soil will have an easier time absorbing and distributing the water.

In extreme circumstances where amending with compost isn’t enough, you might need to grow your plants in raised beds. Planting in raised beds helps with drainage. The excess water can drain away below. 

Alternatively, you can embrace the humidity. There are lots of plants that have evolved to love extremely wet conditions. These water-loving plants will do great in your over-watered garden. Use the space to grow an Elder tree, peace lilies, or irises.

Summary

While everyone knows that under-watering can hurt your plants, it’s less common knowledge that over-irrigation is damaging to the soil. Waterlogged soils reduce aeration, increases salinity, and can surpass crop field capacity. All these consequences will impact plant growth by promoting diseases like rot or stunting growth.

Lots of watering means a higher water bill, more work for you, damaged soil, and stunted plant growth. Instead, try and establish a watering strategy where you are soaking the soil deeply twice a week. To prevent problems from waterlogging there are a few things you can do. Create an irrigation plan to water deeply a couple of times a week, amend your soil so it drains more easily, or choose plants that are naturally happy growing in wet soils.