I live in an apartment that gets very limited sunlight. I was just wondering how much sunlight is required to grow upside down veggies?
Almost all veggies need at least 6 hours of sunlight to do well. You could try supplementing with fluorescent lights, but it will still be hard. Have you looked into getting an allotment garden? Many times in urban areas, allotment gardens are offered for free or for a small cost. It would allow you to grow vegetables for yourself outside.
I live in a place which is quite hot in summer. I have lots of potted plants on my balcony. Is it a good idea to put a bed of pebbles on the pots to prevent loss of humidity for plants that are vulnerable to heat?
Yes, placing a layer of mulch on top of the soil, whether it be pebbles or wood chips, will help keep moisture in the soil. You can also place the plants on a tray filled with pebbles and water, and this will help increase the humidity around the plant.
Where I live is in an apartment, and I have no land to plant but want to. Can you give me some advice on planting in half an oil drum or barrel cut length ways?
For barrels, you will just want to make sure that there are drainage holes cut in them if you use them to grow plants in. This article will have some other tips: https://www.gardeningknowhow.com/special/urban/balcony-vegetable-garden.htm
How can I turn an aquarium into an indoor herb garden?
When growing herbs indoors in a container, the most important thing to remember is to provide a growing environment of nutrient rich soil that has good drainage yet holds moisture. Fill the tank with water to check for leaks, using epoxy sealant to fix those present. An inch of small gravel or aquarium stones in the pot bottom ensures adequate drainage. Top with another inch of charcoal chips and add a layer of peat moss followed by a layer of potting soil mix (two parts potting soil with one part perlite or coarse sand). Plant your herbs and keep the soil moist, but don’t overwater.
I live in Guadalajara, Mexico and want to start my own urban garden. I notice that much of the information posted is based on the U. S. growing calendar. How do I know when it is the right time to plant my seeds? Spring here is not the same as spring there.
this will help you get started:
I am planning a patio garden. I know window boxes need to be substantial for watering purposes, but because of the location (it is in a bar area), they need to be removable because of vandalism. What type do you suggest? Also, what type of plants? This patio has sun only till 1 p. m.
There are several different options available to you with regard to your question about window boxes. It appears you only benefit from morning sun, so a mix of herbs and some perennials that like partial shade would be a good choice. You probably want to consider using window boxes made from light weight plastic materials, that would be much easier to move even with the addition of soil and plants. Many look like wood or terra cotta. This article may be helpful to get you started.
Info on how to make a roof garden.
This article should help: https://www.gardeningknowhow.com/special/urban/creating-your-own-rooftop-garden.htm