Not all plants are created equal. Here are some tips for choosing the best specimens at the nursery. While the photos here are of small plants in six packs, these suggestions can be applied to any type or size of plant.
First impressions. Obviously we are looking for robust plants with good form.
Bigger is not always better. It is so tempting to choose the largest plant, but I tend to purchase young plants whenever possible. The longer a plant has been in the pot, the more likely it is to suffer from crowded roots and lack of nutrients. I usually look for the youngest (smallest) plants for this reason. I find that the nursery will often display the oldest (most root bound) plants toward the front while the newer arrivals are tucked toward the back or under the table.
Look at the leaves. Are there signs of disease? If there is any sign of mildew, rust, or any disease, I move on. I don't want to bring any of that into my garden, and the effected plants may not be as strong since they have been diseased already.
Small holes that were created by insects don't concern me as much, as long as the insects have left. The damage has been done and if there are no more insects or signs of eggs then I'll overlook the tiny holes.
Look at the roots. Avoid buying plants that are root bound like this one.
If the roots have grown through the bottom of the pot, the plant growth has probably been stunted, and the plant will likely suffer from transplant shock as these roots will most likely be damaged when removed from the pot. At the nursery, I often will gently push the plant out of the pot to take a look at the roots, especially if the plants are potted in the small 6 packs like this celery.
The roots were starting to become crowded,
but with a gentle touch these roots can be easily spread, so I bought them.
If left another week, those roots would have been really tangled in those small spaces, and I would have left them at the store.
These plants are at the ideal stage for transplanting. Their roots are established but not crowded.
Check their posture and stability. You want the plants to be stable in the pot, not falling over. These young plants are all growing straight and tall.
One way to check their stability is to pick up the six pack and tilt it. If the plants flop over easily, they may not be planted deep enough. Look for another six pack with more stable plants.
Check for weeds. Look to see if there are weeds growing in the pot. No one needs more weeds in their garden and some potting soil may contain unwanted seeds. If one weed is growing, more may be on their way.
Look for signs of pruning. Inspect the plant to see if it has been pruned. Heavy pruning may indicate that the plant has been in the pot a long time, or that it is unhealthy and parts have died.
A careful inspection will ensure that you select the very best specimens for your garden.