Where I am we get a lot of rain for about half of the year. Well…we are supposed to get a lot of rain for the second half of the year….but climate change. While we don’t have the resources yet, my goal would be to be able to only water my garden with rainwater. My thoughts on this really started with this simple logic, “If chlorine was meant to kill bacteria in the water that we drink then isn’t it also killing some of the good bacteria in my soil?” After going down the internet rabbit hole of information and trying watering exclusively with rainwater on my plants I was convinced. Rainwater is better for plants than tap water.
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What Happens When You Water with Tap Water
Most tap waters are too alkaline (usually between a pH of 7.5 and 8) and can make it harder for your plants to take up nutrients. Under the soil’s surface, your plant roots are under constant “negotiations” with the soil around it to give up some of its nutrients. When the soil is too alkaline your plants are at a disadvantage and may not be able to access the nutrients, even though they are present in the soil.
While the effect of chlorine on killing bacteria is reasonable for potable water in our homes it wreaks havoc on the soil microbial population. Also, most tap water doesn’t contain just chlorine. Tap water also contains fluoride and minerals such as magnesium and calcium. The chlorine and fluoride in tap water can damage plant cells causing necrosis (which shows up as the browning of leaf tips). Nearly all plants are susceptible to chlorine toxicity if the levels of chlorine in the water are high enough. Prolonged watering from water with high levels of chloride can stop plants from taking up available nitrates. If you notice your plants just aren’t as green as they should be making the switch from tap water to rainwater might be an easy fix.
If your tap water contains high enough levels of sodium this can also damage the soil structure. Good quality garden soil will clump together forming aggregates that help hold nutrients in the soil. Sodium will have a negative effect as it fragments these aggregates and results in visible cracks on the soil surface.
Why Rainwater is Better for Plants
In contrast to tap water, rainwater is usually slightly acid (normally rainwater has a pH between 5 and 5.5). As the rainwater travels from the sky to the surface of the earth the CO2 present in the atmosphere makes it more acidic. The Lower pH makes more nutrients available, plants take up more nitrogen and their leaves look greener. Therefore, a slightly acidic water pH will make nutrients more available for plants and better for overall soil health.
Nitrogen in Rainwater
Rainwater, particularly rainwater during a storm can be extremely beneficial to your garden. Lightning can add nitrogen to rainwater. Nitrogen makes up 70% of the atmosphere. The heat and pressure lightning generates provides enough energy to break down and convert atmospheric nitrogen into several reactive nitrogen compounds. When mixed with oxygen and water in the atmosphere the resulting rainfall will contain greater levels of nitrates and ammonium. Once the raindrops reach the ground they deposit ammonium and nitrates that can be used by the plants and/or soil microorganisms. If you’ve ever noticed your plants looked greener and happier after a storm, it wasn’t your imagination.
Rainwater doesn’t just add nitrogen to the soil, it also makes other micronutrients more available as well. The lower pH helps to release micronutrients such as zinc, manganese, copper and iron that are essential to plant growth.
If plants are overwatered or there is sufficient rain plants can become waterlogged. This can lead to anaerobic soil conditions which then leads to root rot. However, Rainwater tends to have a higher level of oxygen and is less likely to suffocate plant roots. If you are a houseplant person, this is one of the reasons why it is much easier to overwater your houseplants than it is for your outdoor plants to become waterlogged and die off after heavy rainfall.
Benefits of Rainwater for Plants
Rainwater is very beneficial when it comes to improving some aspects of your garden. I compare it to nature putting things back the way they should be. It does this in a few ways.
- Rainwater leaches salts down beyond the root zone. These salts (e.g. sodium which we described earlier) can inhibit plant growth if left to build up in your soil. The effects are most prominent after winter in temperate climates, or after several days of rain in the Caribbean. The effects are enough for an observant gardener to notice significant plant growth in a relatively short period of time.
- Rainwater is like a shower for plants. It washes off any mineral deposits, dust and pollutants that may cover the leaves. This makes more sunlight available to the leaves and makes photosynthesis more efficient.
The simplest way to harvest rainwater is to collect it from the guttering of your roof. You can make one yourself with some simple tools and a rain diverter kit for easy setup.
Quick Tips on Rainwater Harvesting
- Don’t let cost get in the way. Do what you can with whatever you have and improve as you go. Don’t let the goal of perfection stop you from starting.
- Keep the container covered to avoid mosquitos. Mosquitoes can be vectors for disease such as dengue and yellow fever. To avoid creating a breeding ground close to your home, be sure to keep your containers covered at all times.
- Collecting something is better than collecting nothing. 1 inch rain will collect 600 gallons from a 1000 square foot roof. While you may not be able to store all the rain water your garden would need. For most people, it is indeed possible. And, as you continue along your gardening journey you will be able to better estimate what your specific water requirements are.
- Use a dark container. This will reduce the amount of algae growing in your container this can clog up your filtration system
- Make sure your container is food safe. If you are using plastic barrels or tanks to store your water they should be plastic recycle numbers 1, 2, 4, and 5
- You may lose some nitrates but that’s ok. Some of the nitrates might be lost as it is stores but it will still be beneficial because of its softness, pH and lack of chlorine and fluorine.
Rainwater has significant benefits for your plants. By using rainwater you can avoid problems such as fluoride toxicity (that can cause problems such as burnt, discoloured or spotted leaves) or chlorine toxicity (which is usually manifests as burns along the edges of the plant leaves). While we may not be able to harvest enough water for our garden year-round it is still worth starting. The more rainwater we use the better it will be for our soil, our plants, and ultimately our families.
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