Space saving techniques:
Purple podded peas on a trellis, growing alongside a young grape.
You may not have much horizontal ground but I bet you have a fair amount of vertical space. Grow up! Often, it is suggested that you grow bush squash or hanging pot tomatoes and if you are confined to containers, then this might be your best bet as your 'root space' is limited but if you can use large pots or you have some ground then it makes more sense to trellis your squash upwards. This is also true of beans and peas, both of which come in 'pole' varieties.
Remaining red lettuce going to seed, interplanted with red cabbage.
Interplant your vegetables: Plant short rows of quick maturing crops such as loose leaf lettuce and baby greens in between vegetables that take longer to mature such as parsnip or eggplant. The classic combo is heading lettuce and cabbage though both of these are space heavy vegetables. You can actually plant cabbage very close together, down to 10 inches, and get small, family sized heads.
Think not just of space but space through time: Spring and fall are two times of year that gardens have a lot of bare spaces so let's fill those spots. Choose frost hardy, quick growing plants such as spinach or peas. I have had success growing a row of shelling peas in the middle of where I planned on putting my potatoes. If you always have some seedlings on the go, you can fill the empty spot left over from garlic with a fall maturing kale or a even a second crop of peas.
Plant on the slant: If you have a south facing wall, you can use the hypotenuse. Create a slight slope to increase your growing space. A southern slope will also warm more quickly in the spring. Or you could be really creative and create a sloped planting surface or wall filled with pots. You could, for example, get a hay barrel, hollow it out some, fill the space with compost or aged manure, then stick some pumpkin seeds on top, the pumpkin vines would sprawl down and around the 'planter' rather than along the ground. In the meantime, plant some greens to grow out from the sides of your planter. I've never tried to do this but the idea sounds fun.
Hot peppers like their hot pots.
Plant in a pot: Convert a gardenless part of your yard such as an unused parking spot or a balcony to a grower's paradise by using large containers like child's swimming pools, or large storage containers. Make sure these containers have adequate drainage holes. You could even put an inch or so of coarse gravel on the bottom. Mulch the top afterwards to help preserve water.
Rhubarb hanging out with columbine.
Decorate with vegetables: Don't be afraid to add those edibles to your perrenial beds. A lot of edible plants are attractive and besides, you'll be saying to your neighbours that you are proud to grow some of what you eat.
Space saver vegetables
Peas - climbing varieties such as tall telephone pole
Beans - pole beans, many varieties
Summer Squash - trombocino, also matures to a butternut variety
Winter Squash - most varieties. The small fruited ones are easy to trellis
Many greens - great cache crops and season extenders
Most root crops including turnips, carrots, beets
Garlic and onions are both harvested early allowing for a fall planting to follow
What's your favourite space saving vegetable?