I usually ask friends and family for starts off their plants. When I go to a nursery or store that sells plants, I look on their floors. A lot of times you can find broken stems that can be rooted in water, or flower heads that can be dried for seeds to start your own plants. Check craigslist, a lot of times people want to thin out their flower/plant beds and will let you get diggings for free. Go to yard sales and just ask the people for a start off theirs, most will comply.
Since we live in a condo, our gardening is limited to potted plants. When I get a new plant, I always make at least 2, sometimes 3, pots out of it. I divide them and re-pot them with new soil. I always save old pots in my storage closet, so I don't have to spend money on new pots each time.
I love red begonias and I bought one a few weeks back which I was able to divide into 3 plants. All are flourishing, and you can't tell which pot had the original in it. This saves money and also keeps plants from becoming root bound so quickly.
I go to the home improvement centers and some have plants that have been returned or wilted a bit at 90% discount, I just picked up some hanging basket flowers with basket, and all for less then $1 each! All the need is a little TLC.
When we moved into our new house, we sent out a message on Facebook letting friends and people in our area know we were looking for flowers/plants for landscaping our yard. We had people respond with offers to share their overgrown liriope, daylilies, vinca, lamb's tongue and even blueberries. What a blessing!
Also, if you live near a farm or know people who own livestock, it's a great way to get "fertilizer".
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