October to April is prime bulb-forcing season. Amaryllis and paperwhite bulbs can be forced into bloom this time of year in your very own home. Amaryllis are beautiful, statuesque flowers with large trumpet-like blooms that come in a variety of colors. They don't need a cold spell to start them into bloom - actually freezing temperatures would kill the bulb, because they originate from tropical South America. However, I would recommend them for gifts as opposed to centerpieces, because it is hard to predict exactly when they will come into bloom. Some varieties shoot up leaves first, and some will send up blooms with leaves following a month later! Blooms often open 7-10 weeks after planting. Try www.amaryllis.com for your bulbs. Paperwhites, a fragrant cousin of the daffodil with multiple small blooms on each stem, are the most predictable and easy to force bulb. After doing a test run in your home you will see that paperwhites only take three to four weeks to bring into bloom, and the buds will open over a period of a week or two. Like the amaryllis, paperwhites don't need a cold spell to start their growth spurt. However, a common problem with paperwhites is the tendency to become lanky from too little sun light, which causes them to flop over with the weight of their blooms. This is easily remedied by watering them with a 5% alcohol solution after they show signs of root and leaf growth. Check out this study from Cornell University for more information: http://www.hort.cornell.edu/department/faculty/wmiller/bulb/Pickling_your_Paperwhites.pdf. I recommend planting paperwhite bulbs in small river rocks in a glass container, so that you can be sure that not to over-water the bulb. Be sure to keep the water filled so that it just touches the bottom of the bulb. Any higher and the bulb may rot. Place the containers next to a window and watch them grow. Try www.smithandhawken.com for paperwhite bulbs.
Bulb centerpieces only work for half of the year. For the rest of the year you can grow wheatgrass for you centerpieces. Squares of wheatgrass are chic and easily grown. Order a bag of seeds online and grow them in plastic-lined boxes or ceramic bowls from a discount store. Add a few daisies by hiding florist's water tubes in the grass and soil and you've got a beautiful spring or summer centerpiece. Try www.wheatgrasskits.com for seeds and supplies.
For a late summer or fall wedding plant ornamental cabbage, hostas, or cosmos seeds in your garden and harvest them the day of your wedding for simple but elegant vase arrangements.
When growing your own centerpieces, always conduct a test run first, so that you know how long it takes to get your plant or bloom to perfection. If all else fails run to the nearest garden store and buy a blooming plant for a centerpiece. This will save you money and give your guests something nice to take back to their homes!