Soil ph

Hi.

Can anyone offer advice please. I was given a soil ph reader as a present. It has a gauge on top of a long spike.

As it was a new toy I went all around my garden and wherever I stuck it in the soil it read 7 or just under. Thinking it was not working I tried it in my newly planted tubs. Here I got a reading of 5 -6. This was new multi purpose compost. So the gauge must be working OK.

I dont have any problems growing most flowers / shrubs in my garden so should I worry that the ph is 7 all over or would I get better results trying to get the ph to around 5 -6. If you think it would what would you suggest I put on/in the soil to lower the ph.