In dry climates, every drop of rainwater is incredibly valuable. It’s crucial to make the most of it by collecting and using it in your garden. Rainwater is ideal for plants because it has had a chance to warm up and is more beneficial than tap water. During a dry spring, having rainwater on hand becomes essential for keeping your garden thriving.
Rainwater from a rain barrel is far superior to tap or well water, which is often cold and may contain chlorine. Rainwater is typically at a more suitable temperature for plants. Investing in a good rainwater harvesting system is worthwhile—not only does it save on water costs, but it also provides better quality water for your garden.
The Rainwater
Rainwater is a free and relatively clean resource that falls from the sky. However, harvesting it may not be legal in all areas. Generally, using rainwater solely for garden purposes is not an issue, but it’s always best to check with your local municipality if you’re unsure.
As a rule of thumb, 1/2 inch of rainfall yields about 0.3 gallons per square foot of roof area. So, a 1,000-square-foot roof can collect around 300 gallons of water—quite a substantial amount.
The quality of rainwater depends on your roof’s material. For garden use, the main concerns are wood shingles treated with fire retardants and copper roofing, as these can introduce substances that may be harmful to plants.
The Rain-Collecting Receptacle
To collect rainwater for gardening, you’ll need a suitable and durable receptacle. Options include barrels, totes, containers, ponds, or tanks. The size of the container should match the size of your roof. Here are some choices to consider:
You can start with any container to catch rainwater, but 45-gallon barrels are a popular choice. Despite their size, these barrels are quite durable and come in various colors and materials. For a 45-gallon barrel, ensure you have a good overflow system to manage the water from your roof.
IBC totes are another common option for rainwater collection. They typically hold around 275 gallons (about 1,041 liters). However, they aren’t the most durable, so be prepared to replace them every few years.
For a larger setup, a 20′ x 30′ garage roof can collect approximately 360 gallons (about 1,363 liters) from just 1 inch of rain. The water from the top tote is channeled through a plastic tube to the top inlet of the bottom tank. With a pond liner covering the garage roof, the water quality is generally very good. For more durability, consider ground storage options such as tanks or ponds.
The Overflow
Rain receptacles have a maximum capacity, and when they reach it, excess water needs to be handled properly. An effective overflow system is essential. A drain hose is a practical solution for managing overflow. During heavy rainfall, a significant amount of water can flow through the overflow, so ensure it’s well-positioned.
Place the overflow outlet away from your building’s foundations. Additionally, you can repurpose the overflow water to nourish perennial shrubs and trees, or even create a self-watering system for your garden, such as the one we designed for our raspberry patch.
Dirt, Algae, And Bugs
Rain barrels can attract more than just rain; they often gather dust, dirt, and insects. If you’re using a simple barrel, keep the lid securely in place but cut a hole just large enough for the downspout. This helps prevent debris and mosquito breeding. For barrels without lids or open barrels, consider installing netting to keep out pests.
Attach a paint strainer to the downspout extension hose to filter out roof debris. These strainers are inexpensive and can be easily cleaned or replaced each spring.
Algae tends to grow in bright, moist environments, but it takes time to develop. A dark-colored barrel will inhibit algae growth more effectively than a transparent one. You can also paint or wrap the barrel to block light. Positioning the barrels on the north side of your house, where sunlight is less intense, can further help reduce algae growth compared to the sun-drenched south side.
Preparing the Rain Barrels for Winter
As temperatures drop, water inside rain barrels can freeze and expand, potentially damaging the barrel. To avoid this, it’s crucial to empty your water harvesting barrels before winter sets in, especially in colder climates. During fall, trees, shrubs, and perennials still need watering to help them survive the harsh winter. This coincides conveniently with the need to empty your rain barrels, making it part of your overall garden winter preparation.
Simply emptying the barrels isn’t enough, though. If you don’t properly divert the downspout discharge, melting snow during a warm spell can lead to water collecting back in the barrel. Even if the barrel was emptied in the fall, water can still enter if it’s not disconnected from the rain gutter. This can result in the barrel freezing and bursting from heavy frost.
To keep a greenhouse from freezing during the winter, especially in colder northern regions, good insulation, ample thermal mass, and a backup heating system are essential for growing winter vegetables.
Using Rainwater in the Garden
Simply collecting rainwater isn’t enough; you need to make it easy to use. Install a spigot at the bottom of each barrel or attach a short hose to make filling a watering can more convenient. Elevating the tank helps use gravity to your advantage, increasing water pressure for faster flow and a more enjoyable experience.
For the tote tank, consider adding a drain adapter to the original outlet. The water tank system can be connected to a pump and garden hose. Repurpose a hot tub Flo-Master pump and use a hose long enough to reach every corner of your garden. This setup is particularly handy during dry spells and allows you to easily transfer excess rainwater to a geodesic dome greenhouse tank.
Self-Watering Rainwater Harvest
Having rainwater readily available is fantastic, but sometimes it’s useful to direct it to specific areas in your garden that need more water. This self-watering rainwater system allows you to irrigate perennials or food forests by collecting rainwater and letting the ground absorb it. However, it’s not ideal for vegetable gardens, as watering only occurs during rainfall. A well-mulched food forest, on the other hand, can absorb a large amount of water at once and then gradually release it to the roots.
Set up the barrel horizontally to serve as a buffer for the self-watering system. It only collects rainwater during heavy rain and releases it when the rain stops. Installed a 1.5″ hose in the patch and drilled 1/8″ holes every foot along the top. This creates a makeshift soaker hose that disperses water without any pressure.
A plug at the far end of the hose prevents water from flowing straight through. Place the hose alongside the plants you want to water, and make sure the holes are drilled evenly along the top so that the water flow matches the hose’s capacity.