Bottom watering plants – why, when & how

Your seeds, seedlings and plants do not really ask for much. Light, nutrition, a growing medium, air and water. Here today we will look at how bottom watering plants can help you care for your plants and herbs better.

Bottom watering plants is a technique which has been used for decades and it does not only apply to hydroponics (soilless growing mediums such as coco, rockwool or perlite) but also applies to germinating seeds and planting out seedlings and mature plants in soil.

We will look at bottom watering seeds and seedlings as well as more mature plants. Because just as different types of plants have unique needs you also need to factor in the age and stage of development of your plants.

What is bottom watering?

Bottom water pots or peat pellets
Bottom watering peat pellets also works well

Everyone is familiar with top watering where watering cans are used to water the pots from above. Bottom watering is basically a form of reverse watering.

With the bottom watering method you put pots with drainage holes in a container partially filled with water for the soil to absorb the water it needs.

Whereas bottom watering is quite common for houseplants is is less used for outdoor pots with herbs and vegetables.

And I have never really understood why houseplant care would be different to looking after pots with, for example, herbs or tomatoes.

How to bottom water pots

Bottom watering is a simple method especially good for smaller plants and pots. Larger plants are more difficult to water as they are heavier to lift and require a bigger container.

Follow the 4 steps below to master the art of bottom watering like a professional.

1. Partially fill a container with water

Fill the container with a minimum of 3 cm (at least an inch) of water. For larger pots you will of course need to add more water (up to 10cm or a few inches).

If the tap water in your location is rich in chlorine you should consider using distilled or filtered water. Signs of chlorinated water are cloudy or hazy water, any discoloration of the water or strong smell.

2. Place the pots in the container

Make sure to provide proper support. You do not want the plant to fall over. Now step away and let the plant sit and soak in the water.

3. Check moisture level every 5 minutes

Remove pots from the container when the soil’s surface is moist or changes color. From my experience medium sized plants need about ten minutes to soak up enough water.

4. Remove the pots from the container

Place plants in a sink or an empty container to allow any excess water to run off.

Using a sink is easier but if using an empty container I recommend putting a layer of LECA pebbles in the bottom to keep the pots dry. Place pots back on their saucers after a few minutes.

3 Advantages Bottom watering plants

1. Prevent flooding of seeds and seedlings

Most people use a regular watering can when top watering pots and plants. You may or may not have a rose (like a shower head) on your watering can to gently spread the water.

Still, you may find that if you pour too fast even what may seem as the smallest amount of water can overfill smaller pots. The potting mix will soak up water but not fast enough and water spills over the edge.

And when this happens to seeds and seedlings you risk displacing seeds and the young developing roots of seedlings.

The water you add risks shifting the soil and as seeds and roots get flooded and start floating around.

When you instead water pots from the bottom the surface of the soil is left moist but intact and undisturbed.

2. Bottom watering helps find correct level of moisture

Top watering is easy and convenient but it is not very exact.

When we water using a watering can it is difficult to know when the the potting soil reaches the correct level of moisture throughout the pot.

And we don’t want to water too much. Or equally bad, not enough.

When you water pots from the bottom the soil will soak up as much water as it can hold. And any excess will run off as you remove the pots from the container. 

You will know that you have reached the correct level of moisture throughout the pots when you see the surface of the soil changing color.

Still you should check on your pots every 5 minutes or so to avoid overwatering the pots. The excess will run off but overwatering is never healthy for a seed, seedling or plant.

Overwatering soil can also lead to problems with pests and diseases like for example fungus gnats and leaf miners.

3. Bottom watering pots will not compress soil of potted plant

Root systems need water to develop. This is true for seeds, seedlings as well as established plants. But they also need air or oxygen. 

Have you ever noticed that fresh soil tends to shrink in volume as you water the pot? Watering pushes the air out and makes it more compact..

Top watering seeds, seedlings and plants will over time compact the soil making it harder for the plant’s roots to develop.

Bottom watering plants will on the other hand never create this downward pressure as it is the soil that soaks up the water.

You are not adding water to the pot. You are making water available to be absorbed.

Why Bottom watering is better than top watering

Top watering is by far the most commonly used methods for watering pots and plants. 

The general principle is to water from the top. And watering at the base minimizes the risk of wet leaves that can invite pests and fungal diseases.

When the water runs through the pots and out the drainage hole the plants are considered watered. And it is easy to assume that as the water runs through the pots the soil must be saturated.

But this is rarely the case. The fact is that the water runs through too fast and the soil does not have enough time to fully absorb what it can hold.

This is also why we may need to top water our pots several times and empty the excess after each watering. And this is one of the main reasons why bottom watering is a superior method.

Bottom watering allows the plant to soak up water at its own pace. And depending on the quality of the potting mix and the size of the pots, the time needed can range from a few to well above ten minutes.

Always bottom water seeds and seedlings

There are of course exceptions to the rule but generally speaking established plants let us know when we are not watering them enough.

Plants get that limp look, leaves start to turn yellow and the plant starts to lose its overall vigour. But most of the time the plants forgive us and spring back when we give them water.

But what about young delicate seedlings or seeds about to germinate? That is another story. Seedlings and seeds are very sensitive to dry outs as well as overwatering. 

The seeds need the moisture level to be constant to germinate and sprout. You will not see any growth from seeds if the top of the soil is dry.

First leaves from bottom watered oregano seeds
Bottom watering oregano seeds

Seedlings are also very sensitive as they develop. They have no reserves and need water to grow strong roots and get established.

It is important to find that correct level of watering where we give the plant enough water to grow and thrive but not to risk waterlogging the root system.

We want the soil to stay moist but not wet. And if the soil feels dry we need to water.

But if we are watering pots too much we risk root rot and other problems as the plants roots are sat in constant wet.

You need to find a balance. You need to get it just right.

And the best method I have found to accomplish this is to always use bottom watering for seeds and seedlings.

Bottom watering starter pots with drainage holes

Soil changes color as it absorbs enough water
Top of the soil turns dark as it absorbs water

It is quite simple to water pots from the bottom. At least starter pots and smaller pots.

You simply fill a container with 3 centimeters (just over an inch) of water and place the pots in the bath.

The soil will absorb the water through the drain holes.

When the soil’s surface turns dark in color and you can “see the wet”, you simply remove the pots.

Place them on a surface to allow any excess to run off through the drain holes and then place them back on their drainage plate or saucer.

It is really that simple.

Pros & Cons Bottom watering established plants

Just to be clear. I recommend bottom watering all seeds and seedlings without exception.

But where established plants are concerned it is a bit more tricky. Here are 4 factors to take into account when bottom watering established plants.

Hard work bottom watering large pots

You could of course water all pots with drain holes from the bottom. But it is not very practical with larger sized pots. 

It is easy and convenient to bottom water small to medium sized plants and pots.

You should however not feel a need to water 20 gallon containers with tomato plants from the bottom. It will be hard work and it will also take a long time for the soil to absorb enough moisture.

Bottom watering leads to salt buildups

Should you decide to use bottom watering for all your pots you should at least once every two weeks or so alternate and water your plants from the top.

Watering plants from the bottom will lead to a build-up of salt in the soil over time. This is also true when you water pots on saucers from the top. This is however not an issue for seeds or seedlings during the short time they need to develop.

The trick to manage salt levels in your potting mix is to every now and then use top watering to let the excess drain out of the drainage hole in the bottom of the pot. You simply flush the salt build-ups from your soil.

For mature and established plants it is important to not only bottom water the plants. You should alternate between the two methods.

Watering root bound plants from the bottom

Plants that are root bound are unable to soak up water effectively when watered from the bottom.

Needless to say these plants need to be re-potted as they are “all roots”.

It is however easy to miss that a plant needs to be re-potted when bottom watering as pots often gets the same amount of time to soak up the water.

bottom watering plants with hard and compact soil

Compact soil will not absorb water effectively. Your plant will sit in the water and when you remove it you will see a water run off from the drainage holes.

But it will only be the very bottom of the plant that has absorbed water leaving the rest dry.

Bottom watering in our herb gardens

As far as I am concerned there are no real disadvantages to bottom watering.

As you have already read there are things to be aware of, but I do believe the advantages far outweigh the potential risks.

And when we are dealing with seeds or seedling in starter pots, where we need to be extra careful, it is actually easier and bottom watering does save you time.

Simply place all your small to medium sized plants in a tray with an upright edge and simply add water. Now the pots will absorb water and you can remove the pots as they have had enough water.

But as soon as the seedlings turn into young plants I start watering using a watering can with a rose.

Why?

It is simply a matter of convenience. It is hard work to place larger pots in water baths. I also use a moisture meter that helps me check the water level and moisture when I am unsure.

Soil moisture meter helps check soil
Soil meter help to check when it is time to water plants

And it takes a lot longer for the soil of the larger pots to absorb enough water to turn color and be ready. 

I do however have some larger pots that I water from the bottom. Mainly because the plant spreads to cover the entire area of the pots (thyme) or prefers to dry out between watering and then to be watered thoroughly (oregano).

But I have to admit that I rarely use the bottom watering method for pots larger than 15 centimeters (6 inches) in diameter.

Frequently asked questions

Meet the author: Mattias is an experienced gardener spending most of his free time on his knees among herbs, plants and garden vegetables. For the past two years he has been sharing gardening projects and how-to tutorials on the NordicLavender website and YouTube channel.