From what I've read, it sounds like landscape mix might dry out pretty quickly, it's meant to amend clay type soils. You might want to add some regular topsoil to it. I'm no expert, so you might want to ck with the Soil, Compost and Mulch forum.

If you are using this in pots, then yes, you have made a mistake. As a general rule, you never want to use anything in pots that has the word "soil" in its name. Potting mixes are light and fluffy even after repeated waterings. This allows plant roots to move easily, to breathe, and keeps water draining to the roots don't rot. When you put soil, topsoil, soil amendments, even potting soil into pots, it will rapidly become so heavy that your plants will literally smother. Dump what you have into your flower beds. It will probably do some good there. Then replace with a good quality potting MIX.

The one exception to this rule might be homemade compost. I read all the time about the british using compost in their pots. What I don't know is if this is an english word for potting mix or if it really is compost. I have mixed my compost into potting mixes with good results in the past, but have never used it in pots "full strength".