Plan ahead
Make a list of what you'd really like to see in your garden and stick to it. There's no use growing winter cabbage, regardless of how lovely it looks in the frost, if no one in your family eats cabbage. A list will also keep you under control when you see the end-of-season sales and are tempted to purchase something on a whim. In addition, if you plan exactly where plants are going to go, you won't make last minute mistakes such as placing sun loving plants in the shade.
Start a compost pile
It's surprising to see how many gardeners haven't constructed their own compost pile and still pay to have their grass clippings and leaves hauled away and then, in turn, purchase fertilizers every year. Compost is free food for the garden! It helps break up heavy clay soils, absorbs water in sandy soils, and encourages microbial life, thereby decreasing that chances of any one disease becoming rampant in the garden.
Compost piles don't require anything fancy. The walls can be made of recycled 2 x 4s, chicken wire, or even hay bales. All that you need is access to the pile and enough space to turn it every now and again.
What can you put in the pile for free? Grass clippings and leaves are a great choice since you probably have your own source as well as your neighbours'. Check with local tree care companies to see if they have any wood chips to give away. Coffee grinds from the local café make excellent compost, as does shredded newspaper. Don't forget to include your vegetable scraps and egg shells. Once you get hooked on composting, you'll even start going after the local barber for hair, and even saving dryer lint!
If you're an apartment gardener or are cramped for space, a great alternative to a compost pile is a worm bin. The requirements for a successful worm bin include a good size container, usually a Rubbermaid bin, about ½ lb of red wiggler worms, shredded newspaper, and then a steady supply of kitchen scraps. The resulting "worm casts" make excellent fertilizer for garden & potted plants.
Recycle
Many of the expenditures that gardeners make for containers and equipment can be cut down by re-using items you already have at home. Margarine tubs, yogurt & cottage cheese containers and egg cartons are fantastic for seed starting. Old gardening boots, wheelbarrows, and toolboxes can make whimsical substitutes for expensive outdoor containers. Window frames can be converted into cold frames and plastic milk jugs and pop bottles can be used to make a mini greenhouses or hot caps.
Start from seed when you can
One packet of tomato seed is often equivalent to the price of one tomato start yet you get the potential of at least 30-40 plants in each packet. While it may take longer and require advance planning, starting the majority of your plants from seed can be a big savings, especially if you're using recycled containers. No need for expensive heat mats - the top of the VCR or water heater is ideal. Fluorescent tubes make a suitable substitute for expensive grow lights and can be rigged up under a table or on a shelf in the garage.
Don't forget to try to save your own seed during the season. Not only will you save on the seed purchase the following year, but you'll also be able to select seed from plants that you know did well in your climate. Most communities now arrange for seed swaps in the early spring where you can trade your excess seed for new varieties. Make sure that you save seed from non-hybrid plants.
Choose plants that keep on giving
In the vegetable garden, climbing peas, tomatoes, beans & squash tend to provide more produce than their bush equivalents. If you're limited in space, growing these plants vertically can be very successful. In addition, plants like zucchini are notorious for their yields. Trade with neighbours for food you didn't grow.
Among the flowers, try growing multi-purpose plants to get more bang for your buck. Many flowers like bachelor's buttons, violas, calendula, pansies, & roses are edible as well as beautiful. Yarrow, alyssum, fennel, cumin, & coriander all attract beneficial insects as well.
Find a friend
Not only can you share ideas with a gardening buddy, but you can also share the costs and make it cheaper for both of you. Very few of us require a whole packet of seed for the gardening season; most packets contain 40-100 seeds. Why not split the packet with a friend or else trade seed for a variety you didn't buy? A gardening buddy is also a great person to share tools with. If you've got a fantastic hoe and your friend has an excellent pitchfork, why double up?
Sharing with a gardening partner will also allow you to purchase certain inputs in bulk. If you require potting mix, why not go for the bale size instead of the small packages? Compost, if you can't make your own, is much cheaper if purchased by the yard and shared with a friend or two.
Joining a garden club is a great way to meet gardening enthusiasts if no friends or family are willing to team up with you. Most clubs also hold plant exchanges or sales where you can get plants for a real steal.