Pergola foundation design help

Dannyboy334

I am struggling with my research to come across how to design a pergola inside a raised planter bed.

I believe the best way to protect the wooden pergola posts from dampness would be to screw a concrete shoe onto concrete foundations. I could then slip the wooden post into the metal shoe.

The issue is my metal shoe would have to be 1 metre in height to get above the soil contained in the raised planter and I am unable to find any that tall.

I have designed the legs of the pergola at 125mm x 125mm but maybe this is too thick? The top of the pergola will be 2890mm from ground level.

The main contents of the raised planter bed will be Fargesia Bamboo but I also want to train climbers up the pergola so I hope my 500mm wide planter will have enough soil to support both plants.

Many thanks

Obelixx

Have you thought about metposts?   metal spike with a "shoe" at the top into which you fix your wooden post.

Dannyboy334

Obelixx said:

Have you thought about metposts?   metal spike with a "shoe" at the top into which you fix your wooden post.

The issue with them is your still going to have most of the wooden post exposed to the soil of the planter. This will hasten the wood rot on the posts.

wild edges

The simple answer is to build the raised bed the other side of the posts or line them up so they sit on top of the planter walls. You can use hollow concrete blocks and fit the posts inside them.

Dannyboy334

wild edges said:

The simple answer is to build the raised bed the other side of the posts or line them up so they sit on top of the planter walls. You can use hollow concrete blocks and fit the posts inside them.

This will still allow plants to climb up the posts I assume? I intend to eventually have the beams with climbers growing around them.

Perki

Why don't you build the raised planter around the posts , yes more work but the post aren't in the soil . The other way is to raise the height of the foundation of the post to soil level and then use a metal shoe or set them in the concrete , you'd could use breeze block if its big enough or pour concrete into a frame work that's big enough for the post to sit on,  or just use concrete support pillars for the pergola, I wouldn't be surprised if they are plastic one support pillars available .  

 

nick615

For simple protection, start with one of the suggestions above.  Then, according to the size/shape of the timber used for the pergola, rummage through cast off plastic bottles to source those big enough to fit over it.  Remove the tops and bottoms of them so that each will overlap the one below it when placed over the timber (and whatever you choose for the bottom - see above).  A simple tack will hold them in place, and I cut the top off another bottle to produce a beaker-like vessel that will act as a cap over the upper end of each post to prevent rain ingress.  You may not like the style but.........

Dannyboy334

I will have to integrate the concrete footings into the raised planter wall. If I place them away from the wall they eat far too much space in the planter itself leaving no room for my bamboo.

I am wondering could I get away with 125mm x 125mm posts (please see my pergola dimensions), the posts in the image below are 142mm x 142mm as the shoe I found fits them. I have had to make my concrete footings 350mm x 350mm to accommodate the shoe.

I am wondering could I just use the same blockwork as the planter raised wall for the footings?

Perki

I can't see why you can't use the block work integrated with sided of the planter. As long as the bolt for the metal shoe aren't to close of the edge of the block , it will crack it otherwise . 

I did a job for someone who had a giant bamboo in a large wooden raised planter, it drove me bananas dropping leaves everywhere because it wasn't getting enough water. I were so happy to see it in a skip one day.

Dannyboy334

Perki said:

I can't see why you can't use the block work integrated with sided of the planter. As long as the bolt for the metal shoe aren't to close of the edge of the block , it will crack it otherwise . 

I did a job for someone who had a giant bamboo in a large wooden raised planter, it drove me bananas dropping leaves everywhere because it wasn't getting enough water. I were so happy to see it in a skip one day.

I think I will just use the blockwork then. From my research the foundations of the pergola posts need to be 1/4th the height of the post deep. I assume that rule would apply to my blockwork foundations.

I am cornered when you said that someone you worked for bamboo wasn't getting enough water. Do you think my planter is big enough to provide enough water for the bamboo? The soil width is only 500mm. I will only be planting the bamboo on the left hand longest side.

Butterfly66

Can’t offer any advice re construction but bamboo is a very thirsty plant and will rely on you watering if in a container. Once grown little rain will penetrate as the plant effectively acts as an umbrella. 

Few will look happy in containers over the longer term without active care - feeding, watering and every few years repotting (or if remaining in same container - lifting, dividing or root trimming and replanting in refreshed compost).

I would plant bamboos or climbers given the size of container, both together will be too much competition