10 Steps to intensify your garden
1. Tall trees and the three tier system
Basically this involves planting trees, pruning off their lower branches so light can get underneath, then planting shrubs and perennials and then ground covers below that... and letting animals, domesticated and otherwise, rummage through the lot.
As I look out the window, for example, I can see an elderberry with its lower branches pruned off, so it's quite light below it. Roses, sage, daisies, berries and grevilleas are planted on three sides of it; on the fourth are impatiens, pansies, florence fennel, foxgloves and the odd strawberry. (We get a few of the elderberries, and a lot of the flowers- they make an excellent hayfever preventive and I use them for their natural yeast too, but we don't get any of that lot of strawberries. The wombats love them too much.)
Chooks, ducks, and the other wild animals forage through the lot- and a space about two metres square probably provides more food than many small gardens. See also 'shady bits' below.
2. Trellises and posts
You may only have a handkerchief sized garden - but if you grow upwards instead of outwards you may find an acre or so. Angle trellises so they catch the morning sun; grow climbers up posts and other forms of support. See diagrams. You can buy climbing forms of tomato, beans, peas, pumpkin, rock melons, watermelon, cucumbers etc
We also grow hops, grapes, hardenbergia, clematis etc UP other trees- graopes peering out of lemon trees, hops tangling through limes, chokoes in the oranges, kiwi fruit up the chestnut. this saves space...but it also means that you help disguise the plants so that pests don't attack them. (Our hop laden limes are always the last to be attacked by stink bugs, and most times they miss out altogether.) And birds, possums et al love nesting in vine laden trees - though they may not forage under the tangle to eat the fruit.
3. Bits on the side
Most houses have these bits - shady sections that are neglected except for maybe a rubbish bin and a leaning bike. Fill them up instead with shade loving edibles or herbs. Remember that the hotter your climate, the more shade the plants below will tolerate. In cold climates this means light dappled shade under high pruned deciduous trees. In tropical climates the shade can be quite dense and you'll still get a crop. Apart from this vague instruction, you'll have to experiment to see what amount of shade plants in your particular area can cope with.
Some Shade-Tolerant Edibles: Alpine strawberry; bamboo - some species are shade-tolerant but beware as they may become weed; blueberry varieties like Everbearer, Knoxfield Barbara, Fairview, Knoxfield Fiona; avocado - will grow in semi-shade, in fact needs semi-shade to establish, but fruits only with at least some light, establish at the dark side of the house and it'll fruit when it reaches the roof; bilberry - will fruit in semi-shade; cape gooseberry - will fruit in quite deep shade in temperate areas or in cool areas next to a warm wall; Chilean wineberry - like a raspberry with yellow berries, very hardy, fruits in temperate areas in medium shade; Chilacayote melon - will ramble up and down trees, grows in shade but needs sunlight to flower and fruit; feijoa - shade tolerant but won't fruit without some hours of direct sunlight (and often a pollinator too); hops - will twine happily through trees; Monstera deliciosa - frost free areas only; strawberries - hot to temperate areas only and they won't crop as well; rhubarb, grows tall and succulent in semi-shade, especially in hot areas; chives (Allium spp), garlic chives (Allium tuberosum); elder (Sambucus nigra); fennel (Foeniculum vulgare); garlic (Allium spp) will grow in the semi-shade under trees in temperate to hot areas, but may not flower; American ginseng (Panax quinquefolius); horseradish (Armoracia rusticana); parsley, curled parsley (Petroselinum crispum) - Common parsley will accept semi-shade in temperate to hot areas, Japanese or Perennial parsley (Cryptoaenia japonica) will also grow in semi-shade in temperate to hot areas or in a pot in cool areas on warm paving or patio; salad burnet (Poterium sanguisorba); Sorrel (Rumex spp); watercress (Nasturtium officinale); artichokes - Jerusalem (semi-shade under decidous trees); asparagus (semi-shade); celery (in temperate to hot areas); leeks (hot summers only - good under deciduous trees); lettuce (hot summers only); mizuma (Japanese salad green or green veg); potato (hot summers in dappled light under trees or pergolas); silverbeet (dappled light in hot areas, ornamental chard and other chard varieties are more shade-tolerant than the common Fordhook Giant; spinach - English (dappled light in hot areas). See aslo 'Plants That Never Say Die', Jackie French, Lothian Books.
4. Plant your eaves
Fill up eaves with hanging baskets - not in straight line but at lots of levels so you can fit more in, and they look better. There are masses of edibles you can grow in hanging baskets- see Gardens For Everyone.
5. Make use of fences
One fence can provide pumpkins for six families or enough melons for a glutton to gorge on all year. Plant them out with passionfruit- either banana or black or grenadilla, perennial beans, hops, grapes, kiwi fruit, bramble berries like loganberries or marionberries. See Trellises, posts and walls.
6. Don't use your grass like a carpet
Gardens don't have to be wall to wall grass. If you want flat stuff around your house plant strawberries instead, with paving stones in between, or prostrate thymes (There are several- not clumping thymes but small elafed very flat creepers), prostrate pennyroyal, Corsican mint, Treneague chamomile(the only flat one), woodrufff in shady spots, or kangaroo grass for seeds for the birds. Don't worry about 'summer grass' and other seed bearing short weeds either- birds love the seeds- and after all, a quick mow will tidy the place up if Aunt Gladys is coming to visit.
7. More garden beds
If you don't use a bit of grass, plant it out to garden beds, preferably perennials and useful low maintenance ones, or masses of shrubs.
8. Cover walls
Don't forget your walls either - clothe them in edibles like grapes, kiwi fruit, passionfruit - both black and cold tolerant banana - hops, perennial beans (runner beans or tropical Dolichus lab lab), as well as a host of ornamentals that birds, possums et al love to nest and clamber in.
9. Plant more thickly
A lot of planting advice is still based on northern hemisphere cold climate planting, where you need lots of space and bare ground around plants so they grow well.
Unless you live in a very cold area, plant so that your tomatoes et al mingle together. They'll grow faster in their moister CO2 rich environment, even in cold climates you can plant close together once the soil has warmed up - the mass of plants will insulate the soil so it cools less on cold nights.
Closely planted veg need less watering because they form growing mulch, less weeding because weeds can't get a toe hold. They are a wonderful cover for lizards, frogs and ground dwellers and you get more veg and flowers too. Of course you may have to tread on the odd tomato or bean plant to do your picking - but then you're getting more than enough there is extra to compensate.
10. Plant flowers and veg together
Flowers and veg to do better together ... for reasons I won't go into here but you can probably work out once you start thinking about it. It's another variant of close planting - getting more from the same space with greater pest and disease control and more wildlife into the bargain.