Your piano needs to be tuned like you need to go for a jog. You don’t always do it, but you know you’d be better off if you did.
Multiple variables factor in to what can cause a piano to need servicing. Moving the piano can jostle the pins and strings; playing hard can stretch the strings where they are met by the hammers; entropy of a large wooden instrument sitting unplayed even.
In North Central Texas the greatest contributing factor to a piano falling out of tune is our weather. Texas weather can swing from hot to cold suddenly, sometimes on the same day, and with it comes minute changes in humidity that can affect all the wooden pieces of your piano.
Look at your piano – it is 80% wood, with some iron, felt and plastic (or ivory) mixed in. That means that 80% of your piano is especially vulnerable to changes in weather – temperature and humidity. The spruce soundboard in your piano expands and contracts with changes in the weather, causing your piano’s tuning to be altered – even if it hasn’t been played.
A climate controlled environment helps, as does covering the piano or keeping the lid closed when it is not in use. In the end, though, your piano goes through changes every time the weather changes and in Texas that can be frequently.
Any piano technician will recommend that you get your piano tuned with the substantial season changes – usually spring and fall; every six months. This will not only keep your piano playing at it’s best but keep your piano “trained” in tension across the strings.