I have the same variety - Northern Xtra Sweet. My corn has fallen in years past...Easy to fix - in one shot! In addition to mounding some dirt, I now keep mine permanantly supported. Put a 4 or 5 ft tall stake at each end of the row, tie a strand of wire to each stake - going down each side of the row(a loop) about halfway up the overall hieghth of the stalk - make sense? You might slide the wires up as your corn grows. Also, I "pinch" the strands at a few intervals along the span w/ a twisty - this helps keep it taunt. Its simple and you only have to do this once... Besides tilling in all purpose ferts before I plant, I also use urea when the corn is 1 ft tall and once more when the tassles start to appear. One 16 oz cup of urea per 100 ft row - so about 8oz for your 4 rows (48 ft). Your corn is not tasseling early...Once you can start to see the tassles inside the plant, the stalks will grow another 2-3 ft (or more) before the tassles actually "come out". You're fine! With only 4 rows, you might need to hand pollinate your corn to help INSURE good pollination. It really is easy, but timing is everything here...Search this forum for "hand pollinating corn", but basically all you are doing here is rubbing the tassles on the silk... at the right time...

I'm thinking too little. It's really strange, some of the corn I have is growing quite fine, one is already 6 feet tall. The others are about 2-3 feet tall but they already have tassels. The six foot tall one didn't develop tassels until it was about 5 feet tall. I fertilized each one of them equally so I don't know what could be the problem

Mine is similar, and it's probably due to different emergence time of the seed. Mine had a great variety. It should pollinate fine. I actually welcome the difference because then every ear won't be mature at exactly the same time....

I'm using a raised bed, not an earthbox, but I planted 3 inches apart in 8 inch rows. So far so good, other than a raccoon that wanted a closer look at the middle! Of course so far it's an experiment based on the advice of someone here that did it in a field. Here is a link that might be useful: Sinfonian's garden adventure!