Light and water: Striking the balance for healthy house plants

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Written By Martin Cole

Plantsman, gardener, plant-obsessive

light and water for house plants

Why you should water your house plants according to the light levels available.

Light and water are probably the two most important factors when it comes to basic house plant care.

The amount of light your houseplants receive directly influences their need for water.

If you think about it, you don’t get as thirsty after sitting quietly indoors as you would after exercising in the hot sun. In the same way (sort of), plants require a tailored approach to hydration based on their exposure to light.

light and water for house plants

Light fuels the growth and health of your houseplants through photosynthesis. When the amount of light increases, so does the plant’s need for water, as it is actively engaging in growth and energy conversion.

On the other hand, in low-light conditions, plants slow down their metabolic functions. This means you need to water them much less, or risk creating waterlogged soil that can lead to root rot.

Light and water: Key points to remember

  • Light levels significantly affect how much water your houseplants need.
  • Adapt your watering according to the intensity of light that particular plants receive in order to promote healthy plant growth.
  • Be mindful of overwatering and underwatering to protect your houseplants from stress.

The science of light and plant growth

Understanding the role light plays in the development of your house plants is crucial.

For plant parents, the key point is that it’s not just about providing light and water.

You need to ensure ensure you strike the right balance between light and water to optimise your plants’ health and growth.

In order to understand why this matters, we need to know a bit of plant science – in particular the bit about photosynthesis.

light and water for house plants image

Understanding Photosynthesis

Photosynthesis is the extraordinary process by which your plant converts light, water, soil nutrients and carbon dioxide into:

  1. glucose, which fuels the creation of new cells and, therefore the growth of new roots, stems, leaves and flowers; and
  2. oxygen, which is released as a by-product (and represents one of the health benefits of plants.

At the heart of photosynthesis is chlorophyll. Chlorophyll is the pigment that gives plants their green colour. It is found in chloroplasts, which are specialised organelles found in the cells of leaves and stems.

Chlorophyll allows the plant cells to absorb light efficiently. Without sufficient light, your plants cannot perform photosynthesis effectively.

Light intensity and quality

Your plants’ light requirements vary according to the conditions found in their natural habitats. But one rule remains—light intensity directly affects the rate of photosynthesis.

Higher light intensity boosts the production of glucose and energy, contributing to vigorous growth.

However, there is a limit to this. Where a plant is exposed to a level of light intensity beyond its natural range, its leaves can be scorched and the photosynthesising cells damaged, ultimately killing the plant.

This can occur when you expose a plant to higher light intensity, when either:

  • it is naturally not adapted to high light intensity at all, or
  • it could adapt if exposed gradually, but you have not given it enough chance to to do so (for example by increasing the time each day you expose it to brighter light).

Conversely, in low light, plants may struggle, becoming leggy as they reach for light, especially if they are naturally adapted to brighter conditions.

Quality of light is also important; different wavelengths influence various growth stages, so ensuring your plants get a broad spectrum light can lead to better health and vitality.

The simplest advice is to be aware of the light levels across different parts of your home to match plants with their ideal conditions. Make sure you note how light levels change during the course of each day, and over the course of the seasons.

Watering techniques by light level

light and water
Light and Water

Adjusting your watering strategies to the light levels directly affects your house plants’ health. It is, therefore essential to find the right balance to avoid overwatering or under-watering.

This, as we have seen, depends to a significant extent on how much light your plants receive.

It also depends on the seasons, and whether your plant is actively growing or not. As a general rule you need to reduce watering over winter when the plant is dormant.

Assessing soil moisture

Before watering, check the soil moisture. An easy test is to push your finger down into the soil as far as it can go; if it’s dry, it’s time to water.

Watering and light exposure

Indoor plants in brighter areas typically need more frequent watering, as the soil dries out more quickly. This is due to increased evaporation and the rate at which the plant is photosynthesisingand using the available water.

Conversely, plant in low light need less water, as the soil stays moist longer.

As ever, though, it is not quite so straightforward as this.

Plants that thrive in direct sunlight, such as cacti and succulents, are naturally adapted to require less water, because of the drier conditions in their natural environments. You therefore need to be sure you don’t over-water those kinds of plant.

Learning from houseplant varieties

Different plants have varying water needs; some thrive in moist soil, while others prefer drier conditions.

Of course, you need to find out the basic needs of each plant you grow. But is is also important to observe and learn how your houseplants react to different watering schedules and sunlight exposure in the conditions in your home. You can then make adjustments accordingly.

Matching your house plants to your lighting conditions

When growing houseplants, it is vital to matching the specific light requirements of the plant species to the light levels in your home. It is therefore important to understand which plants thrive in low, medium, or bright light.

Low light houseplants

In low-light conditions, such as those found in rooms with north-facing (in the northern hemisphere) or obstructed windows, certain plants not only survive but flourish. Ferns and philodendron are excellent choices for these areas. They require less natural light to carry out photosynthesis compared to other plants.

Pothos are also known for their adaptability in dimmer spaces, with their trailing vines making them a visually appealing option for less sunny spots.

  • Examples of Low-Light Houseplants:
    • Ferns
    • Philodendron
    • Pothos

Medium and bright light houseplants

If you have east-facing or south-facing windows (in the northern hemisphere) providing medium to bright light, your options for houseplants broaden considerably.

Orchids are medium light lovers that provide a tropical flair to your space. Meanwhile, succulents and cacti demand a spot in your brightest, sunniest windows.

These plants have adapted to more intense sunlight and need these conditions to maintain their health and growth.

Remember, though, even sunlight-loving plants can experience too much of a good thing, so observe for signs of scorching or bleaching, and consider supplemental artificial lighting if natural light is insufficient.

  • Examples of Medium to Bright-Light Houseplants:
    • Orchids (Medium Light)
    • Cacti (Bright Light)
    • Succulents (Bright Light)

Light and water: the summary

The key thing that I want you to take away from this post is that light and water are interdependent when it comes to house plant care.

The general watering advice, which you will find on this website and elsewhere, such as ‘requires moderate watering’ is only the start. You need to also consider how much light the plant is getting and adjust the amount of water accordingly.

The Sansevieria (Snake Plant) is a good example to work with here because it is a plant that can handle different light levels. That means that you might well have two Sansevierias, one near the window and one in the shadows some way back in the room.

In that case, you would need to make sure that don’t automatically give both plants the same amount of water at the same time. The Snake Plant in the light will definitely dry out more quickly and more frequently than the one in the shadows.

So what you need to do is observe for yourself exactly when each plant needs watering and work on that basis, rather than on a regular schedule.

As with with most things plant related, it is all about getting the balance right.

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