Perennials in Containers - Soil Depth

[Hedgerow74]

Hello all!

Hope someone can help with a query I have about growing some perennials in containers!

I have bought two planters made of decking to go alongside a fence in my garden.

They measure 1.5m long, 0.3m wide and 0.4m deep.

I've worked out the volume of these to be 0.18 cubic metres which works out at a volume of 180 litres each.

I plan to plant them up with shade loving perennials and watering shouldn't be a problem as I have a drip watering system. I was thinking something like John Innes no. 3 would be the best planting medium.

I am wondering if I can get away with putting in a layer of something or other in the bottom to save on the amount of compost needed to fill them up!

I worked out that a 10cm layer of something would save about 50ltrs per container.

Would 25-30cm of soil depth be enough for these sorts of plants or am I better off spending the extra money and giving them the full depth?

Any suggestions gratefully received!

[Martin H]

I would only put the good stuff (J I 3 is fine) in the top 50% at most. The rest I'd fill with whatever I had to hand that is vaguely soil-ish, e.g. the cheapest local "topsoil" that I could find.

What used to be my front garden is surrounded by a hollow wall of similar height to your planters, built from bricks. This got half filled with a load of free soil that had been clogging up the builders yard, then I had a cubic metre of topsoil delivered to fill the rest up. I planted it up with tough small perennials, alpines and bulbs and pop the odd bedding plant into gaps; it's done fine.

Here's a couple of close-ups:

[Hedgerow74]

Thank you very much Martin!

I shall have a hunt around for some local topsoil.

Your brick versions look really lovely! Really looking forward to getting these planted up this autumn or spring next year!

[Martin H]

Really looking forward to getting these planted up this autumn or spring next year!

If you get it done in the next month or so you can put some nice spring bulbs in among the perennials. I always think a garden can never have too many daffodils!

[Hedgerow74]

If you get it done in the next month or so you can put some nice spring bulbs in among the perennials. I always think a garden can never have too many daffodils!

Oooooh! Lovely idea, I was eyeing up some spring bulbs in the local garden centre just yesterday.

Not sure how they'll cope in pretty much full shade though!

I'm finding the topsoil seems to be a bit pricey, do you think I could get away with multi purpose compost in the bottom half of the planters or would something with a bit more body be better?

[Martin H]

The trouble with MPC is that it disappears. It compresses down tight and it decomposes. So it doesn't really work as a bottom layer.

I got a tonne bag of topsoil locally for about £60 if I remember right. A tonne is roughly a cubic meter (bit less usually), so too much for you. Maybe see if you can get a half tonne bulk bag delivered, use that to fill the containers, mix a bit of garden compost in the planting hole?

There are people on here who specialise in growing in containers, be interested to hear what they think the best option is.

[Hedgerow74]

The trouble with MPC is that it disappears. It compresses down tight and it decomposes. So it doesn't really work as a bottom layer.

Aaaaaaaaaaah! I see! Thank you.

I got a tonne bag of topsoil locally for about £60 if I remember right. A tonne is roughly a cubic meter (bit less usually), so too much for you. Maybe see if you can get a half tonne bulk bag delivered, use that to fill the containers, mix a bit of garden compost in the planting hole?

I shall have a look around and see what I can find!

There are people on here who specialise in growing in containers, be interested to hear what they think the best option is.

Is there a specific bit of the forum where I might find tips on container growing?