One Tablespoon A Day - Watering house plants may require less than you think.

A little more than a tablespoon a day, to be more precise, but that is all the water that is possibly needed. This was quite an intriguing revelation. The most common question in plant maintenance is: how much water and how often? The ambiguity around volume and frequency appears to be the number one reason why people describe themselves as plant killers. But here it was—a neatly packaged answer of 21.26ml per day.

I should tell you that the study I was reading about was conducted by researchers from University of Georgia and University of Maine, in a commercial-style greenhouse, on petunias grown in 10cm pots from seedlings in a peat-free substrate. The aim of the grower was to achieve maximum growth and health while preserving the precious resource—water.

In my search for other reference points I was surprised by how little research is done in this area. Many of the articles and papers I’ve come across focused on commercial and agricultural growers, mainly discussing watering methods to achieve the healthiest plants rather than the amount of water needed for good results.

1. Stars Unite Europe, a group that focuses on growing poinsettias, recommends using 10-20ml for a 6cm pot, 100ml for a 13cm pot, and 10-20% pot volume for large poinsettias (no pot size specified). Unfortunately, there is no recommendation regarding frequency.

2. BAC Fertilizers, a Dutch company, recommends using 5 to 10% of the pot contents. I will be using 7.5%. For a commercial 10cm pot (400ml) 7.5% is 30ml per pot. Not too far off from the poinsettia team, but again, no specification if it is a weekly or daily amount.

*Based on commercial 10cm pot = 400ml. Amount of water = 7.5% of 400ml = 30ml

3. Canna, a Dutch company specializing in fertilizer and growing media, suggests a general rule of thumb for determining the irrigation needs for healthy roots: For one square foot of leafy area, use 4-6L (4000-6000ml) of water per day. For new plants or if the square foot is not completely leafy, use about three litres per day on average. This is true whether you have two plants or twenty in that square foot.

   
   

   I can fit 9, 10cm pots in one square foot. I'm using 5L a day for 10 pots equals 555ml per pot per day. Seems rather a lot by comparison.

*1 sq foot = 9 x 10cm pots approx. **Based on commercial 10cm pot = 400ml. Amount of water = 5L/9 pots = 555ml

4. Microdrips, a Canadian company, suggests 2.5cm of water in height. They give an example of a 30cm x 30cm surface area requiring 2.25L (2250ml) per week. Following their maths, a 10cm pot requires 196.35ml per week, or 28.05ml per pot per day.

*Recommendation given 2.5cm height of the growing area, example provided 30 x 30 x 2.5 = 2.25L / week. **Using source’s example, 10cm pot area = 78.54 x 2.5 = 196.35ml / week. Amount of water = 196.35ml / 7days = 28.05ml

Of course, these figures in no shape or form reflect our homes. Still, it is fascinating. If certain plants require as little water as 21.26ml/day, it certainly explains why so many of us overwater our flora.

So…is a tablespoon enough for watering house plants? How far does a tablespoon of water stretch in a domestic setting?  And is it even possible to determine a good guidance with regards to how much water (number of ml) and how frequently (number of times a week) a specific plant species require in a home setting?

Essentials For House Plants Watering

The Fazeley Flow

Haws Watering Can

Small, but big, watering can for pinpoint watering accuracy. And if the research is right, it can water 27 plants in one go!

Volume: 1 Pint / 568ml

Dimenions: L31 x W11.5 x H11

Made in UK 

£45.00

Welcome to The Plant Notebook

My name is Anna and I'm a maker with an interest in plants. I run Horticus from my pottery studio in Leicester where I make my living wall kits, write about indoor gardening and dabble in fun experiments.

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