Posted: 08/06/2017 at 14:29
That is a very disheartening experience Mary - I'd be having a 'chat' with the suppliers of the top soil if I were you. Sounds like a load of weed infested soil to me
What have you actually done with the top soil in the garden? If you've just laid it as a layer over your existing soil then you can probably deal with this without too much bother and promptly dig weeds out as and when they appear. With luck they will just be in the top few inches of soil and a concerted effort with spade and glyphosate should see things reasonably cleared this season.
Vigilance will be your watch word to spot baby weeds coming through and zap or dig them before they have a chance to get their roots established in the soil underneath.
If you've rotavated the topsoil in your task will be more difficult but not impossible - even more important to deal with young weeds as soon as they appear and dig every last bit of them out.
Be aware that mare's tail has a waxy coating which makes using glyphosate less effective. At the very least you should bruise the stems before spraying or painting with the weedkiller. I would probably choose to dig out mare's tail. The roots can go down a very long way if it's established but (if it has come in with the top soil) it should still only be in the top 20 - 30 cms - just be sure to get all the root / rhizome out.
I wish you all the very best. It might seem disheartening now but if this a problem with the imported topsoil you can nip this in the bud if you keep on your guard.
Assuming you haven't already done so.... I would delay planting up until next year. That way you can dig and spray freely without killing treasures.