Growing vegetables is work and making sure you get the best return on your investment of labor is important. For maximum harvests, make sure your soil is ideal for the type of vegetable you're growing and then treat your plants like precious objects, never letting them get too dry or stressed for any reason. Keeping them healthy and growing vigorously makes them more resistant to pests and diseases, too.
Basic Vegetable Soil
Luckily, most vegetables prefer a single type of soil, rich, moist and well-drained with a pH between 6.2 and 6.8. All soils benefit from additions of a generous amount of organic matter, such as compost or manure, but if your soil is sandy or clayey add extra. This helps clay soil to drain and hold more air and sandy soil to hold more moisture.
Do a pH test once a year and add ground limestone to raise the pH. Many vegetables refuse to grow well in acid or alkaline soils so this is an essential part of garden preparation. Large amounts of organic matter acidify the soil, so if your problem is a pH that's too high add plenty, especially peat moss, before using an acidifying agent such as sulfur to lower it.
Don't forget the air component of soil. Dig and loosen your garden every year and avoid stepping on the ground around the vegetables. Light, airy soil is every bit as beneficial for plants as fertilizer. Dig deep, too. Roots can reach down several feet and looser the soil is at that depth the more vigorous your plants will become.
Nitrogen is the element that promotes leafy growth so adding bagged, sterilized manure is especially helpful for these vegetables. Chicken manure is usually higher in nitrogen than steer manure, but check the label for fertilizer content. Be sure to adjust the pH of your soil to between 6.5 and 7.0, for spinach, a real acid soil hater. Then, fertilize and water regularly to keep the leaves lush. In hot weather, provide a bit of shade if you can.
Potatos are an exception to the rule against acid soil. They thrive in a soil with a pH between 5.8 and 6.2 and are more disease resistant than those in more neutral soils. They also enjoy having half-rotted leaves and straw mixed in before planting, the sort of coarse organic matter that would interfere with seedling emergence in other vegetables.
Other Root Vegetables
Texture is most important for carrots, parsnips, beets and other root vegetables. Remove any rocks or hard clods that might interfere with root development and be extra careful to avoid walking on the soil and compacting it. Avoid adding fresh compost or manure, since these will also interfere with root growth. A neutral pH, or at least a pH not below 6.8, is best.
Celery is a crop that needs especially constant moisture. The soil should be light, airy and well-drained, but it should have lots of water holding capacity, so some clay in the make up is beneficial. Don't use so much that it causes a handful to stick together, but enough to turn your fingers dark when you work it. Organic matter is, as always, beneficial also.