The best way to lighten soil in established raised bed
Root vegetables do not grow well in my raised beds which are 50% topsoil and 50% compost with 2-3" compost added every year. I want to grow carrots and beets. There is not excess nitrogen. I want to lighten the soil. Is it best to use coarse sand or vermiculite? If coarse sand, must it be washed sand to avoid excess salt? How much sand or vermiculite do I need for 72 cu ft bed? Does the amendment have to be mixed into the full 18" depth or just near the surface? If just near the surface, how deeply?
It would be fine to experiment with coarse builder's sand or sharp sand. No need to wash it. Start with a 3-inch layer and try to incorporate it into the top 12 inches of soil. Let us know if this improves your root crop production. Be sure to thin seedlings to the recommended spacing to achieve best results.