Time is the arbiter of what works in a garden and what doesn't. It's why anything new requires at least a decade to discover its weaknesses. The great raised bed failure is right around the corner as the older wood products and shoddy construction destroy structural integrity.
Just a few winters can find your boxes collapsed from rot and bugs and moisture if you used pallet wood or untreated salvage lumber. In the throes of spring passion, we use anything we can to get a garden in the ground. Now you realize how temporary raised beds are rotting when Mother Nature has her way. Thus salvage lumber used for greater sustainability can lead to earth-to wood contact for an unsustainable application.
Beds usually become weaker all the time. When a raised bed is full of soil, plants and mulch, the contents can be surprisingly heavy. When you add water, at about 8 pounds per gallon, the cumulative weight of rain or watering stresses the joints. This places great pressure on corners and seams.
You don't want those seams to fail during the growing season, yet that's when it usually happens. It's very hard to fix in summer when full of plants, but during spring and fall, repairs and rehab can be done more easily. While planning your project, consider raising your beds if you have shallow root depth. Where soils are very difficult, the transition from one beam to two in height will ensure greater plant health, cooler roots and much greater drought resistance.
A simple five-step process helps you get your project under way on those mild winter days when the cold abates and the sun comes out. Here's how:
1. Remove existing soil if it's degraded to mostly woody matter and white perlite. Like all raised bed soils, the overall volume reduces as microbes and plants consume the fine humus. This leaves the beds chronically under-filled and marginally fertile. Stockpile excavated soil temporarily.
2. Inspect the newly exposed interior sidewalls of the bed, if they held up during the soil removal step. Use a screwdriver to stab the wood to find rotten spots. Also check the corner connections for anchorage or where they have checked or split.
3. Make repairs or replace sidewalls using recycled plastic lumber (Trex), foundation grade redwood or pressure treated beams. If the original bed was shallow, add height now.
Tip: Make repairs with wood screws and an electric screwdriver instead of nails. Screws resist loosening from expansion and contraction with the seasons.
4. Replace the old soil into the bottom of the bed, then layer quality potting soil and compost above for maximum surface fertility. It gives your seedlings a perfect place to get started in a rich environment that drives explosive growth.
5. Gently water these layers or let rain settle them over the coming months. If there's a drop, add more surface soil to bring it up to the top again. For those with drip irrigation, this is a great time to try direct burial inline drip tubing that invisibly waters your garden without ugly surface tubes and emitters.
The key to organic gardening is many of our soil and amendment additives take time to settle into the soil biology. That's why rehabilitating your beds well in advance of planting is better than throwing it all together at the last minute. It actually makes your garden more fertile overall.
Raised beds are rarely a one and done operation. They must be upgraded to keep the structure sound. Perhaps most important of all is fertility and meeting the needs of your vegetable plants throughout the season. Fail to feed your raised bed soil is like hard times when beans and cornbread are all that's in the kitchen. Like us, plants want five star accommodations, great food, a comfortable root zone and a solid bed beneath them to grow well and yield prodigiously.