Bottom Watering Guide

Bottom Watering Guide

I used to think bottom watering was one of those overly fussy plant parent things. Like, why would I fill up a tray and wait around when I could just pour water on top and be done in thirty seconds? Then I bought a calathea (I know, I know), and within two weeks, the top inch of soil turned into this weird crusty layer that repelled water like a raincoat. I’d pour water in, and it would just run straight down the sides of the pot and out the drainage hole without actually soaking into anything.

That’s when I finally tried bottom watering. And honestly? It changed how I care for most of my plants. Not all of them, but a good chunk. If you’ve been curious about it or you’re dealing with soil that just won’t seem to drink up water anymore, this might help.

How to bottom water properly

The actual process is simple. You fill a container with water, stick your plant pot in it, and let the soil soak up what it needs from the bottom. That’s it. But there are a few things that make it work better.

First, you need a pot with drainage holes. This is non-negotiable. The whole point is that water travels up through those holes into the soil. If your pot doesn’t have drainage, this method won’t work. I learned this the embarrassing way when I tried to bottom water a ceramic pot I’d drilled a single tiny hole into. The water barely made it halfway up.

Pick a container that’s deep enough to hold a few inches of water but not so deep that your plant is swimming. I use old takeout containers, mixing bowls, or my kitchen sink if I’m doing multiple plants at once. The container should be wider than your pot so you can easily lift the pot out when it’s done.

Fill the container with room temperature water. I usually go about two to three inches deep, but this depends on your pot size. For a small four-inch pot, two inches is plenty. For a ten-inch pot, I go closer to four inches. You want enough water that it reaches the drainage holes but not so much that the pot is floating or water is splashing over the rim of the soil.

Place your pot in the water and wait. You’ll see the water level drop as the soil pulls it up. This is the part where you just let physics do its thing. The dry soil acts like a sponge, and water moves upward through capillary action (I looked this up after wondering how water defies gravity, and apparently it has to do with the way water molecules stick to soil particles).

Check the top of the soil every ten to fifteen minutes. When the surface feels damp to the touch, your plant has absorbed enough. This usually takes anywhere from ten minutes to an hour depending on how dry the soil was and how big the pot is.

Lift the pot out and let it drain. I set mine on a dish rack or in an empty sink for about ten minutes so the excess water can drip out. You don’t want your plant sitting in a saucer full of water afterward. That defeats the whole purpose and can lead to root rot.

Benefits for root health

Bottom watering encourages roots to grow downward instead of staying shallow near the surface. When you water from the top, roots tend to hang out in the upper layers of soil because that’s where the moisture is. But when water comes from below, roots have to reach down to get it. This creates a stronger, deeper root system.

I noticed this with my pothos. I have two that I got as cuttings from the same mother plant. One I top watered, one I bottom watered. When I repotted them a year later, the bottom watered one had roots that filled the entire pot evenly. The top watered one had most of its roots in the top half with just a few straggly ones near the bottom. The difference was obvious.

Bottom watering also reduces the risk of overwatering in a weird way. When you pour water from the top, it’s easy to just keep pouring without knowing if the soil actually needs it. You might think you’re giving it enough, but really you’re just creating a soggy mess at the bottom of the pot while the top stays dry. With bottom watering, the plant only takes what it can absorb. Once the top feels damp, you know the entire root ball is evenly moist.

According to research from the University of Maryland Extension, even moisture distribution is one of the most important factors for healthy root development. Roots growing in consistently moist (not soggy) soil develop better structure and are more efficient at taking up nutrients.

There’s less shock to the roots too. When you pour cold water directly onto soil, especially in winter, it can shock the roots. Room temperature water coming up from the bottom is gentler. I haven’t seen scientific papers on this specifically for houseplants, but it makes sense to me, and my plants seem happier for it.

Above: A close up look at the symptoms.

Preventing fungus gnats

This is probably my favorite benefit of bottom watering, and the reason I started doing it for almost all my plants. Fungus gnats are those tiny annoying flies that hover around your pots and make you look like you’re growing fruit instead of ferns. They lay eggs in the top layer of moist soil, and the larvae feed on organic matter and sometimes even roots.

Bottom watering keeps the soil surface dry. Since you’re not dumping water on top, that upper layer stays drier than the rest of the pot. Fungus gnats need moisture to lay eggs and for the larvae to survive. If the top inch or two is dry, they can’t complete their life cycle as easily.

I had a terrible fungus gnat problem last spring. I was watering everything from the top, and my apartment turned into a gnat convention. I tried sticky traps (which helped), I tried letting the soil dry out completely (which stressed my ferns), and I even tried that mosquito dunk thing (which sort of worked but was a pain). Switching to bottom watering made the biggest difference. Within three weeks, the gnat population dropped to almost nothing.

The North Carolina State University Extension notes that allowing the top inch of soil to dry between waterings is one of the most effective cultural controls for fungus gnats. Bottom watering does this automatically while still keeping the root zone moist enough for your plants.

You still need to let the soil dry out appropriately between waterings. Bottom watering isn’t magic. If you keep your pots constantly wet, you’ll still get gnats. But it gives you more control over where the moisture sits in the pot.

Fixing hydrophobic soil

Hydrophobic soil is when your potting mix gets so dry that it actually repels water. You pour water in, and it just runs off the surface or down the sides without soaking in. This happens with peat-based mixes especially. Peat moss, once completely dried out, becomes waxy and water-resistant. It’s incredibly frustrating.

I’ve dealt with this more times than I want to admit, mostly because I forget to water my plants when I get busy with work. I had a spider plant that I neglected for too long, and when I finally remembered to water it, the water just pooled on top and then drained out the sides in about five seconds. The root ball was totally dry.

Bottom watering fixes this. When you set the pot in water, the dry soil eventually has to absorb it because the water is in constant contact with the bottom of the root ball. It takes longer than normal (sometimes an hour or more for really hydrophobic soil), but it works. I’ve saved several plants this way.

For really stubborn cases, I add a drop of dish soap to the water. Soap acts as a surfactant, which breaks the surface tension and helps water penetrate the soil. Just one or two drops in a whole container of water is enough. I learned this from a hobbyist blog years ago and thought it sounded ridiculous, but it actually works. The University of California Agriculture and Natural Resources mentions surfactants as a solution for water-repellent soil in their guides, though they recommend horticultural wetting agents rather than dish soap. I use what I have.

You can also poke holes in the soil with a chopstick before bottom watering. This creates channels for water to move through and speeds up the process. Just be gentle so you don’t damage roots.

Above: The tools you need to fix this.

How long to soak?

This is the question I get asked most when I tell people about bottom watering, and the answer is annoyingly vague: it depends.

For most of my plants in four to six inch pots, it takes about fifteen to thirty minutes for the top of the soil to feel damp. My eight to ten inch pots usually need forty-five minutes to an hour. I have one massive fiddle leaf fig in a fourteen inch pot that sometimes takes ninety minutes if the soil was really dry.

The variables are pot size, how dry the soil was to start, soil composition, and even the shape of the pot. Tall narrow pots take longer than short wide ones because the water has farther to travel.

You’re looking for the surface to feel moist but not soaking wet. Stick your finger on top of the soil. If it feels damp and cool, you’re done. If it still feels dusty dry, give it more time.

I check every fifteen minutes or so. I know some people who just leave their plants soaking for an hour and call it done, but I’m paranoid about overwatering. Checking lets me pull the pot out as soon as it’s ready.

If you forget about a plant and it soaks for too long, it’s usually not the end of the world. Just make sure you let it drain really well afterward. I’ve left plants in water for a few hours by accident (usually because I start bottom watering and then get distracted by dinner or a work call), and they’ve been fine as long as I don’t let them sit in a puddle once I take them out.

Some plants need longer soaks than others. My maidenhair fern drinks like it’s at an all-you-can-drink buffet and takes forever. My snake plant barely needs ten minutes because it doesn’t want much water anyway.

The first few times you bottom water a plant, pay attention to how long it takes. After a while, you’ll get a feel for it. I know my calathea takes about thirty minutes and my monstera takes forty-five. It becomes routine.

One thing I’ll mention is that you shouldn’t bottom water every single time if you live in an area with hard water. Minerals in tap water can build up in the soil over time, and when you bottom water, those minerals concentrate near the surface as the water evaporates. I flush my plants from the top with fresh water every third or fourth watering to wash those minerals through. It’s a balance.

Bottom watering isn’t something you have to do for every plant or every watering, but it’s a useful technique to have in your toolkit. It’s especially helpful for plants that are prone to overwatering issues, for dealing with gnats, or for when your soil decides to stage a rebellion and refuse to absorb water. Give it a try next time you water. You might be surprised at how much easier it makes things.

References

North Carolina State University Extension. “Fungus Gnats.” NC State Extension Publications.

University of California Agriculture and Natural Resources. “Managing Water-Repellent Soils.”

University of Maryland Extension. “Watering Houseplants.”