Switching off iPad

You just want to keep the battery charged to 50% for extended periods of time off. If you can check it monthly, I would do so.

This is from Apple about long term storage for iPad:

Store it half-charged when you store it long term.

If you want to store your device long term, two key factors will affect the overall health of your battery: the environmental temperature and the percentage of charge on the battery when it’s powered down for storage. Therefore, we recommend the following:

• Do not fully charge or fully discharge your device’s battery — charge it to around 50%. If you store a device when its battery is fully discharged, the battery could fall into a deep discharge state, which renders it incapable of holding a charge. Conversely, if you store it fully charged for an extended period of time, the battery may lose some capacity, leading to shorter battery life.
• Power down the device to avoid additional battery use.
• Place your device in a cool, moisture-free environment that’s less than 90° F (32° C).
• If you plan to store your device for longer than six months, charge it to 50% every six months.

Depending on how long you store your device, it may be in a low-battery state when you remove it from long-term storage. After it’s removed from storage, it may require 20 minutes of charging with the original adapter before you can use it.

Hi! I think you mean without harm? :)

There are no specific rules or guides on how long you can switch off an iPad without affecting the device. If you make sure it doesn't get dirty, wet, too hot or otherwise physically damaged while it's not being used, the only thing to worry about would be the battery.

General advice is to make sure the battery is charged to more than 50% when you switch it off for a longer period of time.

To power off an iPad --> Turn iPad on or off - Apple Support (MN)

How long are you wanting it to be powered off?

6 months is a long time. I'd personally be concerned the battery may deplete fully, which can be harmful to Lion Batteries. Is there no way the charge can be checked from time to time?