If you live in a temperate region with limited summer weather, vegetables with longer growing seasons should always be priority to start indoors. Slow-maturing crops, such as pumpkins and watermelons, can take 4 full growing months or more. In addition, there are some plants, such as tomatoes, that are more susceptible to cold and need consistently warm weather to thrive. Planting them outside too early will result in frost killing them. Planting certain vegetables like this too late results in plants getting ruined by Fall frosts before the tomatoes on the vine are even ripe enough for harvest. All of your hard work can go to waste in just one night if you're not careful and don't plan accordingly.