How many times do you spray the area you want to plant?  That depends on
the seed bank.  The seed bank is the phrase used to describe the grass and
To get rid of the seed bank you want to water the place periodically.  The
moisture will trigger more of the seed bank to sprout and grow.  When you
see a bunch of new weeds coming up, then spray glyphosate.   Wait a few
weeks and spray again if additional weeds have sprouted.  

Do not be dubbed into thinking the seed bank is extinguished if you see not
weeds sprouting.  If the weather has been dry there could be plenty of weed
seed still in the soil, it just has not germinated because of low soil moisture.

If your garden spot has a plenty of weeds sprouting then take all summer to
eradicate weed bank.  If possible, sometime in August, cover the plot with
black plastic, preferably after a rain.  Leave the plastic on until you plant in
late October.  

The temperature will rise dramatically under the black plastic and kill weed
seed still in the top inch of soil.  The plastic also keeps weed seed from
blowing from elsewhere and landing back on top of your soil.
Herbicide tips   page two
Should you spray glyphosate or Select Max herbicide?

If it is grass, there is no advantage of one over the other.  Select Max kills
grass and does not kill broad leafed plants.

Select Max is a wonderful tool to get rid of grass coming up in  an existing
wildflower plot.

If your plot has grass growing then spray Select Max in the spring time when
the grass is 4- 6 inches high.  That may be all you have to spray for the entire
year.  Spray again later in the season if you see some grass coming back.  
Even if you see some grass here and there, once grass is sprayed; viable seed
heads are weakened and plant growth stunted.  

With Select Max here is no chemical harm done to the prairie wildflowers.   A
common ratio to use among prairie wildflowers is point five three ounces per
gallon  (.53 oz.).  

Using Select Max is a time saver in contrast to pulling out grass by hand.
This product is available at some farm supply businesses.  Select Max is
expensive in contrast to a generic Round-Up type herbicide. three