Nine times out of ten, the first thing you consider when you bring a plant home is: How much water does it need? This topic is so ubiquitous that it coined the terms overwater-er, underwater-er, LECA-lover and hydroponic King or Queen, to name but a few.
This article is here to help you find your sweet spot. We will rank your indoor plants according to watering needs and touch on the difficulties of using hydroponics, LECA or soil as seasons change.
Houseplant water rankings
Some of this will come as no surprise, while others will be an eye-opener. Ranking houseplants from the ever thirsty “I could be a fish” to “Water, I think we had some last year” is a fun way to ease you into watering. The rankings reflect how plants compare to one another during the growing season (feel free to jump ahead and read more on why this is).
If I could swim, I would be happy
I like my roots being humid, thank you:
You can go on holiday for a week:
Don’t you dare bring that watering can near me without a water probe:
I like my mix with extra drainage, please:
These are broad categories that do not take into account the variation within a group of plants. Let me explain. A Monstera deliciosa often uses less water than a Monstera adansonii because the latter produces leaves at a faster rate (in my experience). The difference between them is less than between a Monstera and a Cissus.
Some species like high humidity around their roots, but would not tolerate sitting in water. Others may send out roots that dangle in the water without a care in the world. Their need for mist, consistent watering (but well-draining) or clear fresh flowing water comes from their natural habitat.
To learn more on tropical climates, see:
When is enough, really enough?
You have found yourself staring at that watering guide thinking: “What do they mean by medium water requirement? How can I water my plant to be a medium? Is it 500 ml or 1 L, please tell me? Should it stay wet for one, two or seven days? Should it stand in water?
Consider this: Indoor plants specialists will assume your indoor temperature remains at a balmy 20C, however, 98% of homes in South Africa will tend to be without consistent air conditioning (= no balmy 20C). This means your room temperature may dip to 8C or go as high as 35C. A single watering schedule would be ineffective in such a setting.
Dig into the article below for a few tips and tricks:
For every one plant, you may come across a hundred watering guidelines. Many may even contradict each other. Be sure to always look for the standards in your area. Failing any available info, try to remember what we will discuss in the following sections so you can apply it at home.
Consider the growing media: How much water does it hold?
Whether you use potting soil, vermiculite, sand or LECA, it all boils down to how much water and nutrients it can hold. More specifically, the ratio of water to air in your mix. Different soil components hold different quantities of water (some even hold on to nutrients). We would like to buy one soil mix and use it for everything, but you will soon find out that this means some plants will keep dying on you.
What to look for: When selecting your soil medium, look at their water holding capacity (%), porosity (%) or air space and cation exchange capability (CEC). The latter indicates if it holds only nutrients.
If you have a dry climate, you want to add things that hold onto moisture (high water-holding capacity). If a guide specifies “good drainage” is ideal for your plant, then make sure to look for both high moisture retention and porosity in the substrate. Mix and match till you find one that does not dry out too quickly but isn’t soggy for a week. Adjusting your soil accordingly will mean the difference between easy watering and constant checking. Here's a table below as a good reference to what to expect when buying soil.
Water-holding capacity, aeration and nutrient holding capactiy of five different growing media.
For more on soil guides and testing soil see:
Is hydroponics easier?
Hydroponics has been around since the 1970s and has seen newfound popularity in the houseplant market. It is by no means a new concept, but it is a field subject to state-of-the-art innovation. It gives the grower complete control over the plant, but “with great reward comes great responsibility”.
Definition: Hydroponics refers to the practice of growing plants in soil-free media. This includes coco coir (coco dust or fibre), expanded clay aggregates (LECA), rock wool or coco chips. The nutrients are delivered through constant exposure to water.
When you have so much control over a plants environment, you have to take into account even the smallest of changes. True hydroponic systems require heating in winter and may also require cooling in summer. Failing to do so will cause stress to the plant roots. Let’s take a quick look, shall we?
Root health and plant growth are affected by 1) the root zone temperature and 2) nutrients.
Things to consider:
- The optimal temperature around the roots is normally between 15-23 C.
- This may differ, with some preferring low temperature (15) and others higher (23).
- The temperature affects the availability of nutrients and oxygen.
- If it is too warm (>75F) the dissolved oxygen drops (not good).
- Colder temperatures will cause root damage and disease.
- Conversely, hotter temperatures may be heaven for bacteria.
- Nutrient availability is subject to the pH of the system.
- Unbuffered LECA tends toward alkaline pH causing nutrient deficiencies.
- Unsterile water with nutrients will recruit bacteria over time.
The past 40 years of hydroponics has taught us that not all plants can be grown in such a manner. The ones that do flourish and thus remains a feasible option for growing crops year-round.
I would note that researchers have found that hydroponic systems that make use of well water or acidified well water (<200ppm) have a problem with pH jumping from 6 to 8 after 4-6 weeks. This is avoidable when using purified water.
If you want to venture into hydroponics, J. Benton Jones released a Complete Guide to Growing Plants Hydroponically that covers everything you need to know!
Last but not least, make it easy on yourself. The experimenting is part of the fun and once you have your ideal mix it will be smooth sailing.
If you found the hints helpful or want to know more about a specific topic, let us know in the comments below!
Fields, J. S., Fonteno, W. C., Jackson, B. E., Heitman, J. L., & Owen, J. S. (2014). Hydrophysical properties, moisture retention, and drainage profiles of wood and traditional components for greenhouse substrates. HortScience, 49(6), 827-832.
Dusza, Y., Barot, S., Kraepiel, Y., Lata, J. C., Abbadie, L., & Raynaud, X. (2017). Multifunctionality is affected by interactions between green roof plant species, substrate depth, and substrate type. Ecology and evolution, 7(7), 2357-2369.
Langenhoven, P. (2017,). Characteristics of Soilless substrates [Presentation]. International Horticultural Conference, IHC2017. https://ag.purdue.edu/hla/fruitveg/Presentations/Langenhoven_Characteristics_Soilless_IHC2017.pdf
Pittenger, D. R. (1996). Ornamentals need balanced nutrition. Calif Fertilizer Assoc. May, 5-6. May 1996.
Jones Jr, J. B. (2014). Complete guide for growing plants hydroponically. CRC Press.