If you are buying ready-grown annuals at a garden center or nursery, don’t buy those that are already blooming. It’s better to “buy green” because these younger plants generally survive transplanting more successfully than those in bloom. Soon, they will recover from the shock and catch up to other plants and bloom.
Bigger isn’t better. Tall, lanky transplants are usually under stress from surviving on the shelf. They may lack water or light and their plants may be pot-bound and too insubstantial to sustain the top growth that results after transplanting. Look for plants that are short and compact, with lots of side branches that can grow and stretch out. If there seems to be one main stem, pinch the tip before you plant. Zinnias, marigolds and snapdragons are some of the plants that will reward a transplant pinching with bushier growth.
Feel the soil. If it’s completely dry, the plant is probably already under stress. Transplants should have moist soil, with leafy top growth in a deep, healthy green.
Annuals are typically sold in six-packs, but they are also sold in flats, or shallow containers, with up to 24 plants. Flat-grown plants typically intermingle their roots, so be careful when you separate them. When planting, try to break as few roots as possible. Spread the roots around the hole so they can grow in all directions, and water well.