What happens if I plan a crop that has no chart values yet?

You fill in the planting window once, and Heirloom offers to keep your numbers so you never type them again. When the crop has no chart yet for that planting method, clicking Create opens Chart update, which asks whether to update your chart with the values you just entered.

Say yes and your next plantings of that crop start from them. Say no and the values stay on this planting only; you can fill in the chart later under Charts.

The steps are in Add a planting.