Raised bed vegetable gardening brings a few advantages (and disadvantages) from traditional in-ground vegetable gardening practices.
There are several advantages in that you eliminate much of the need for bending over while cultivating and/or harvesting.
The higher you build your bed, the easier it is to work and this can be a serious consideration for gardeners with special needs.
Having said the above – the higher you build your bed, the more water problems you’re going to have. The bed will dry out faster than a normal in-ground bed because the water level is above ground. Gravity sucks!
The old size – 3’x8′
And it will suck the water out of that bed surprisingly quickly.
Water management in the number one problem with raised bed vegetable gardening.
Do plan on having a soaker system or sprinkler system and evaluate the water needs of the plants closely.
Soils and The Solution
Raised beds can make it easier to work the soil and create super soils.
As you construct your bed, you can add significant amounts of peat and compost to the soils to create a “super-soil” in that bed.
I’ve always liked adding one shovel of peat and one shovel of compost to every three shovels of soil when making raised beds or double-digging. This tends to open up the soil and create a well-aerated soil for gardening.
Our newly enlarged raised bed vegetable garden approximately 12’x42′
Raised Beds Are Really Big Containers
The disadvantage of high raised bed vegetable gardening is that the soil will tend to act like a large container more than an in-ground garden.
This means that compaction can become a serious issue (use drip irrigation to lessen this problem) as well as soil quality.
The higher soil temperatures in raised beds (those sides give the sun a place to shine and heat up) will give you an earlier crop but that heat will also tend to increase the rate of organic matter decomposition.
Your compost and organic matter will not last as long in your raised bed vegetable garden as they will in a traditional garden.
In our garden of small raised beds, we had such a high soil temperature in the summer of 2012, our crops were severely reduced. The solution was to build larger raised beds (we have only two-inches of clay over bedrock on our property)>
It is a good idea to work peat moss and compost into that soil every year.
For reasons that are beyond the scope of a simple article like this, plants in containers tend to grow better when the soil is more acidic than they prefer in traditional ground systems. So adding extra peat is acceptable. (In other words, the petunia in a hanging basket grows better if the soil is more acidic. In the ground, the same petunia doesn’t like that acidity. As I said, it has to do with soil chemistry, heat and a bunch of other variables).
The Bed Level Sinks
I also note that when you add a lot of organic matter to a raised bed garden soil, it will “shrink” every year. As the organic matter is consumed by the soil microorganisms (this is a good thing that feeds and keeps your plants healthy) it disappears and the soil settles over the winter.
This is a good thing as the organic matter is doing its job. Just add more organic matter every year without fail
You’ll have to plan on feeding your plants a booster shot of nitrogen at least monthly in raised bed vegetable gardening. The extra water you’re applying to keep the soil moist is driving the nitrogen down and out of the bed. If you want your plants to continue developing, you’ll have to add more readily available nitrogen (I like fish emulsion) from the top on a regular basis.
Use fish emulsion at least once a month (better every week or second week) to really boost vegetable production
The Plants Themselves
The very good news is that if you pay attention to the variables above – you can grow any vegetable in a raised bed that you can grow in the ground. You can even intensify the planting a little (crowd them) if you pay attention to ensuring there is enough air circulation between plants.
Any system that works for you and is within your budget and design thoughts will work. I’ve used concrete blocks, rock, railroad ties, cedar planks, pine planks (didn’t last long) and pressure-treated lumber to make my raised beds over the years.
It really doesn’t matter what you use to make the bed – it is the soil you put in it and how you modify it that will make or break your raised bed vegetable gardening efforts.