Thanks so much for reaching out with this question. Your cucumbers may not be producing as a result of the extremely hot weather we have had since mid-June--especially given the lack of rainfall. This is a fairly common problem that can occur with the weather we've had in DC this summer. Persistent heat over 90 degrees can cause cucumbers to have poor pollination, drop blossoms, and for plant/fruit growth to slow. Essentially the plant is trying to conserve as much energy as possible while under stress. 

As temperatures start to cool off a bit, you may find that your cucumber plants start to recover and begin to produce fruit. You can also help reduce stress by making sure they are adequately watered (cucumbers like a lot of water), making sure that you use some sort of mulching material at the base of plants to help retain moisture, and even using shade cloth if possible to give your plants some relief from intense sunlight. 

There is some additional information here about the ways that heatwaves can affect summer crops: https://extension.umn.edu/yard-and-garden-news/heatwave-makes-vegetables-misbehave

Please reach out if you have additional questions. 

Regular wood mulch would work well. The main thing with any mulch is that you want it thick enough and on the surface (if wood chips get too mixed into the soil, it can deplete nutrients that your plants need to thrive). 

Other optiions that can be used and can be lighter weight are mulched leaves, pine needles, and straw. With straw mulch you can run the risk of having straw that has weed seeds or that has been treated with herbicides, so you have to be sure you're using one that is meant for mulching garden beds that hasn't been treated. 

Some cooler temps and rain are on the way this week, so hopefully your cucumbers are getting some relief!