In ideal conditions, a gardener may not particularly care which vegetables have shallow root systems and which have deeper ones. However, gardening conditions aren't always ideal. Some places available for growing plants may only have a foot or so of usable soil, or less, for instance. Additionally, a person may wish to grow their plants in containers that aren't especially deep. It then becomes valuable to know which vegetables can be grown in shallow shallow dirt.
What is meant by shallow
Without defining what is meant by shallow roots, there is little meaning that can be drawn by saying which vegetables have shallow roots. For the sake of clarity, shallow can be defined as being about six to eight inches deep or less. Intermediate depth would then be from eight to twelve inches deep. Deep would be more than twelve inches. Different people and agricultural groups are likely to have their own definitions of what shallow is. This also isn't exact, since shallow rooted vegetables can benefit from having deep soil to grow in and those with intermediate root systems can occasionally be grown in shallow dirt. It is simply handy to have an idea of what is being referred to.
Most leaf vegetables, meaning those that are grown primarily or entirely for their leaves, have shallow root systems. This includes such plants as lettuce, chard, kale, spinach and cabbage. The trait of growing shallowly is one reason all of these are considered to be cool-weather crops. Since the roots usually don't grow very deep, the heat of summer can cause substantial difficulties or death for these plants, because the soil temperatures can get high enough to reach to root level and cook them. This is also a reason that each of these is particularly well suited for container gardening, including window boxes, which usually aren't very deep.
It is likely that quite a few people would be surprised to learn that corn is a shallow-rooted crop. Despite the height of stalks of corn, the root system only requires about eight inches of soil. This includes both sweet corn and popcorn. The roots spread out horizontally rather than growing especially deep.
Though radishes are primarily root crops, they only need about six inches of dirt to grow in. This makes them very good for container gardening in window boxes and the like, and since they grow so fast, they can be grown for most of the summer.
Onions are marginally shallow and intermediate vegetables. A lot depends on the type of onion and how large the bulb is allowed to or intended to grow, however some varieties may grow well in nine inches of soil. Onions that produce large bulbs, such as Bermuda white onions, might need more dirt for best growth, though.
Beans are also right on the borderline between shallow and intermediate vegetables, depending on the species. Some may grow quite well with a soil depth of about seven or eight inches, while other kinds may need in excess of ten inches for healthy plants to grow and flourish.
While technically not vegetables, the roots of common culinary herbs tend to be shallow. Oregano, basil, thyme, sage and lemon grass, for instance, all normally grow shallowly. This makes them superb for growing in pots and window boxes.
There are a number of plants that are normally considered to be intermediate in root structure, which can be grown in relatively shallow soil. As a rule, though, plants with shallow roots often have greater water demands since the ground usually dries out faster. Quite a few vegetables are considered to be deep-rooted, as well. These would usually include tomatoes, peppers, eggplant and squash.
Knowing which garden vegetables have shallow roots is helpful for the gardener who wants to grow a garden in containers, or who doesn't have deep dirt to grow the plants in. This knowledge can help to increase the size of the harvest of the crops involved, too.