Soil Calculation for Planters - seems too much?

Hi

I've got 2 new planters, and each has dimensions of 121 cm long, 51 cm wide, and 21 cm deep. Using an online calculator, it said I need 119 litres per planter. Another calculator said I needed 25kg per planter. A third one said 130 litres per planter

I'm pretty confused..........

 

Hi, sorry I can't help you as I don't calculate it, just fill pots and containers until I'm happy with how they look.

 

I worked it out as 130 litres which would fill one to the top so a bit less would be needed.
Some sellers use Litres, others use kilograms. Easier I think to work in volume rather than mass.

 

I think it would be best to buy a couple of bags and see how far it goes.
It's not going to be any exact science because compost needs to be open and broken down when you take it out the bag, kind of fluffed up, if you get my meaning.
It then gets packed down over time.

 

The third one is correct, but as pointed out, that amount would fill the planter to the rim.

 

I have to do these types of calculations every year since we use a lot of containers in our community garden.

1 cubic meter = 1000 litres

Converting the measurements into meters:

L = 1.21m, W = 0.51m, D = 0.21m

Volume of compost required:

V = L x W x D

V = 1.21 x 0.51 x 0.21 = 0.129591 cubic meters

V = 0.129591 x 1000 = 129.591 Litres


I know that B&Q's Verve 125L Multi-purpose compost weighs somewhere between 45-49kg depending on moisture content.

Lets assume 45kg per 125L bag.

That's 45/125 = 0.36kg per Litre

So, 129.591L would weigh 129.591 x 0.36 = 46.65276kg


The thing about compost is that it will get compressed and the level will drop noticibly over time so it is always better to buy atleast a third more than you actually need:

129.591/3 = 43.197L


But, don't overlook the potential free compost at this time of the year: I am talking about fallen leaves and autumn prunings from clearing the garden. Collect them all up and make your own compost.

 

The B&Q 125l bag of multipurpose compost is extremely heavy.

G.