There are benefits to shallow rooted specimens if you have limited space/ the quality of the soil/the root zone depth is not sufficient. Most plants by their growth habit will penetrate their roots far below the surface. Some will have lateral (branching of from main stem) and some fiborous (fine, feathery roots). These are designed to source nutrients, water and find an available space to develop. However, It can be a problem at times, if roots are close to the surface leaving them exposed, vunerable to the elements and potential harm caused by animals or other external disturbance.
The benefit is that stem cuttings can often be used as the method to propagate successfully. The plant can be transplanted without fuss and generally can be moved at the right time without any problems. These plants can be often quick to establish and straightforward in nurturing. This can be a nuisance, when the plant is too happy and can become quite invasive.
All ash have relatively shallow roots but are not keen on being moved so an exception to the rule. (Fraxinus – woodland and Sorbus – mountain). The contorted Willow, as with all willows, is very close to the surface and can be easily damaged by aggressive winds. In fact, the closer the plant roots are to the surface, it will affect what you choose to plant in that area if anything at all!
Mahonia (x media/winter sun) will give you a show of flowers from late winter to spring and as an evergreen provides attractive foliage all year round. The only pruning is to retain the shape so a thinning exercise periodically is needed. It does prefer a shaded location, but as long as the soil is moist.
Hydrangeas – by the very name, these plants need a lot of water which is why it is unfortunate they’re shallow rooted. The plant can be affected by sun scorching and often intolerant to drought conditions. Hydrangeas like sun to partial shade. The colour will depend on the Ph level of the soil. What natural aluminium resides in the soil. The more acidic the soil, the more likely the hydrangea is blue. The more alkaline the more likely the flowers are pink. Hydrangea quercifolia – the oak leafed hydrangea offers white flowers from summer right through to autumn. The attractive foliage from spring. It prefers a slightly more acidic soil.
Azaleas prefer light shade but are a contender for any border. Similar to Rhododendrons they are shallow rooted and can often be containerised to ensure the soil is suitable for them. Rhododendrons do prefer a partially shaded aspect and a little sheltered. They do have a tendency to become leggy within, so an annual prune will retain the plants vigour. This plant is acid loving and must be planted in ericaceous soil to perform well. A spring flowering shrub that provides fragrance and flowers April onwards.
Virburnum offer a number of functions. This plant will attract both beneficial insects and habitat for wildlife in the winter months. Virburnum x bodnantense is a variety that is scented too. so a productive shrub. V. tinus, as an upright bush or effective hedge offering foliage, flowers and berries offering the same benefits.
Some Climbers as Honesuckle and Jasmine do have shallow roots. The plants have a mat forming growth habit under the surface that give the plant stability. This extensive habit is very dense and highly effective. It has no need to penetrate further down.