Top Watering vs Bottom Watering
It doesn’t matter where you get the water from as long as it goes to your plants, so long as you give them enough.
However, some plants are more sensitive, so some plants prefer one method or the other. African violets don’t enjoy getting their leaves wet, so bottom-up is the best way to go.
I have found that each method of watering has its pros and cons, and the method I use depends on a number of factors, including the plant, my time frame, how eager I am to water, and how sick I am of fungus gnats at the time.
A watering can (or a teapot in my case) is used to water a plant from above. You apply the water through the leaves so it hits the root system without spraying water everywhere.
Make sure the top of the soil is completely saturated before running it under water until it runs out of the drainage hole at the bottom.
Drain the water away and do not allow the plant to sit in the liquid that has already travelled through the pot. This can cause your plant to reabsorb some salts and minerals it needs to be free from.
Top Watering: Pros
Top watering is usually a waste of water (more on that later), so I do it for plants which need watering urgently and can’t be taken care of right away.
Your plants should not require so much watering if you are taking care of them well, right?
That is true in most cases – drooping plants will be fine for a while until you have time to take care of them, but some plants, such as alocasia, require additional water while they are waking up.
Those plants need watering almost daily, so it’s easy to let them go. However, if they’re never watered there’s a chance that leaf won’t develop properly.
When you top water, you can literally wash away pests since the eggs and larvae develop in your soil and are sent down the drain.
Just don’t let this be the sole reason you water topically. Top watering can also increase pests and bugs, so you can’t have it all.
Diminish mineral deposits
Mineral deposits and salts will accumulate over time in your soil. If you have terracotta pots, you can see them building up on the sides.
Some of these may result from the fertilizer you use and the water you use – those of you living in hard water areas will probably see more. You might find it beneficial to collect rainwater or to purchase a water filter.
Top watering thoroughly removes salt and minerals, which is why it’s important to let excess water drain away and to not leave your plant standing in water – you don’t want it to reabsorb those nasties.
You might have brown tips on your leaves because of mineral deposits built up in the soil.
The plant is thoroughly soaked
You know that every inch of your plant’s soil will be wet as long as you water it thoroughly and properly. Well, more or less.
A plant can be hydrophobic over time, which means that water runs out of the holes in the bottom of the pot, not through the soil. Bottom watering is a great way to make a plant non-hydrophobic.
Top watering: cons
When it comes to watering houseplants with the top on a stand, there are two pretty big downsides. However, neither of them is life-threatening to your plants (apart from a few very specific circumstances).
Damage to the leaves of your plants
There are many plants that don’t like having their leaves wet. In fact, few plants like having their leaves wet. However, this isn’t usually a big deal because in nature plants have to deal with rain. As a result, plants have learned to adapt to occasional rain without dropping leaves immediately, because rain does not try to avoid plant leaves AT ALL.
Even so, I must mention that certain plants won’t tolerate water much at all, for example Africa violets will rot easily if water is sprayed on them without care. You see, heat is a huge factor in the parts of Africa from which they originate, so either it’s too hot to get rain for months at a time or the rain evaporates very quickly.
Encourage fungus and pests
When I started bottom watering almost exclusively, I observed a significant decrease in fungus gnats.
Some pests like damp conditions, such as fungus, fungus gnats and a few others. To keep them out I keep the top couple of centimeters of the soil dry.
If an outbreak of fungus or pests occurs when watering exclusively on the top, it is usually a sign of an underlying problem – overwatering.
Nevertheless, if your wine glass holds a substantial amount of gnats but you’re not experiencing a massive infestation, you may find bottomwatering to solve your problem.
It won’t solve the problem, because fungus gnats are nearly impossible to eradicate, but it will at least keep the population low.
Soil become compacted
It is important to note that water is heavy. If you keep putting a lot of it on top of the soil it can cause it to become compacted, which is bad in a number of ways:
Water always tends to flow down the easiest path in the soil. This means if the soil is very compacted, it’d run down the gap between the soil and the side of the pot, instead of evenly through the soil.
If the root system becomes too compacted, it may cause damage. Roots prefer a bit of air movement around them, so they can become damaged (or even rot) if the soil becomes too dense.
If you’re concerned about compacted soil, you should take the following steps:
A fork (or moisture probe) can be used to gently agitate some of the potting mix.
Usually, most commercial potting mixes are heavy, so repot your plant in a mixture of your regular house plant potting mix, perlite, and bark chips. I use 2 parts house plant potting soil to one part perlite, and one part bark chips.
Do not worry too much about soil compaction if you can only top water – make sure you have a nice, airy soil mix, and give it a good shake from time to time.
The easy way, for the time poor
Make sure all of your plants have:
a) some drainage holes in the pots
b) a saucer beneath the pot to be filled with water.
Put a bit of water in the saucer. Wait for it to empties. If not, add more to it. If you suspect the plant is still lacking water, poke it with your trusted moisture probe. Or just keep adding more until the water stops draining.
The also easy, but more time-consuming way
Taking this approach ensures that everyone gets good soaking, but it can be a bit time consuming and annoying.
Bottom Watering: Pros
It doesn’t damage the leaves
It may be worthwhile for you to try bottom watering if you already overwatered your plants in the past, and have scraggy leaves to prove it.
Do some research if you’re unsure whether your plant will tolerate wet leaves. Plants that come from one of the desert environments have a lower tolerance for damp leaves than plants from the tropics.
The leaves aren’t technically leaves, but a cactus will rot rapidly if you regularly water it.
The top of the soil remains dry, discouraging pests
Pests like the damp. Not just fungus gnats – spider mites love them a bit of wet soil.
Encourages the roots to spread out and get stronger
When the roots of your plants have to work to steal moisture from the air, they are more likely to grow stronger and reach the bottom of the pot more quickly.
Plants like succulents and cacti mimic their natural environment with this method – they often grow in areas with little rain so their roots must grow toward the groundwater.
It’s more difficult to over water
It is possible to overwater your plants, but not likely unless you keep them constantly topped up.
Even a small bowl and bottom watering can drastically improve your plants’ chances of survival if you’re a serial overwaterer.
Even with the saucer filled completely, and every day, it is unlikely you will overwater, since you can only fill it up to a tiny amount. Unless your plant is similarly small.
Bottom Watering: Cons
Mineral and salt deposits can build up
Mineral deposits can cause the roots of your plants to be burned if they cannot be flushed through with water from the top.
You can set yourself a reminder to top water everyone every three months or so if this is something you want to be aware of (say, if you use tap water and it is particularly hard).
In the event that you fertilise your plants, one idea might be to top water your plants after each feeding so that you associate both with each other and are less likely to forget.
It’s a pain for big plants
It takes a long time for large plants to absorb enough water, especially if they’re in terracotta pots. They’re hard to move to the sink and creates a mess.
It takes longer
Well, it depends on what you have set up. If you have only small saucers, it can be time consuming to go around filling them up, and then emptying them when the plants are sufficiently hydrated.
It can be messy
The water or soil (but probably both) will get all over the house when you’re moving plants back and forth from soaking trays.