Question
Our backyard is in major need of work, it needs to have all the weeds (chickweed, morning glory, dandelion) removed and then the ground filled (currently there is a big dip in the back yard).  The gardener we are hiring plan to spray the entire yard with an herbicide, level the yard with topsoil and sod to make areas of lawn and areas for planting flowers/vegetables.  Is spraying with herbicide safe for a future planting of vegetables and consumption.  Also, we are in the Pacific NW, is it too late to start in October to spray, and lay new sod? Thanks.

Answer
Linda,

Is spraying with herbicide safe for a future planting?

Probably, but it depends on the herbicide. Each has a characteristic residue persistence, and there's not an easy source of good information about that.  

You may want to find out what is intended to be sprayed, and read the product label.  Herbicides have elaborate legally required labelling information about their specific active chemicals. (Some available online for ex:   http://www.cwc-chemical.com/download.htm).

Since most commonly used post-emergent herbicides are absorbed by the plant through foliage, future plants aren't at risk.  Residue will be washed away or broken down before time for planting.  Spraying around existing plants, especially fruits and vegetables, would be a problem, though.

If it were my place, and I knew specifically where my veggies were going to be, I'd rely on tilling and hand weeding there.

If you are uncomfortable with the spraying being planned, do the job without it.  Tilling and adding the extra topsoil will disrupt a lot of the weeds.  Spot spraying later can take care of what will pop up.

Is it too late to start in October to spray, and lay new sod?
No, it is not too late.  

The spraying won't be as effective as it would have been in warmer weather, when weeds are actively growing, but it'll work. It also has a bigger chance of getting washed off now.

October is getting too late for seeding a new lawn, but sod just needs to keep its roots moist and in contact with soil to survive.

Hope this helps,
Mark in Portland Oregon