Lichens are a type of colorful fungi that grow on rocks, trees, walls and paving stones. They are not parasitical, but instead feed on air, dust and ambient moisture. The appearance of lichens gives gardens an aged, mysterious beauty so some gardeners try to encourage lichen growth. It can take lichens several years to develop, but with the right environment in your garden you can create a mini-ecosystem that supports good lichen growth.
Choose a location where lichens will thrive. They need sunlight, but not too much of it, so lichens prefer shady or partially sunny places. They also do better on rough surfaces, and on surfaces that retain moisture for a long time. Wood, bricks, or porous rocks are all good places for lichens.
Start your lichens on a dry day with no rain predicted in the near future. Rain will wash off the lichen-growing solution. If the summers are very hot and dry in your area, start the lichens during a cooler part of the year.
Mix a 50/50 solution of yogurt and water in a spray bottle. Wet the entire area where you want the lichens to grow.
Dip a paintbrush into a bottle of undiluted liquid seaweed fertilizer, and paint it over the yogurt and water solution. You can cover the area entirely or just daub the fertilizer randomly over the surface.
Watch the surface for about a month. It should start to darken and look slightly mildewed. If this doesn't happen, apply the yogurt water and seaweed fertilizer again. Keep applying it every month until the surface starts getting darker.
Wait several years for the lichens to appear. Unfortunately, there is no fast way to grow lichens. They do better in damp climates because they grow a little faster when they are wet and they go dormant when they are dry.