Crop Fields
In Harvest Moon DS there are 4 types of fields you can plant on. There are 14 plantable areas scattered throughout the valley, and each falls into one of the 4 types; Slow, Normal, Fast, and Super.
Slow Growth
There are 9 fields that take longer than normal to produce crops. You
will find these near the Turtle Pond, the Circus grounds south of
Vesta's farm, and in the Main Area of the valley.
Normal Growth
Your own farm has an average crop growth. This area also includes
the 3 extra Basement greenhouses you can hire Gotz to build.
Fast Growth
Where there's water you'll find nice places to grow crops. The area by
the Goddess Pond and the Excavation site will decrease the plant growth
time by 1 day. These 3 fields are fairly large in size.
Super Growth
The only place you can speed up the growth of your crops is by using the
field hidden behind the Waterfall. Since this field is in a cave you will
have to water the plants even though it may be raining outside.
The growth rate for these fields will vary by 1 day. For example, if you were growing Turnips the plant would only take 3 days to mature in the Super field, 4 days in a Fast field, 5 days in your Normal farmland field, and an agonizing 6 days in a Slow area. The fields only help with the maturity rate of the crop, not the regrow rate. Planting pineapple (5 day regrowth) in the Super field is not going you yield you lots of the high-profit fruit every 3 days. What will happen is your Pineapple will mature in 19 days instead of 21, allowing you to harvest the plant one more time before the season changes. The only exception seems to be Sweet Potatoes in the Super Field, which regrows crops every day. None of the other crops have an adjusted regrowth time.
The secret Super field is only accessible after you reach the 255th floor of the 2nd Mine. After you clear the room of wild animals, a special door will appear that allows you access to a hidden's room. Inside you'll find the Legendary Sword, which you can use to break down the rocks protecting the secret Super field behind the waterfall.
To destroy the large rocks, equip the sword, stand in front of the giant rock, and press the A button. You will swing at the rock and you'll see the stone obstacle fall apart.