Raised garden beds have a lot of advantages and disadvantages. The soil that was originally in the garden was quite poor soil that we used to fill up the rice fields. This is generally 1 ½ meters deep, and turns into rock after a few days without rain. Rather than cover the whole area with good soil, which would have been quite expensive, we opted to make raised beds.
Advantages
i. Virtually no weeding!
ii. The soil stays loose as no one is walking on it.
iii. You do not have to bend over as far when you are tending the garden. On the brick beds, you also have a good seat!
iv. Less pests.
v. Control of the soil.
vi. They look great!
Disadvantages
i. Initial cost.
ii. Require a lot of watering in dry weather.
Design
The simplest of these are soil and compost mix mounded up on the original soil. These work quite well but are a temporary solution to the problem.
The second type of bed we made are from bamboo, about 1 meter from the ground. These are great for working on but because of only having around 30 cm of soil are quite prone to drying out.
We looked around for materials to make a more permanent raised form of bed with. We looked at wood and bamboo, but discounted these as in Thailand the termites would quickly eat these! Next we looked at concrete, but were warned that some of the additives from the blocks may leach into the soil, and ultimately be taken up by the plants. Finally we settled on large bricks that look rather like big lego blocks. These are great, and we even built some beds without any cement. Again, these beds need regular watering and I want to eventually add an automatic watering system to them.
Growing Medium
To fill the beds, we put organic matter into the bottom, leaves, hedge clippings and straw. We also added a few bags of cow manure in. We then filled up the beds with a growing mix of 2 parts soil, 1 part animal manure, 1 part mushroom compost and 1 part of fine coconut husk to keep the soil open.
Mulching
We found a good way to keep the moisture in was to add coconut husk as a mulch once the beds had been planted up. This also keeps down any volounteer weeds that do manage to get into the beds.