soil in pots - cost vs quality

One the most difficult aspects of my balcony garden is balancing cost and quality. Like any interest or passion, it's as expensive as we want to make it - and soil can be an expensive part of the set up.

Here in Malaysia, we can find some really cheap 2kg bags of soil in the supermarket for only RM2.50. It's fantastic, especially if you're filling up a very large tub. The only problem is that water retention is low, and although they have some nutrients, they run out of them quickly.

So how can we maximise our plant potential and keep costs low?

On my balcony, most of my plants have cheap soil, because it's what I can afford. However, I'm constantly having to water thirsty plants - the hibiscus and herbs such a basil are particularly thirsty. To completely replace all the soil is out of the question. So, I've replaced the top layer with a clay soil or a mulch. They both allow the water to come through, but slows down evaporation from the pot.

For new plants, I'll choose the soil according to the plant's needs.

Thirsty plants/plants that don't like dry roots:
- invest in good quality rich soil - it saves so much time walking in and out with the watering can.

Plants that don't like wet roots or don't need a lot of water (such as aloe vera)
- the cheap soil is fine. It's got good drainage and doesn't rot the roots. Just need to add fertiliser from time to time.

What soil do you like using for your pot plants?