If it's a vacant lot, then there probably was already a building there that has been torn down, or at least the area was grazed previously in the past for development. The natural environment shouldn't be just weeds, but a diverse mix of grasses and trees, etc, as well as animal life. If you ask me, I think this spot has already been compromised. You will only improve it by adding a garden. Good luck!

I live in Philadelphia in an area of the city called Kensington. There are tons of empty lots around and instead of going through the city, lots of people have taken to GG.

In lots of circumstances, the land owners have passed, and the people who own the land generally aren't aware that they own it. OR the land is owned by the city, but they are going to make you go through a lot of crap before you can do anything to it. So instead people have decided to take over the plots and by the time the city catches on, the neighborhood is soo attached, that they will fight tooth and nail to keep the little farm area...

I wouldn't suggest putting any food plants into the soil though. I would save those for the raised beds. And a soil test would be good either way to see what fertilizers you may need for your flowers.

I would also see if there are any community development committees in you neighborhood to help you obtain any supplies you may need. Here in Kensington we have the NKCDC and they help LOTS of people obtain the land they want to grow in.

And as far as harming the habitat, it's generally much more beneficial then harmful. There is another Non Profit in Philly called Circle Venture which hosts an Urban Farm Team and they work to help locals understand farming and the importance of fresh fruits and veggies. It also has an impact on the local kids in the area too, as the odds of them ever being introduced to such a lifestyle is generally pretty slim. PLUS, you no longer have the eye-sore of an empty and trash filled lot.

I think I could go on forever about the benefits, but I'll stop here. Good luck! and Best wishes! Urban Farming is a GREAT way to help clean up urban/industrial areas.

Consider taking methods from permaculture gardening, by planting native flowering plants in the plot. This will make habitat for a slew of insects and animals.

Before planting anything edible, have the soil tested. Most state health departments will do it for you for a nominal fee (just tell them it's from your yard rather than a deserted lot).

Also, consider container gardening - safer than raised beds, because even with raised beds, the roots will grow down into the native soil.

If you find out the soil is contaminated with a specific element (such as mercury, lead, or arsenic), consider doing some bioremediation. A lot of plants will actually take up these toxins naturally (some transpire the toxins, some store it in their biomass), and if you're vested in improving a piece of land guerilla style, this would be a definite way to help out.

By nature, weeds are plants that overtake other plants, specifically natives. If you're afraid that some of the plants in the lot are rarer natives (unlikely) I would suggest doing some research and identifying the plants. If they're just weeds--prevalent plants--it's not going to ruin the environment to replace them with other plants. However, weeds usually spread their seeds really well, and if you do use the soil, you will probably be pulling those weeds out again and again. Planting some native is a great idea, specifically if they are host plants to rarer insects, animals, etc.

On the natives vs weeds question, I wouldn't worry too much about pulling out natives. The empty lot is considered a disturbed area, and whatever plants are growing there now are those that evolved to grow in disturbed soils. Unfortunately, most of the plants that prefer disturbed areas are non-natives and invasive species.

However, even if the lot was chock full of natives, this plant community only represents a snapshot in the changing life of the lot (called 'succession'). If the lot remains as it is, some species (the 'early successional' species) will be pushed out to make room for more longer-lived perennial species (the 'late successional' species). The plant community is constantly changing.

Invasive species can throw off this balance, though, and prevent the later successional species from gaining a foothold. So whether you are leaving the lot in a more naturalistic state or clearing it and planting a garden, it is important to get rid of the invasive species so they don't have an opportunity to spread.

On the issue of what to plant, native species are definitely preferred, since they have evolved for the specific environmental conditions of the area, along with other plants and animals in the community. If you're going with natives, try to get locally-sourced seed. You can find out what kinds of plants are native to your area by looking at the USDA's ecoregions maps, which include descriptions of the different ecoregions and their plant communities.

However, you can also incorporate non-native (but not invasive!) species, as long as you follow the 'Right Plant, Right Place' mantra. If the plants are suited to the specific site conditions, such as light, water requirements, etc., and there is no chance they will become invasive, feel free to use them. This is kind of a controversial issue among landscape restorationists and designers, but as long as you do your research, you should be fine.

I also agree with kmswann about using bioremediation to clean up the site. For example, sunflowers and willow coppices can remove heavy metals from the soil. There's a lot of research out there on the subject, but few successful implementations, so it can't hurt to try it. Along with or in lieu of plants, adding compost to the soil helps to immobilize the pollutants, as well as adding fertility and water-holding capacity to the soil.

I can go on and on about this (I'm a grad student in landscape architecture), but I hope this helps for now. For more info, you should check out the Lady Bird Johnson Wildflower Center, and the Sustainable Sites Initiative they've been working on along with the American Society of Landscape Architects and the US Green Building Council.

www.wildflower.org

This will end up being a lot of work, so start small. Maybe:

--One weekend clear out all the trash. Wear gloves; watch out for needles and broken glass.
--The next weekend clear and plant a small area at the front - maybe 2 feet by 10. Plan carefully what you'll want to put in there. It will be fighting against weed seeds, and vulnerable to passersby.

After that you'll have a feel for how much you can handle attacking at a time, and how much effort you can realistically put into maintaining it.

One other option for quick cleanup is to determine if any of the weeds are considered "noxious" for your area: http://www.blm.gov/weeds/FAQs/FAQs.htm If they are, it may be simple to get the city out to control them. (Of course, control might mean spraying, so YMMV.) If you have to handle them yourself, start with them, because they are going to be the most aggressive in returning. And it's another way to break the job down into chunks. "The lot may not be cleared, but darnit there's no more Giant Hogweed in there!" (BTW, giant hogweed causes nasty skin irritation. Wear protective clothing and for the love of heaven don't burn it.)

I've wondered the same thing, particularly around "seed bombs" that might contain self-seeding, non-native flowers and plants. It seems that if you remove the plants from the area, you could be removing habitat for local small animals, spiders, bugs, etc. Maybe a pollen source for bees, if the weeds flower. Ecosystems are certainly tricky to think about.

weeds are just opportunists that you don't appreciate. let them have at least a little space.

Ha! Exactly my thoughts, @toughcupcake.

Whatever you do, do not grow food there until you have the soil tested. For all you know it could be an unremediated brownfield and at best it's probably got a lot of yucky stuff in it. We unearth new debris every time we change something in our yard.

Do something for the whole neighborhood instead - plant flowers.

In Permaculture, we think more of growing soil than growing food or any particular crop. The weeds are currently helping to build what is probably a very depleted soil. Many plants we percieve as weeds, such and dandelions, have deep roots that help hold the soil and bring nutrients up from deep underground.

I'd say that if you slightly bend your focus from the goal of a garden to a goal of a lot with healthy soil, there's not much you can do wrong. You can do the work of the weeds (which will take them many seasons) in a very short time span with the smart and timely application of some compost tea and mulch.