How to Refresh Raised Bed Soil

To refresh a raised bed, pull the spent crops, loosen the top few inches with a fork without turning the profile over, spread one to two inches of compost across the whole surface, work it into the top couple of inches, and top up any lost volume with a bagged raised bed mix. That is the entire routine for a bed in its second year or its tenth. You almost never need to empty a bed and start again -- the soil has not worn out, it has compacted and lost organic matter, and both of those are fixed from the top down.

A raised bed fill is mostly organic matter, and organic matter is food for soil organisms. They eat it, and the volume it occupied disappears as carbon dioxide and water. A bed filled level in March is usually two to four inches down by the following spring. That is not a fault in the fill; it is the fill doing its job.

• Decomposition. The compost fraction breaks down and the level drops. This is the big one.
• Settling and compaction. Rain and watering pack the particles closer together, especially if anyone has stood in the bed.
• Nutrient export. Every tomato you carry to the kitchen removes nutrients that came out of the bed.
• Leaching. Free drainage is what makes a raised bed work, and soluble nutrients -- nitrogen first -- move down and out with the water.

1. 1

   Clear the bed and leave the roots where sensible

   Pull annual crops and weeds. Fine roots can stay -- they rot in place and leave channels behind. Pull out anything woody or diseased.

2. 2

   Loosen, do not turn

   Push a garden fork in and rock it gently every six inches or so. The aim is to relieve compaction without inverting the layers, which would bury the biologically active surface.

3. 3

   Spread one to two inches of compost over everything

   This is the step that does most of the work. It adds organic matter, feeds the soil life, and restores most of the fertility a season of cropping removed.

4. 4

   Top up lost volume with bed mix

   If the bed is more than a couple of inches low after the compost, add a bagged raised bed mix rather than garden soil or potting soil, which are the wrong texture for a bed.

5. 5

   Add a granular feed only if the bed needs it

   A bed that gets compost every spring usually does not. Heavy feeders -- tomatoes, squash, corn, brassicas -- and any bed that cropped poorly last year are the exceptions.

6. 6

   Water it in and leave it a week before sowing

   Let the amendments settle and the soil biology wake up. Sowing straight into a freshly forked, freshly fed bed gives patchier germination.

Those figures are just the bed area multiplied by the depth in feet -- an inch is one twelfth of a foot. If your bed is an odd shape, the raised bed soil calculator does the arithmetic and converts it into bag counts.

Emptying a bed is a genuine job, so it is worth being sure. Four situations justify it, and ordinary tiredness is not one of them.

The row worth taking seriously is the soil test. Guessing at a deficiency is how beds end up with too much phosphorus; a test through a state extension service costs very little and is the only honest basis for replacing a fill. If feeding is the real question rather than refreshing, do you need to fertilize raised beds? settles it before you buy anything.

Spring is when everyone does this and spring works fine. But spreading compost in fall, after the last crop comes out, gives the whole winter for it to be worked in by worms and weather, and the bed is ready to plant the moment the soil warms. A cover crop or even a simple mulch of leaves over winter protects the surface from compaction by rain and adds more organic matter again.

Either way, the principle is the same: raised bed soil is maintained from the top, continuously, in small amounts. Beds that get that treatment improve every year rather than declining.