Filling large wooden planters

OxfordColour

Hello All, 

This is my first post so please be gentle!

I've recently purchased 5 large wooden troughs  / planters that will be creating an "exotic" patio section of our garden. 

The planters are 200cm x 50cm x 60cm and i'm trying to find a solution to not having to fill them full with soil / compost as it will be expensive and also make the planters very heavy.

I've read many things but at the moment i'm siding to using some crocks and old plastic plant pots and then adding on top a mix of soil / compost for half / two thirds? 

I am planning on keeping the plants in there for a long time so trying to get reassurance that this is a good idea.

Thanks in advance. 

Fire

Welcome Ryan. Could you let us know which plants you are planning to put in the troughs? Thanks

OxfordColour

Hi Firefly,

Thanks for your quick response.

I have a mixture of plants i'll be planting in different arrangements including..

* Cordylines (pink Passion)
* Dryopteris wallichiana ( Alpine woodfern)
* Fatsia japonica Spiders Web 
* Miscanthus sinensis Strictus
* Acanthus Mollis

In the last planter we're planning on having 2 Passiflora plants climbing along the back.

Thanks,
Ryan

Obelixx

Before you do anything I suggest you brush the wood all over with some oil to help repel water.  Cheap cooking olive oil or rapeseed oil will do.  Not virgin and not linseed which is sticky.   Line the insides with black plastic form bin bags or compost bags and staple it in place.  This helps stop the dampness seeping in from the compost.

Rather than old plant pots which can be lumpy, try and get some packing beads - expanded polystyrene - as they are light, allow for drainage and prevent compost leaking out the bottom.    Your plants sound permanent so don't put too deep a layer in and don't skimp on compost quantities and quality as they need a good home for their roots for long performance.  I suggest a mix of John Innes no 3 with 20 to 30% multi purpose for water-retention.

Any compost only has nutrients for up to 90 days so be prepared to feed with a slow release fertiliser every spring and give liquid feeds during the growing season.  Find an attractive mulch layer to retain moisture and stop compost splashing up onto your plants and also deter cats and wild critters from digging in there - gravel, expanded clay pellets, slate chips, pebbles............

OxfordColour

Thank you Obelixx for your reply..

My job this week is to paint the planters with an outdoor paint and i've also got some membrane to staple to the inside of the planters.

Regarding the packing beads / peanuts do these not bio-degrade over time and disappear? 

Thanks for the advice re the compost mix, that's good to know and also the fertilizer. I had been thinking about the feeding them rather than having to keep changing the soil every year.

Fire

I would think about black plastic liner instead of membrane as it will make for less watering. You can get old compost bags and turn them inside out. You make some slits in the bottom. It works very well. I used membrane for several large planters and now wish I hadn't.

madpenguin

I save all my polystyrene bits and bobs and use those to take up some of the volume.

Fire

Polystyrene etc does not biodegrade.

OxfordColour

Thank you - Looks like i'm digging out old polystyrene from the garage this weekend! I'll post a picture once I've finished! 

Obelixx

Beware of painting them.  It tends to degrade and need re-doing which is a job and a half and yes, plastic liner for the inside walls, not porous membrane.

OxfordColour

Thanks Obelixx - No going back now! The planters have been made out of gravel boards so i'll be painting them with Cuprinol ducks back fence paint which is supposed to be long lasting (fingers crossed).. I'll pick up some plastic liner this weekend. Thank you again