My neighbor has built two great looking raised beds to grow their vegetables. They are new to the vegetable gardening scene, and I hope that I have given them some good advice, which I want to share with you. They have done an excellent job of locating the beds in full sun and close to a water source. They are built on pine wood frames, and the sides are made of corrugated tin. Also, because moles and voles are bad in our neighborhood, they lined the bottom with wire mesh. Since the two planters needed about 3 cubic yards of soil to fill them, I suggested he get mixed soil from a good landscape company.
The soil they bought was a mixture of good loamy top soil, very fine ground pine bark, and some sand. Good stuff, but as with any newly mixed soil, especially those that contain bark (and I don’t know any that you buy in bulk that is not), except for two things. One, when it gets a good rain or wet it will pack down and second, decomposition will occur. Neither of these is bad, but it is important to handle these issues. Mixed soil will compact no matter how much you fill it. Compaction means that you will end up with it 3 inches to 6 inches lower in the planter than you filled it. And because it will decompose (and so does bagged mixed soils), your plants can quickly be deficient of nitrogen because decomposition uses nitrogen in the process. So, it has to be replaced. This is especially important because the decomposition process is fastest in the first year. Once the raised planters are filled, water them well. I like to let them rest at least a week before planting. This allows the soil to compact and release any fumes associated with the mixing. When you are ready to plant, add nitrogen at planting if you are planting seedlings, and once the true leaves appear on seeds that are directly planted. One application is not enough for the whole growing season. If you are using a total organic approach, I recommend processed cow manure at planting and fish emulsion or a like organic product every several weeks throughout the growing season. If you are okay using chemical fertilizers, which I recommend especially the first year, I apply a granular product at planting (like 15-0-15 or 12-6-6), and then start on a regular schedule throughout the growing season. I would recommend liquid feeding after the initial granular application, every two to three weeks at the recommended rate on the bag. Remember, a good raised bed grows better and more productive plants in season two than they generally do their first growing season.