Answer: First of all, welcome to the wonderful world of gardening. And, congratulations on having such success in starting your new vegetable garden! You'll probably want to thin out your seedlings so each plant has enough room to grow and has some air circulation all around. Plants that are overcrowded will compete for moisture and nutrients and none of them will perform very well under those conditions. Either dig up and transplant the extras or just snip off the top of the plant with scissors and the roots will die off. Tomato plants are either determinate or indeterminate in their growth habits. This means they will either grow to about 2-3' tall and set fruit all at once or they will continue to grow all summer long (5-8' tall) and continue to flower and set fruit all summer long. The type you are growing will dictate how many plants your small garden can support. Plan on each plant taking from 1-3' in width. Remove the rest of the plants. Corn doesn't mind being crowded; onions should be given 5-6" per plant to accommodate mature size plus some space between plants; green beans will grow upwards on a trellis or stake and can be planted about 6" apart; melons will sprawl and the vines they produce will produce fruit so give them lots and lots of room to sprawl.
Your veggies will need all day sunshine and a deep watering once or twice a week, depending upon weather. If you mulch over the top of the bare soil, around the plants, you'll keep the weeds down. As for insecticide - you probably won't need any your first year. If your plants begin to show insect damage, you'll need to identify the pest and then use a specific pesticide on that plants.
Good luck with your first garden!
Q&A Library Searching Tips