If you want larger plantings IN your pond, and need them to last years - and be easy to move and virtually invisible, then give this a try. I've done this for almost 20 years in our ponds - I've tried various materials, including different weed block cloth (actually works OK). I finally settled on this plastic mesh to line the pots - and it's fantastic. Water gets to the roots, roots can grow out of the mesh, and the mesh gives but won't tear.
If you don't like the look of the roots sticking out the mesh, you can trim them - but they are healthy for your pond.
Step 1: I'll Start at the End
This is what the finished product looks like. The MOST important part is the milk crate. It has to be commercial grade, and not one for $5 that's for hanging files. A good crate costs from $9-$12. These don't "snap" like the cheaper ones. The handles allow you to pick up and move the pot, even with the mesh. Yea, they're heavy.
The idea is to line the crate with something that will keep in your planting media and allow water to move into the pot. You can use anything that won't dissolve over time, rust, rot or decay. Heavy duty weed block works - you need to punch holes in it after assembly - but I prefer plastic mesh. I use one with a diamond pattern, 1/8" opening.
Step 2: Cutting the Material
Not all crates are the same size. Measure the width and height on the inside. You'll need to cut two lengths of material (mesh, weed block - whatever you decided to use. Say the crate is a 12" cube on the inside. You'll need two lengths of material 11.75" wide and 42 inches long. You need extra on the ends, so we added 6 inches. If you're using mesh or stiffer material, you need to cut a little narrower - that's why 11.75". If you're using material like weed block, you should make make it 14" wide.
Find the middle and place one length in the crate, with the middle of the material centered in the crate. Push in place - in the corners fold the material in to form a crease. If you're using stiffer material like mesh, remove the material from the crate and really bear down on the crease so it takes. Then open it up to form a 45 degree angle. Put it back in the crate. Repeat for the other length. When done, there will be mesh on all four sides and a double layer on the bottom.
There will be excess material on all four sides.
Step 3: Finishing It Up
For mesh and stiffer materials, use tie straps to hold it in place. Wrap it around the edge and down. Use tie straps as shown - around the handles and corners You don't need any on the inside. For material no straps are needed - the reason we cut it wider is so you can overlap the corners.
Cut the straps ends.
Step 4: Filling and Planting
Take the planter outside and place as close to the pond as possible. This can get heavy!
I put about three inches of large stones (1.5"-2" in diameter) in the bottom. You're going to fill the rest with pea gravel. Wash the Pea gravel first - the stuff is muddy. Add two inches of pea gravel. If you want to fertilize with Osmocote or pond tablets, add them now. Add two more inches of pea gravel. You now have a seven inch base. How you plant your plants depends on the type and depth.
So I'll digress......
Are your plants marginals, bog, deep, floaters...
For my baskets I use all of these. Take a look at the photos in this step. I have Elephant Ears in two crates. The tops of these crates are 2" above the water. For the Elephant Ears (not normally a pond plant!) I only want the base of the bulb touching the water. So I filled the crate with pea gravel, and stuck the bulb 3" - this puts the bulb 1" in the water. I then mounded up pea gravel around the bulb for support. In a couple of months the bulb's roots went down through the gravel and out the sides. I planted floaters (water Hyacinth) in the corners, burying the roots as deep as possible. They looked sad for a few weeks - but look at them now.
For marginals, or deep the basket can be submerged.
I use cinder blocks to raise the baskets. These are available in a variety of styles and sizes.
OK, back to the gravel.....
The idea is to add gravel as you're planting so you don't have to dig in the gravel. That's up to you. If the thing is too heavy to lift, you can put the crate in position *then* add the gravel and plants. I have cat tails, Hyacinth, Elephant Ears, Dwarf Umbrella Palm, Parrots Feather and more in these crates. Most are hardy and come back after the winter - even after the baskets are frozen in the ice. We move the baskets around as needed to tweak the look of the pond - much easier to move in the water. If you look at the first and last photo, you can see we moved the crate to make room for the Amazonica Lily pads.
If you like Water Hyacinth (the floater) you probably know they like to be crowded. Planting a bunch in these crates gives you "islands" of Hyacinths as they remain connected unless you break them off. You can see that in the photos. You can even plant Hosta like this (although they won't survive the winter - transplant them to the ground!)
Followup - two years later...
I'm heading into my third season with these. I've had to replace a few tie-straps, but that's it. At the end of each season I pull them from the water, let them drain, and remove the annuals. I let them totally dry out over the next few months. Come March, I dump them onto a tarp, clean the gravel and put it back in. I then replant when it'e warm enough. A few of the baskets have perennials - these I just leave in the water. I'll trim back all the green and the roots for the winter.