For some reason, somehow, my garden is growing grass in it this year! Please help.
This happens. Grass clippings or grass seed make their way in. You can pull it by hand, cover it with newspaper or weed fabric, or pour boiling water on it. Be careful though, boiling water will kill anything that it comes into contact with.
What is the best agent to use to drench soil to get rid of mushrooms in a flower garden?
This article, which can also be applied to flower beds, will help with eliminatong mushrooms: https://www.gardeningknowhow.com/lawn-care/lgen/eliminate-mushrooms-in-your-lawn.htm
I have a small area that I want to make into a vegetable garden, but it's full of grass and some weeds. I've covered this area with black plastic so the grass would die. It has; so how do I remove the dead grass and weeds?
New topsoil added last August to new beds in my yard have rendered a crop of tall/thin, light beige mushrooms (with a peak cap) throughout the soil. Is there a way to eradicate them?
The following articles should be of some help to you:
https://www.gardeningknowhow.com/lawn-care/lgen/eliminate-mushrooms-in-your-lawn.htm
https://www.gardeningknowhow.com/houseplants/hpgen/getting-rid-of-mushrooms-growing-in-houseplant-soil.htm
This can also be applied to garden plants.
Many years ago, I used a contact weed killer that only killed the parts of the plant it touched. This was great for spraying weeds around azaelas or other plants, as the worst that would happen is a few leaves might get killed, but it did kill most other small weeds. It was called Contax or Contac or Contact. It doesn't appear to be made any longer. Can you recommend a replacement?
This article will help: https://www.gardeningknowhow.com/plant-problems/weeds/conventional-weed-killers.htm
Being a beginner, I didn't prepare the soil properly and now I have a ton of grass encroaching throughout the veggie garden. How can I safely get rid of it without damaging the veggie plants?
You can lay down thick layers of newspaper (or cardboard) around your plants and place a mulch on top of the newspaper. The newspaper will smother the grass and the mulch will hold it down. This also has the added bonus of helping to hold water in the soil, which is better for your plants.
We have a small garden, and there are weeds, grass and pests in it. Are there any natural ways to get rid of these things, or can you suggest something at the hardware store?
For pests, I would recommend neem oil. It is organic, effective at killing harmful bugs but will be safe for people,animals and beneficial bugs. You should be able to find this at the hardware store. Here is more info:
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
In terms of weeds and grass, the best natrual control methods are either hand weeding or hoeing or smothering. Smothering involves laying down landscaping cloth or thick layers of newspaper in between your plants and over the weeds. The newspaper or cloth can then be covered with mulch to make it look nicer, if you would like.