Does pressure washing a house with bleach hurt my flowers and shrubs?

Generally if the shrubs are rinsed with clear water before and after bleaching there is no damage to trees or shrubs.  Flowers will be nipped and turn brown. This generally does not kill the flower – maybe just the delicate petals.  Shrubbery is rarely affected by bleaching except for current new growth.

Should I use bleach when pressure washing a house?

Sodium hypo chlorite is the basic ingredient of bleach. It is necessary to kill mildew. When used as a ratio of 1 to 15 or 1 to 12  bleach it will kill all the mildew and algae on the house.

What are those dark stains on my asphalt roof? My roof looks like it has mildew.

Actually the dark stains on asphalt shingle of your roof is not mildew at all.   The stains are a “blue-green algae” which require a special cleaning product to remove it.  Removing the stains on your roof is generally a job left for professionals because it needs to be done from the roof using hook ladders over the peak. The chemical used is an “asphalt roof cleaner”.

This cleaner mixed with water is very effective but also slippery when stepped on. The solution is applied with either a pump up bottle or with a pressure washer at very low pressure. It is then rinsed from the crown of the roof gently down toward the gutters applying minimal pressure. Basically it’s a gentle rinse like a heavy rain. Caution should be taken not to use pressure because it may result in removing some of the grains of the asphalt shingle. This of course reduces the life of your roof. The process gives you a nearly new looking roof again.