There are three things you can do to help the Lamium spread, which it will rapidly:

1. Fertilize every two weeks with a liquid like Miracle Gro, if the bed is large, using a hose end sprayer.

2. Control for slugs, because they love Lamium and will eat major holes in it when the weather is warm and damp.

3. Do not let the plants dry out. Lamium will get brown edges on the leaves which is a sign of drought and they will stop growing.

I started with 4 plants two years ago and I now have 100 square feet of Lamium.