I love that you can grow a whole meal with beans corn and squash---protein, bread and desert. And you don't have to do anything special to store them. After all the canning and preserving I've done, it's great to grow things that can just sit on the counter all winter, ready to use.
I love that the Four Sisters (corn, beans, squash & sunflowers) can be sown direct in the ground. I gardened for two decades before I grew these plants (Alaska was too cold) and once I had a bit of warm dirt, I was enchanted by the simplicity of it--make a hole, put in a seed. Not a little, has-to-be-thinned-on-your-hands-and-knees kind of seed, but a big fat seed you could see and hold between thumb and forefinger. Then up comes a big, fast-growing, plant that shoulders aside obstacles and grows. In addition to the simplicity and fun of it, my experience has been that direct-sown plants catch up with transplants, and may have a deeper, more drought-resistant root system. But if you need time to get the garden ready for them, or need to avoid weed or pest pressure on your seedlings, transplants are a good option too. It's mostly about what you enjoy doing, what you have space for, and when you have time available to plant. If you do start them in pots, 2 or 3 weeks ahead of transplant is plenty. Their roots need room, and more than a month in the pot will stunt them.
Soil preparation for New World crops is easy. These crops were perfected by people who used a digging stick and a hoe--no tractor, no plow, not even a spade. They don't need a perfect fine powdery seedbed. What they do need is organic matter. These crops originally were grown in forest clearings, in soil created by centuries of fallen leaves--full of organic matter and fungal mycelium. (This post has more on how New World crops differ from European crops.)
Once they're growing, summer crops vary more than you might think. They all need warm weather and are killed by frost, but they like different niches. The traditional ways of growing them recognized this. The Three Sisters of North America and the Milpa agriculture further south planted these crops together. This creates different niches. Instead of everything growing spread out with direct sun from all sides, there are different degrees of dappled shade, of wind exposure, of moisture, and so on. In the cloudy wet climate of Northern Europe, getting enough sun was a problem, and plants spread out in rows without any shade was a good idea. In much of North America, our seasons are much more extreme. Unless you live in the fog belt all summer, try giving your plants some shelter from brutal sun and wind. Try letting them take care of each other.
Beans are renowned for their ability to enrich the soil. Colonies of special bacteria in their roots are able to use nitrogen from the air as a food for the plant. But as Will Bonsall has pointed out, the roots can't climb out of the soil to access that air--there has to be aeration in the soil. Compacted, hard, mineral soil doesn't have spaces for air. Organic matter provides the meeting place of soil, air, and water where roots can make optimum growth and nitrogen-fixing bacteria can thrive. In tillage systems, this is provided by tilling or spading-in compost, manure, shredded leaves, etc. In no-till systems, the tunnels made by earthworms, last year's roots, and other living things aerate the soil.
Once the beans are up and you can see all the little plants, hoe the bed well (but shallowly--the roots are near the surface) and mulch between the rows. Weed competition decreases yields appreciably. I like a thick band of straw that prevents weeds from growing back and keeps bush beans from falling over as the pods get heavy. Even pole beans are sensitive to root competition and should be well mulched. This will also help keep the soil well-aerated, both by worms and by preventing sun and water from hardening the surface.
Bean plants enjoy the same temperatures humans do. They need warm soil and temperatures above freezing, but they overheat in temperatures above 85 degrees. When it gets too hot, you can see them swivel their leaves so that the sun strikes the leaf edges rather than their top surface. In hot-summer areas, it's important to choose the right varieties (Rattlesnake is particularly known for heat-tolerance. We don't carry the famed Pacific Northwest variety Blue Lake because it doesn't bloom or make fruit over 85 degrees.) You will get better yields during hot weather if you position beans where they get afternoon shade, or else use shadecloth. The type that casts 30% shade is best in most places. This website (which I have not affiliation with at all) has a handy charts for helping to choose the type and weight of shadecloth to use. I use 30% shade and prefer the more durable woven type. You don't need fancy installation. I use bamboo stakes stuck into the ground at the corners of the bed and slanted strongly outward to counteract the weight of the cloth. A rubber band will secure the cloth to the pole.
Squash seems to love growing in a compost pile. This tells you three things: It likes a lot of nutrients. It isn't picky about how fine the soil or how "finished" the compost--it will grow in stuff that's downright chunky and stinky. And it sprouts best in warm, moist places.
When you're planting squash is the time to bury your kitchen waste, a few inches below the seeds or transplants. Then mulch well with straw, leaves, hay, or piles of weeds you just pulled. Use whatever you have that can keep the soil covered and provide a steady diet of organic matter. Vining squash can be grown up a trellis to save space, or they can be planted at the edge of the garden where they can run out over a rough, paved, or unirrigated area outside the growing beds. Do not let them grow so close to corn that they try to climb it--they'll pull the stalks down. You can let the vines run amid corn, sunflower, or amaranth stalks as long as you don't let the tendrils start trying to climb the stalks--just snip any clinging tendrils. Most summer squash has a bush habit, which is compact and saves space, but is not as vigorous or drought-resistant.
Speaking of which, you will probably see squash leaves wilt and droop a bit in hot sun. This is a water-saving measure. Rather than try to keep their big leaves turgid and flat which would take a huge amount of water and hydraulic pressure from the roots, they let them droop a bit to reduce the surface area and change their angle so they're not facing the sun directly. If the plants are truly thirsty, the soil will be dry 1" down, and the leaves won't perk up when the day cools. If the leaves look normal again once the sun is off of them, they don't need extra water. The rough, hairy surface of squash leaves and stems is another water-saving measure--it minimizes evaporation from the leaves by slowing the flow of air past the surface.
Corn is a giant grass, and needs water and fertility to fuel it's fast growth. It is traditional to give it a source of nitrogen in the furrow or hill. (A hill is just a group of seeds planted in a cluster rather than spread out in a row.) Manure, compost, alfalfa meal, fish hydrolysate, blood meal and many others have been used. However, the heirloom and open-source corns we carry are thrifty plants that were not bred for excessive inputs. Good garden soil with compost at planting time and again at tasseling should be fine in most situations. On the traditional farm or homestead, hoeing weeds out of the corn was a constant summer job. In the garden, you can often hoe once and then mulch to keep weeds down and root competition at a minimum. Another approach is to plant clover or beans as a nitrogen-fixing understory.
Corn uses sunlight in a way that's unusual in our gardens but more common in tropical plants, called C-4 photosynthesis. Plants that use C-4 photosynthesis have a different structure and chemistry that enables them to keep their pores closed during the heat of the day, minimizing water loss and enabling harvest large amounts of energy in sunny weather. This trait makes corn and sorghum extremely fast-growing and productive right through hot weather and midday sun.
In the traditional "Three Sisters" garden, corn provides a trellis and some light shade for pole beans, while the beans enrich the soil and squash shades out weeds. You can see them in the photo--no bare soil, beans growing up the taller corn; zinnias and sunflowers at the edges. Corn, in it's turn, turns direct sunlight into sugar, some of which it secretes from its roots to feed the others. To make this work, you need a tall variety of corn with stout stalks to support the weight. With the shorter varieties of corn, use bush or semi-runner beans. Many of the older heirloom "bush" beans are actually short vines, called semi-runners. They are perfect for a 5' corn plant. King City Pink Beans and many of Carol Deppe's beans are examples of the semi-runner trait. This post has more on Three Sisters gardens.
Sunflowers are unusual in that they can sprout in cold soil. So you can start them first. If you want primarily flowers, make two or three plantings, say in April, May, and June. You can also prolong bloom by cutting off the flowerheads when the petals drop. Of course if you want seed, you need to leave them to mature. In order to beat the birds to the seeds, harvest the minute the seeds are hard and loose in the head, or cover them with bags to foil seed-loving birds. Sunflowers make just as good a scaffold for pole beans as corn does. Or for a really spectacular planting, try sowing morning glories at the base of the sunflower stalks once they are about a foot tall. This post has more on sunflowers.
Tomatoes are the quintessential summer crop, so it's easy to think they can soak up all the sun there is, and just pump out more and better harvests. Certainly that's the idea behind pruning and trellising them. If you live in a cloudy climate that's absolutely true. In much of the West, however (and increasingly elsewhere) they need all their leaves to shade the fruit from sun scald. And may need additional shade during hot spells. Try watching them and the forecast. In high heat, they often drop their blossoms because they are too stressed to make fruit. You can prevent blossom drop by giving shade when the forecast is for temps over 90.
Above 90 degrees, these plants shut down. So give them a break (and give yourself more consistent harvests.) Have shade cloth handy. If you know they will need a little shade break in every afternoon, you can position them so they get it. Try planting on the east side of a corn block. They'll get that important morning sun to get them making sugars and growth, then a break when heat gets high in the afternoon. Or maybe there's a spot where trees cast some afternoon shade. Use it. Do you have a patio or porch with morning sun and a few hours of shade at midday? If you aren't sure of the best position, put one or two plants in each of your possible sites and see which works best. Mulch is even more important with tomatoes than with other crops because fluctuating soil moisture causes cracking and blossom end rot in the fruit.
Where I live (cold springs, heavy soil, bad sun scald) peppers do best in 3 to 5 gallon pots. The plant in the photo at left is in a pot with a mulch of small stones to preserve soil moisture and retain heat into the night. Plants in pots warm up fast in spring, can move to a spot with afternoon shade in hot spells, get full sun when the season cools off, and move to the greenhouse, porch, or indoors to ripen in fall.
Consider pairing peppers with bush beans, basil, or other bushy companion to give shade from the side, where the hanging peppers are vulnerable to scald. Sun from directly above seems to be more to their liking. I think they evolved down in arroyos, beside little creeks, and like to have sun straight down on their canopy but not under it. Just a guess, but that's what works for me. In traditional milpa plantings, they are in among taller plants like corn, or surrounded by beans, or under the dappled shade of tomatillos. I've seen farmers bend taller plants to cast a light shade right over their peppers. It keeps the fruits safe from scald and the plants to flowering and fruiting through hot spells.