The straw mulch I used at the end of summer to suppress the weeds doesn't seem to be working. Should I till it and cover with plastic? black or clear? Is there something better. Or should I add more straw. I could probably bring some cardboard home from work. Is this a healthy option?
I have to guess that weeds are poking up through your straw or if there were seeds in it, they have produced more weeds. It could be that you just needed a thicker layer of straw (see this article: Autumn mulching will protect soil and prevent spring weed infestations). No need and not recommended to till it in now, just add more straw or other mulch.
Gail Langellotto, Associate Professor of Horticulture, does not recommend cardboard as it can create habitat for rhyzomous weeds. She does not recommend plastic mulch.
Mulches help regulate soil temperature, warming soil sooner in the spring or keeping it cooler in the summer, depending on the type of mulch. Organic mulches will prevent soils from warming up as fast as bare ground, but also will stop them from getting as cold. Many plants, including those in vegetable and flower gardens, need a cool surface soil. Others, such as tomatoes and vine crops, may benefit from warmer soils.
Good advice from Barb Fick, Horticulture specialist, "Whatever you use, don't skimp on mulch, a heavy layer not only keeps weeds from growing, it also keeps the underlying soil moist, greatly reducing the amount of watering you need in the summer. If you use leaves, grass clippings or straw, you might need as much as eight to 10 inches of them, Fick said.