Pulling weeds and running don't mix

Yesterday, I spent 5 hours in the hot sun pulling weeds in my wife's Garden of Weeden. The temperature maxed at 100 (F) in the shade and was hotter than that in the direct sun. I also spent two hours pulling weeds in the evening when the temperature was in the mid 80s (F). When I ran this morning I could tell that I was pretty tired, so I only ran 3 miles instead of my planned 4 miles. I slept well last night, and my wakeup HR was 48 this morning (46 yesterday), but the toll on my body from hours in the sun was much greater than the benefit of the sleep. I drank a lot of water yesterday and took rest breaks, and I felt pretty good during the evening. But, I could tell almost immediately when I started running that I was tired.