What size plants should I buy?



Nursery's (me included) usually offer a variety of sizes of perennial plants.

• price range to fit different budgets
• not everyone can dig a hole for a 2 gallon plant

I recommend different sizes based on the following:

• how close is the plant to the house - more instant gratification
• how large will the neighboring plants be (if any) try to maintain size balance, and a tiny plant next to mature one could become too shaded & would lose in the fight for water & nutrients
• what time of year is it? In the spring you can get by with smaller plants as they have all season to establish themselves. Late August and beyond, I would recommended a gallon size or large as time is running out to get established before winter.
• how much care will you give the new plant? The less reliable you are for watering at least once a week, the bigger more established plants you should get. A smaller plant will have a lesser chance of survival when neglect is involved. 

Plants that are in containers can be installed in the garden/landscape ANYTIME the soil is workable. "Workable soil" would be not frozen or to muddy. So for our zone 4, that should mean anytime from April (this year) to late October. Digging and dividing needs to stop for most plants late August. The difference? A potted or containerized plant has a root system that is in tact. After removing the pot, you should gently tickle out the roots, maintaining as much of the root ball as possible. The root hairs, that bring the water to the plant, are attached to the soil particles. If you remove the soil, you temporarily cut off the plants ability to get water. So even though you water the plant, it can't 'take it up' yet. Digging and dividing plants is more extreme to the plant, as it involves separating of cutting through the root system. Obviously taking longer to recover and reestablish itself. Dividing a potted plant like a daylily, would be the same as 'diggng & dividing,' Not after August! On your late fall perennials, it is also beneficial to apply a few inches of mulch material around the base of the plant.
It helps to keep moisture more even, keeps soil temps more even and warmer longer as it acts like an insulater. Sometimes plants just need an extra week or 2 to get established.