How To Build a Bog

You need to know how to build a bog if you want to grow an entire class of plants that many gardeners ignore. Or worse, if they try to grow them, they fail miserably.

And, if you've ever seen a full-blooming stand of Iris ensata , (Japanese Iris) or Primula japonica (Japanese Primula), or even Lotus, you know why I'd want to grow these garden gems.

First Consideration and Step One

To begin with, the first thing to understand in our lessons on how to build a bog, we need a way to hold moisture in the soil.

Unfortunately, it is normally not enough to simply add peat moss to the soil in hopes it will hold enough water. These plants generally want more than that.

In our own garden pond construction, we excavate at least 18 inches of soil and put a layer of heavy plastic down. The plastic is laid at least half way up the sides of the excavation so we have a good 8 to 12 inches of water holding capacity. I don't worry about bringing the plastic right up to ground level although if your soil is quite sandy, it would be a good idea to do so.

Caution - Remove the Rocks

In discussing the techniques of how to build a bog, the garden soil is returned to the hole but all rocks and weed roots are removed while backfilling.

Rocks and plastic liners can be a problem if not handled properly - it is generally better to remove rocks from bogs.

When asked about how to build a bog, I usually reply that I never really worried about having the odd hole in the plastic liner as this is a wet garden not a swimming pool. If the water drains away, then it is really easy to turn on the sprinkler and wet it all back up again. The design for this summer's project includes putting two sprinkler heads in this garden area so that when the regular garden gets one dose of water, the wet-plant area will receive a double dose.

Hose or Nearby Tap for Summer Maintenance

Water is certainly something you want to pay particular attention to when it comes to any water garden project. You'll have to keep the area topped up with water throughout the heat of the summer. So do plan on having a tap nearby or at the very least, a long hose that will reach the garden so you can put it on trickle and leave it to soak.

This kind of garden is perfect for placement under the downspouts of eavestroughs. I do note that you'll need some form of water breaker on the downspout or you'll quickly carve a canyon trench in the peat soil.

How Large to Build Your Bog?

This bog garden can be as large or small as you desire.

My biggest to date was 6 feet wide and about 45 feet long.

Simplest and Smallest

The simplest and smallest method is simply a peat moss bale, set on edge and buried into the garden. The top was cut off the bale once it was buried to give me a tiny garden that was 2 feet long, 1 foot wide and 2 feet deep.

Soils for Bogs

Acid soils are the second thing that these wet-plants tend to like.

I've found that bog gardening in straight peat moss grows great plants and tend to be quite liberal with the peat when constructing any outdoor wet-plant garden bed. The big bed mentioned above was completely filled with peat, there was no soil added at all.

The kind of pond edge that attracts dragonflies to breed, lots of moisture and bog plants

If you're building a blog larger than a peat moss bale, this soil recipe will allow you to grow great plants. Use approximately 30 to 50% peat and the rest good topsoil or the soil from your excavation.

How To Wet the Peat

Getting all this peat wet in our project is a chore for Job. You need that kind of patience because peat is slow to wet.

Turn on the tap to a fast trickle and walk away from a large peat bed. Once it starts floating, turn off the tap and wait 24 hours. Mix it up or turn over the soil in the bed and repeat the hosing. Keep wetting down the soil until it is completely wet from top to bottom.

This process took over a week in my large garden and I mixed the soil up between each soaking.


I do add compost to the soil mix. The more the merrier. It is neutral so it does not change the acidity but it does provide all the nutrients these plants desire.

You'll find that regular chemical fertilizers with their high Nitrogen counts will overfeed and cause the peat moss to degrade too quickly.

Overfed plants look good initially but then they get floppy and weak.

Weak plants are prone to disease and insect attacks.

Also remember that most wet-area plants are quite happy being fed on the poor side, they do not need excessive amounts of fertilize to give good blooms.

The second reason I add compost and a few shovels of soil to my bog project is because I want the micro-organisms that live in acidic soils to get established and start creating a good soil ecology.

A good soil ecology will do more in the long run to create a great garden than any amount of fertilizer will ever accomplish. So, go natural on this garden folks, both your plants and your garden will thank you for it. And those are the simple ways to go about our build a bog project.

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I want to create a bog to clarify pond water  I have two koi ponds with two separate waterfalls. I am trying to minimize UV lights, bacterial agents etc that is necessary to clarify the water especially ...

how big does a lotus spread  The bog is about 2 and a half feet wide and 10 feet in length, and 3 feet in debth. How many lotus do you recomend me planting in the pond/bog to fill ...

Do bogs have a bad smell?  Hi I wanted to build this bog you are talking about but I was afraid that if it is too wet it might create a bad smell of stagnated water. I am also worried ...

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