I've heard stories of keyboardists ruining their hands with exercises, so I want to be cautious and not just follow my intuition about stretching my finger and hand muscles.
What are good, safe stretches or exercises for a novice organist who has stiff hands because of physical work?
The good news is that as an organist you don't have to worry too much about being able to play keys with different levels of force like pianists. In fact the organist at a Church I played at switched from piano to organ specifically because his Arthritis was less troublesome when playing organ.
When my hands were a bit weak as a result of a long term debilitating illness, I recovered strength and flexibility in them by a mixture of coin tricks, card tricks, and a set of squeezy balls of incrementally increasing resistance. Mileage may vary, but that did help me.
It may be worth checking your ergonomic position and posture at the keyboard, including back, shoulders, arms, and hand positions, to ensure you are playing free of unnecessary tension.
These things said however, I suspect the best advice anyone could give in the circumstances would be to urge you to consult a professional (doctor or physio) to have your hand looked at, as they could examine and see if there's an underlying problem to address, and also be able to offer advice from a medically trained perspective.
Well, the first thing you would like is not to wake up the morning after doing several hours of yard work with stiff and sore fingers and hands. The best way to minimize that is to fill up a bucket with ice from the freezer and cold water from the tap immediately after you finish the yard work and immerse your hands in the freezing cold water for 5 minutes. That will minimize inflammation and should dramatically reduce discomfort the next day. It might be worth repeating the treatment the next day but not after 48 hours after the work.
If two days after the work there is still some soreness then "hot and cold" is the best treatment. Dip hand or hands alternately into buckets of freezing cold and warm/hot water for 5 minutes a time, finishing with warm/hot. This is to promote circulation and speed healing of any minor muscle tears.
In general you shouldn't play if it hurts. That will only aggravate any minor muscle injuries you have. You should also delay any stretching until the stretches can be done pain-free.
