Metal raised bed on concrete, drainage required ?

We are now trying raised beds for flower planting, too many pots so little time last year. Question is, as they are basically 1.2m x 0.6m 30cm high metal sitting on uneven concrete will I need broken terracotta in the bottom ?

They are 120L capacity so loads of soil, planting with Dahlias and Bee Blossom mainly. I am guessing water would drain freely through gaps at the base but would extra drainage help. In France and weather is becoming variable, last year all plants struggled with no rain for over 12 weeks, sun but not hot for long.
Killed a few dahlias by over watering (we are useless gardeners) hence the defensive raised beds, spread your mistakes.

Just trying to make sure we do better this year, no problem watering but very wet at the moment will that build up ?

 

You will need drainage in the bottom so that the water can drain out.

Gardening is learning from the mistakes, like everything else.

 

Trying to picture the container....you say it has 'gaps' in the bottom ..if so depending on their size and quantity then maybe OK but I would still add crocs at the bottom too. I would be more concerned if it was sitting directly on the concrete., It would definitely need to be raised a bit off the ground on bricks or those little 'feet ' that you can buy. Otherwise any drainage that the container may have will be blocked by the concrete it's sitting on.

A link would be good.

 

These are the ones, this is on gravel which is removed so free draining into the soil below.
The others are on concrete but not a tight seal, I assume some gaps would allow water out, like plantpot with broken bits in the bottom.
Probably ok without and just soil straight onto the concrete.

 

Staining not a problem as covered by a layer of gravel about 5-8cm thick. Better it runs away I guess as if sealed it would become a bog on wet days, soil will be about 25cm deep

 

Just a thought, but what size of Dahlia are you growing, I dont think you will have enough space for the really big ones, the shorter border types should be OK I would have thought.

Dahlias are very thirsty and hungry plants in general.

In winter you could have a drainage problem agreed, but I think watering will be your biggest job come summer.

 

Some large some small Dahlias, in these containers it will be 2-3 dahlias + other plants. I can water ok as we have a cistern (about 4 cubic metres) close by.
As I said we are the 'anti gardeners' when it comes to plants, we lose a lot due to lack of knowledge and general inattention. Trying to rectify that as with time on my hands now, all general building work etc done, we are determined to do things better.

I will start another post on plants we are considering.