The Benefits of Rainwater

by Kealey Bacic 

Kealey has her own business, Iron Ivy (https://ironivy.com.au) where she spends her days designing homewares inspired by the natural world and is a horticulturist dabbling in greenhouse jungles. 

Hey Ma! The rains are ‘ere! Australia’s east coast has been experiencing a once in a lifetime amount of rain in the last few weeks so it’s a great opportunity to look at some of the benefits of this water and how we can harness it. Light and water are the life force of plants. Plants have a remarkable ability to turn energy from the sun, with a few added nutrients mixed in with water into matter.But did you know that the type of water you use can offer some very different outcomes for your plants? While most plants are perfectly fine with tap water, rain water is beneficial in many ways. Some magical reactions happen with rain water that can provide your plants with a little boost of life!Have you ever noticed how the grass looks greener after a heavy rain? Your garden looks happier and more lush than before? Here’s a few reasons why plants benefit from a heavy drench of water straight from the sky.

Nitrogen - this element plays a major part in chlorophyll and protein production in plants which allows them to photosynthesise and grow larger. The Earths atmosphere is made up of 78% nitrogen, however nitrogen in this form isn’t able to be used by plants - lightning storms and beneficial bacteria living in the soil and in roots of plants ‘fix’ this gaseous nitrogen into a form that can be readily absorbed by plants (ammonia & nitrates). When it rains, atmospheric nitrogen is brought down to the earths surface and is abundantly available to these nitrogen fixing organisms or has been fixed by lightning that often accompanies rain.

CO₂ - when carbon dioxide is mixed with water and other minerals present in rain water is becomes carbonic acid. This diluted acidic solution helps to maintain a slightly acidic soil which is generally favourable to most plants. The majority of houseplants prefer a substrate pH between 6-7, an ideal pH allows macro-nutrients present in the soil such as copper, manganese, iron and zinc to be “unlocked” and easily absorbed by the plant.

Deep watering - consistent rainfall will evenly drench the soil and reach parts of the roots that may often be deprived of moisture or experience dry pockets from hose or sprinkler watering. This deep watering encourages roots to extend further as they sense more viable substrate to grow into. More roots means your plant can take up more nutrients and grow healthier and happier!

Leaf cleansing - anyone with indoor plants, I’m sure you’re well aware that sometimes plants seem to be dust magnets, gathering a fine layer of dust (or thick if you’ve been a little neglectful...no judgement here!) on their leaves. Besides making your plant look dull and potentially causing sneezing fits every time you walk past it, the dust actually hinders the plants ability to photosynthesise. The reason plants seem to attract this dust is because they transpirate - that is water moves through their system from the roots and is excreted through pores in the leaves - this moisture makes dust settle and stick to the surface and after a while can make a happy plant turn sad. Putting your plant out in the rain for a while will rinse the leaves and give them the best opportunity to absorb all the sunlight they need to thrive.

Flushes salts and minerals - have you noticed a crusty white ring around your terracotta pots? Or maybe white patches on your leaves, this is a buildup of salts and minerals. Tap water contains many minerals that are intended to improve the quality for human consumption, these minerals in high concentration can make the water “hard” which can have a number of effects on our skin, plumbing and other things it comes in contact with, to counteract the hardness of water sodium is added. These minerals and salts are fine for most plants but can build up in your pot or garden bed and cause problems down the line. Rain water helps to flush this build up from the roots zone of your plants and give them a fresh substrate...I imagine it’s the plant equivalent to that feeling you get when you put on a fresh pair of brand new socks.

Higher oxygen content than tap water - if you’re a plant parent to one plant or one hundred plants, chances are you’ve experienced root rot from over watering. Root rot after heavy rain is much less likely to occur due to the higher oxygen content in rainwater which acts as a “safety net” for the root zone. This higher oxygen content also assists beneficial microorganisms in the soil to be able to “breath” and continue their important ecological processes.

So next time there’s a heavy downpour near you, especially if there’s lightning about, grab your buckets and watering cans or take your plants outside for a shower in the good stuff! Your plants will love you for it plus you’ll save a little on your next water bill as an added bonus! Yay for rain!