When you plan to create a garden, you have two options on hand; Planting the seeds or Buying the whole plants. Both have their individual gains. The benefit of planting a seed is more interesting and exploring when we care for them each day and watch them grow into a healthy plant. This method however is not very effective always as I had planted a number of seeds and never seen any trace of growth.
There is less toil when a healthy plant is purchased from a nursery and planted in the garden. But there are many unskilled workers in the nursery who totally spoil the upcoming plant by adding chemicals and fertilizers in it. The only way is to choose the best grown plant in the bunch and will share about the methods used to screen them.
Although it sounds unimportant, the looks of the plants is to be checked, and you can make it out clearly if it has undergone a healthy treatment with no diseases or pests attacking it, and how fresh it looks. The drooping stems and leaves with holes reveal that it has grown up in a inappropriate soil, attacked by harmful bugs living in it.
When you are looking at the shelves in the nursery to choose your desired plant, you should try to avoid plants that have bloomed as if they do not have flowers in them they are less injured during transplantation. However the best ones to be chosen are the ones with buds. If you are left with no option other than choosing from a flowering plant it is better that you cut all the flowers for the healthy growth of the plant in future as transplanting a plant with flowers results in its death ninety percent of the time.
The roots of the plants are to be examined well before you invest on it, and you can make out how weak they are by looking at them. Always check if there are any signs of brownness, rottenness or softness, as the roots are always to be firm and well formed with a good base that can catch the soil together. The can know whether the roots are beyond or lacking their prime, according to the root to soil ratio. If there are a number of roots with very little soil, or too much of soil with very little roots in them, it is wiser not to purchase that plant.
The nursery employee can be questioned about the abnormal growth of the plant if you find one regarding the shape of the roots or the leaves, as these are unhealthy signs of a plant they may try to convince you so better give them a chance to explain things before you jump into any conclusions as they are (mostly) masters who have been trained with plants and gardening for years.
When your decision is to take a plant from the nursery keep in mind that it has been tended by someone unfamiliar who most of the times do a good job, but it is better to have a good look yourself, and the chances of transplant shock in the plant is to be avoided (when they are unable to adjust to new circumstances leading to health problems during growth) The whole process mostly results in good yields but not always.