Answer: Sandy soils drain very quickly so you'll need to water a lot during the growing season. Or, you can amend the soil with organic matter such as compost to help hold moisture. Spread 4-5" of compost over the planting area and dig it in to a depth of about 8". Plant your flowers and then mulch over the bare soil with additional compost. This will help suppress weeds and slow evaporation. At the end of the season dig the mulch into the soil. After a few years of enriching the soil in this manner you'll have wonderful garden loam and your plants will thrive.
The lawn area should be treated the same. If it's a large area, you might consider incorporating top soil (a 3-way mix) and rototilling it into your sand. A 3-way mix contains sandy loam, peat moss and garden mulch. It will greatly improve your sandy soil.
Best wishes with your garden!
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