Saturday 8 April 2017

Blue Water Pipe & Netting

The question about how to construct Blue Water Pipe or MDPE Pipe hoops for netting venerable crops comes up all the time on forums and I thought I would put the information I normally supply here on my blog then I can just add a link and save keep repeating the answer and simply link here.

Here are a couple of early portable hoop frames I made up to support debris netting. My beds are all 2.4m x 1.2m or 8 x 4 feet in old money. These portable frames are 1.2x1.2m or 4ft square. The one on the right is made with 20mm dia pipe and only has a lateral tie at the crown of the arch. the one on the left is 25mm dia pipe and has a tie not only at the crown but half way down either side. This offers additional support and stops the debris netting form sagging too much when wet or covered in snow.

The height of the frame on the left is half the bed width or the radius of half a circle.

The Anti fox / bird chicken wire is 20mm and the beds are 1.2 x 2.4m

A common question is how long to cut the pipes for the hoops, in the portable hoop frames above is half the circumference of the circle where the diameter is the width of the bed or 1200mm so,

That's 3.14159 x 1200 = 3770mm divided by 2 = 1885mm you could call it 2m if you wish.

The next question is how high does the hoop have to be for different crops. Look at the back of the packs or on line to find out how tall your plants are going to grow. There is also another way of looking at it and asking the question;

How high would the frames be for different widths of debris netting?

Debris netting comes in different widths we know that a semi circle 600mm high on a 1.2m wide bed is 1885mm or nearly 2m so

Finding the leg height and overall height using a 3m wide debris net

3m - 1.885m = 1.115m
1.115m / 2 legs = 557mm leg height

Total Height 557 + 600mm = 1157mm or 1.157m

Finding the leg height and overall height using a 4m wide debris net

4m - 1.885m = 2.115m
2.115m / 2 legs = 1057mm leg height

Total Height 1057 + 600mm = 1657mm or 1.657m

I tend to push the ends of my tube 200mm into the ground so the length of tube for the hoop frame using 3m wide netting is going to be 200+557+1185+557+200 = 2699mm say 2.7m

Again for the 4m wide netting it's going to be 200+1057+1185+1057+200 = 3699mm say 3.7m long.

3m green debris netting on a bed which is 1.2 x 2.4 and the hoop is 25mm and is cut to a half circle plus two legs and 200mm either end for pushing in the ground. Some people use re-bar or bamboo pins that go inside the pipe, but to me that's just too much faffing about.

The lateral stiffeners on the top and sides help stop the mesh sagging especially when the foxes use it as a trampoline. or it gets wet, it also helps keep the hoops upright and resist wind load. 

This is the netting I use for cabbages and here it's covering onions

I was lucky enough to obtain some 2.4m long plastic trim from a window installers who were moving out of the industrial park beside the allotment because they were about to start building houses on it. I have pre drilled holes at the ends and at 800mm centres to accept a cable tie that will go around the blue water pipe. I also use the plastic trim at the bottom of the netting and galvanised tent pegs hold the netting down and stop anything getting in side the hoop frame. 

Here I have rolled the bottom of the netting up tight and put tent pegs over the netting to hold it down

This is a higher sprout netting and I've added lateral restraint at the horizontal quadrants or the springing points of the semi circle and further down between the legs to stop them spreading, there is also an off cut of blue pipe pushed in the ground and connected to the hoops to offer lateral bracing against the wind and foxes.

On this frame I have two nets joint at the crown as I didn't want to buy another roll of netting, the excess netting is either rolled up and then pegged down of held down with timber and soft bricks i.e. plastic milk bottles filled with sand.  

Other questions regarding Debris Netting and Blue MDPE Pipe are:

Q: Should I use 20mm or 25mm diameter pipe?
A: I have found that 20mm dia. pipe is fine for the small portable type hoop frames, but the larger Sprout frame has three number 25mm hoops and one 20mm hoop, it's the second one in from the right in the picture above, and is really quite floppy until I brace it between the other 25mm hoops, so I would recommend using 25mm pipe    

Q: where can I buy the blue MDPE Pipe?
A: Wicks, Toolstation, Screwfix or slightly cheaper if you order online from various places. Keep an eye out on building sites, they normally get rid of the excess pipe or pipe they have been using for temporary supplies at the end of the job. I have managed to get most of my blue pipe this way, but make sure you have a saw or cutters with you as the 25mm stuff can be a devil to roll up if you don't have a spare pair of hands and some cable ties. 

The roll in the picture above was rescued from the local rubbish tip when I went to dump some stuff

Q: Where can I get the debris netting?
A: see Working Out The Cost of Protecting The Crop

Q: How do you fix the hoops to the frame?
A: I drilled a pilot home in the pipe and screwed it on larger timber frame, I have used metal and nylon/ plastic pipe clips as well. If you do the 100x50mm timber frame you can bore/drill a hole in the top of the timber and push the pipe in the hole.

Q: I have seen different coloured pipes used on allotments what is the difference?
A: The blue pipe normally for water and is meant for underground and not uv stable - not that this matters too much when using it for hoop frames & houses.

The black pipe is uv stabilised but more expensive. Only really worth the extra cash if you care about the aesthetics

There's yellow pipe is meant for gas and again goes in the ground so is likely to not be UV stable but I don't think that it's any better than the blue and I would imagine is more costly. 

Q: How do I fix the netting to the hoops?
A: I tend to cable tie the netting using the little slots that are provided in the netting for this purpose to the lateral brace that I use at the crown of the arch between hoops this allows me to remove the tent pegs or soft bricks and roll the netting up on half of the frame and weed, then I drop it back re fix it and then do the same on the other side. 

Q: I have some green plastic (i think, or metal with a plastic coating) garden canes. I was thing about putting these in the ground and slotting the pipe on to it. How far into the ground and pipe do you think it should be to secure it?
A: I have seen people use steel reinforcing rods that will go inside the blue pipe 300 to 450mm long pushed in half way really depends on your soil. I just make a pilot hole and push the blue water pipe into the ground.  .


  1. Thanks for taking the time to write such a comprehensive set of instructions - now I need to make time to follow them!

  2. Thats been a great help, thanks

    1. You are welcome Dave glad it's helped

  3. Replies
    1. You are welcome jonnytepp glad it's helpful

  4. Thank you this was really helpful. Pictures are brilliant ❤️