Hi David. Welcome to ATP!
I see you're from Texas, so this shouldn't break your heart. Sometimes a garden planner indicates when you plant relative to last-Spring-frost-date and first-Fall-frost date. However, there should be a warning in fine print: "assuming that your region doesn't have monsoon floods or
scorching heat at those times.
I think Dave W. said he didn't plant veggies in the summer because his part of Texas is too hot and dry at those times. If you decide to fight against your climate in order to get some particular vegetable you just love, you might try planting something in deep shade "at the right time" and keep it very well watered until the hottest part of the summer is past.
Or try to shoehorn that "summer crop" into late spring or early fall. The plant might need warm weather, but can't stand great heat. Now you have to trade off unfavorable circumstances and split the difference - maybe start them indoors with some heat, and then move them outside as soon as possible, even if "the calendars" say you're planting "too early".
Then, try to get them to grow fast and become harvestable BEFORE the hot season gets too hot, even if "the calendars" say the "right time" to harvest is a date when you could stir-fry them at noon on a rock.
There is no substitute for
local experience! Well, advice from someone else with local experience is good.
Once you know what are the main challenges in your local conditions, you can
look for varieties that resist those conditions. In most parts of Texas, I would think those are "resists drought" and "heat tolerant".
Did you enter your ZIP code when you used an online planting guide? If it's really clever, it will not only look at first and last frost dates, but also try to allow for local conditions like "blast furnace". But most of those automated advisers only look at frost dates. I think that Dave built a feature into the ATP calendars so that people could enter their own experiences, thus sharing some LOCAL EXPERIENCE as well as count-the-days-to-first-frost.
http://garden.org/apps/calenda...
(Or "Goodies" -> "Garden Planting Calendar")
For me, the tricky aspect is that I have a very cool summer. The nights are almost always very cool. Thus, even though I have enough "frost-free" days to grow tomatoes, the lack of warm nights invalidates generic advice about when to plant. On the other hand, I can plant peas and Brassicas all spring and into early summer.