1. Know it's Features
Most transplants will come with detail on date to maturity (when to harvest), amount of sunlight needed, spacing, and even photos of the vegetable.
"Patio" and "Bush" are two words that can denote good container varieties.
Aim for short maturity dates for melons (less than 100 days) in Northern Illinois.
2. Buy from Reputable Nursery/Greenhouse/Home and Garden Center
You will find similar varieties at many of these businesses.
Plan your visit now as some varieties may be sold out sooner than later.
3. Examine Thoroughly
If a transplant you select has whiteflies/aphids/disease spots, put it back and purchase a different plant. You do not want to introduce these to your garden.
4. Purchase with Planting Date in Mind
In Northern Illinois, May 15-June 1stis when most summer vegetable transplants can be planted; however, check the weather after your transplant date.
If temperatures are in the low of 40s F/into 30s F,plant closer to June 1st.
5. Avoid the bargain transplants
While potentially a good deal, the plant may not be able to recover when transplanted outside.
Local Foods and Small Farms Extension Educator