To water or not to water?
That is the question asked by many a gardener, their watering can hovering over a stubbornly mute Aspidistra which refuses to reveal whether it’s thirsty or not! “When did I last water it?” you ask yourself. “Last week? Last month? ….Last year?” At this point you are pondering the possibility of encroaching dementia as your watering recollections have merged into a dense fog. “How often am I supposed to water this thing anyway?” you wonder, dashing to look it up on Google. “Every week”, “Every other week”, “Every few weeks”; the answers are as varied as the water stains on your furnishings which you are now eyeing up crossly. Clearly, your inability to divine your Aspidistra’s needs must be down to an absence of those mystifying ‘green thumbs’ and you splurge a glug of water into the saucer ‘just for good measure’ before stomping off to quench your own thirst with a cuppa.
Sounds like a familiar story? Well, sit back, enjoy your tea and I will attempt to clear the muddy waters around this critical topic.
Rule of Thumb
Your friend may provoke garden envy with her lush urban jungle of tropical houseplants, but this is not down to an innate gift for communicating with the plant world. Having ‘green thumbs’ is not a special talent, but simply the application of a skill which all of us already possess: observation.
All you need to do is ‘get your eye in’ and regularly observe the condition of your plants, their environment and the relationship between them. This is the key to successful watering.
A Potty Problem
All houseplants come in pots. This unremarkable fact is crucial to appreciating why watering is a skill and why the incorrect application of water is the most common cause of death for houseplants.
The Root of the Issue
A pot is an entirely unnatural environment for a plant and makes it especially vulnerable to watering errors. Contained within a pot, the roots of a plant are restricted from following their natural growth pattern. Plants may have a constricted root ball which is less able to take up water and nutrients. They aren’t able to search for water during dry periods and are entirely reliant on your care.
Conversely, the root ball may be too small for the pot and surrounded by sodden compost. This is particularly the case for epiphytic species such as Orchids, Anthurium and Bromeliad. In their natural habitat, these plants do not grow in the ground. Instead, they attach themselves to the branches of tropical trees where their exposed roots are lavished with high aerial humidity. These roots will not appreciate being surrounded by soggy, airless compost and they are especially susceptible to overwatering.
Meanwhile, other plants simply can’t stretch their roots in the direction they would wish when they’re trapped in a pot. For example, most ferns like to grow their roots outwards rather than downwards, but pots don’t permit this to happen.
Drainage is essential!
The way water behaves in a pot is quite different to the open ground where water disperses through natural drainage channels. For this reason, pot plants can quickly become saturated after watering. It is essential to use pots which have plenty of drainage holes. If you are recycling containers make sure that you drill or punch holes in the bottom. To prevent ruining your furnishings you will need to use a saucer with your pot. When you water, allow the water to drain through and then empty the saucer shortly afterwards. Never leave your plant to sit for ages in a saucer full of water – this is a reliable way of killing it!
If you have a stylish pot which you don’t want to spoil with a saucer then grow your plant in another pot which sits inside. Whilst it isn’t impossible to grow plants in pots without drainage holes, it makes managing water very challenging.
Also ensure that you are growing your plants in the correct medium. Most houseplants require coarse, free draining compost and dry-loving species such as Cacti and succulents will require plenty of grit. Epiphytic species need a soil-less potting mix which is composed of coarse materials such as bark.
How Often Do I need to Water My Houseplant?
There is no secret formula for how often to water your houseplant as there are so many variables which can affect watering requirements. Although it’s possible to give rough rules of thumb which indicate the watering ‘tolerance’ of a plant, ultimately it comes down to your observation skills!
Watering Frequency Checklist:
Plants with fleshy, thick, hairy, waxy or smaller leaves/stems will all dry out more slowly and tolerate drier conditions. A larger leaf surface area – either larger individual leaves or a dense canopy – will lose water quicker.
A congested root ball in a small pot will dry out quicker and be harder to rehydrate. Plants with poor or immature root systems need watering with care as they are easily over-saturated.
The material of your pot will have a significant impact. Clay pots are porous and will rapidly suck water out which is then lost through evaporation. This can mitigate over watering. If you overwater a plant in a glazed pot, then the plants roots are likely to remain saturated for a long time.
Where your plants are growing will directly influence their watering needs. Plants placed on a sunny south-facing window sill will dry out much quicker than those in north facing rooms. In winter, plants may dry out quickly if they are positioned close to central heating. Arranging plants in a group can increase local humidity so plants will dry out more slowly.
Time of the Year
In the winter, lower light levels and cooler conditions cause growth to slow down and plants will undergo a resting period during which they should be kept drier. However, if you have the heating running all day make sure your plants are not becoming desiccated.
In spring, plant growth accelerates, and you can begin to water and feed them more. Watch the growth of your plant and water accordingly.
How do I know if my plant needs watering?
Four basic watering rules:
1. Give the compost a prod
Stick your finger into the compost as far as possible and check the moisture level. Be aware that the surface of the compost might be dry whilst the bottom of the pot remains wet. Pick up the pot and look underneath. Is there moisture on the bottom? Does the compost you can see in the drainage holes look dark and moist? If you are still unsure you can gently tip the plant out of its pot and inspect the root ball for moisture.
2. Check the Weight
Pick the pot up and judge the weight – you will quickly become accustomed to knowing the difference between a pot which is full of moisture and a dry one.
3. Allow the compost to dry out between waterings
Houseplants don’t enjoy constantly sitting in wet compost. Allow the compost to dry out a bit between waterings.
4. Don’t wait until the plant looks sick
A sick looking plant isn’t necessarily a plant which needs watering!
Is my plant underwatered or overwatered?
The difference between an underwatered and overwatered plant may not be immediately apparent. Plant roots are covered in tiny ‘root hairs’ which is where most of the water is absorbed. Overwatering causes these tiny hairs to die and so ironically, the plant can no longer take up water! The plant is also deprived of oxygen because in saturated conditions all the air spaces in the compost have been displaced by water.
If overwatering occurs, leaves will go brown at the edges and fall off, growth is poor, and eventually the whole plant will collapse into a sorry mess. Signs which all look confusingly similar to an under watered plant.
As a result, a common mistake when confronted by a brown, crispy or collapsed plant is to splurge water onto it. Resist this temptation. Always examine the compost first and, if necessary, the root ball. If the compost is already wet and/or the roots brown and rotting, then you know the problem is overwatering.
If you have overwatered your plant, then deliver emergency aid quickly! As soon as you realise your mistake, carefully remove the plant from its pot and sit it on a heap of newspapers to dry out the root ball.
Other signs of overwatering
- Mosses, liverworts or moulds on the surface
This is a sure sign that you are overwatering your plant. Stop! Dry out the root ball.
- Sciarid fly
Have you spotted those annoying little flies scurrying over the surface of the compost? These are sciarid flies and they love moist compost, so you are probably overwatering your plant.
Avoid potting up your houseplants unless they are becoming pot bound. Remember – aside from aquatic dwellers or bog-lovers, plants do not enjoy having their root ball sitting in a large mass of soggy compost. Moreover, plant roots resent disturbance, and no matter how careful you are, repotting will cause some root damage. After repotting, plants tend to stagnate for a while, and root growth is halted. This effect is called transplant shock. Plants suffering ‘transplant shock’ are not in active growth and will be even more sensitive to sitting in over-saturated compost.
Routinely observe the condition of your plants leaves. The first signs of underwatering are lack of ‘turgidity’ in the leaves. Simply put, the leaf cells are no longer plumped up with water. With thin leaved plants the leaves will drop and the whole plant will collapse quickly if underwatered. However, many houseplants are equipped with a tough outer ‘cuticle’ to their leaves and stems so the signs are more subtle. Look for a wrinkled appearance to the outer surface of the leaf. The leaf will start to soften and be less taut in appearance. As it dries out further, it will pucker and curl with the edges becoming dry and crisp. You’ve done your observational ‘detective work’ properly when you’ve checked the compost. If these symptoms are occurring and the compost is dry, then you know that the problem is underwatering.
The good news is that if you notice these signs early it is possible to save your plant. If the compost is completely dry it can be hard to rewet. In which case, plunge it into a bowl of water to rehydrate it. Even if the whole plant has collapsed the leaves will quickly pop back up again. Any shrivelled leaves can be cut back or pulled off and the plant left to regenerate new ones.
Overwatering tends to be more fatal because the death of those delicate root hairs is irreversible. This is why, when you are honing your watering skills, it is often better to err on the sign of caution.
However, although plants will generally survive bouts of drought, routine underwatering makes them feel and look stressed. Before long, aphids and other unpleasant critters move in because like humans, stressed plants are much more susceptible to pests and diseases.
Watering is a skill, but one which anyone can master. It’s all down to observation over time. Rather than thinking of a weekly ‘watering routine’, get into the habit of a weekly ‘plant check’. Spend some time in your plants company and get to know them! Observe their overall appearance, the condition of the leaves and check the moisture level in the compost. Your houseplants will be much happier as a result.
Head to our dedicated houseplant hub page for more top tips on caring for your indoor plants.
Annelise Brilli is the Horticultural Copywriter for Thompson and Morgan. Annelise caught the gardening bug from her mother, whose tiny backyard was crammed with a huge collection of plants. As an adult, she had a career change into horticulture, gaining a training apprenticeship with the National Trust at Powis Castle Garden in Welshpool. She went on to work in a range of private and public gardens, later running a garden design and maintenance business. She is passionate about sustainable gardening and has developed her own wildlife-friendly garden which she has opened as part of Macmillan Coastal Garden Trail.