The single biggest decision you make is where the garden goes, and you make it before you plant anything. Here's how much sun vegetables need, why standing water is a dealbreaker, and how the site shapes the plan.
Photo: Ciara Ní Riain · CC BY-SA 4.0, via Wikimedia Commons.
What you need
A spot you can watch across a day to see how the sun moves over it
A look at where water stands after a hard rain
A sense of which way is south (in the northern hemisphere, the sunny side)
The most important decision in a garden is made before a single seed goes in: where it goes. A good spot forgives a hundred small mistakes; a bad one undoes good work all season. Three things decide a spot, in order of how much they matter: sun, water, and the soil underneath. Get those right and almost anything grows; get the sun wrong and nothing does.
How much sun does a vegetable garden need?
The extension services all converge on a rule of thumb of six or more hours of direct sun a day for fruiting crops like tomatoes, peppers, squash, beans and corn. Leafy crops and many herbs get by on less, four to six hours, and a few tolerate real part shade. “Full sun” on a seed packet means that six-plus-hour spot. Watch the ground across a day before you commit. The sun is lower and shadows longer than you think, and a fence or a neighbor’s tree can steal the morning or the afternoon.
The planner treats a full-sun crop in a shaded spot as a real problem:
Don't put full-sun plants where you've marked shade
If you skip this, you lose real yield. The planner warns you.
How it works: Photosynthesis. A crop whose light minimum is full sun is below that minimum in shade and underperforms. Shade you mark yourself (from a wall, fence or building the planner can't see) is separate from the shade the planner works out from taller neighboring plants.
Evidence: checked against 2 sources in the research-based literature.
Tall plants inside the bed also cast shadows on shorter ones, and where you put them decides who gets the light. The planner works this out from your latitude and each plant’s mature height, and it holds two rules so your tall crops don’t shade your short ones:
Plants over 120cm mature height belong on the north side of a bed.
This is why a bed is generally laid out with the tall crops (corn, staked tomatoes, trellised beans) on the north side in the northern hemisphere, stepping down to the short ones on the south.
Does standing water rule a spot out?
A garden wants water it can drink and drainage for the rest. The one site condition you can’t plant your way around is ground that stays wet. If water stands after a hard rain, that is a site problem to fix. Choosing different plants won’t solve it:
Ground the gardener has observed to stand water after rain is a site problem to fix before planting. Selecting plants around it does not solve it.
If you skip this, you lose real yield. The planner warns you.
How it works: Saturated soil has no air in it, so roots suffocate; and standing water lets Phytophthora release swimming zoospores, which need free water to reach a root or crown at all.
Evidence: checked against 5 sources in the research-based literature.
Almost all fruit and nut trees, as well as many ornamental trees and shrubs (including many California natives), can develop Phytophthora root or crown rot
Periods of 24 hours or more of saturated soil favor Phytophthora infections. Conversely, good soil drainage and more frequent but shorter irrigations reduce the risk of root and crown rot.
Zoospores are released from sporangia only when soil is completely saturated with water (standing water).
Remedy
You told us this ground stands water after rain. Fix the site. Changing the planting list won't solve it. Plant on a mound or berm, or build the bed up. UC IPM puts the mound at 8 to 10 inches for annuals and up to two feet, with a gradual slope, for trees and perennials; WSU asks for at least 12 inches for raspberries. Fruit trees and brambles have the most to lose, and tomatoes, peppers and eggplant are named as susceptible too. Never bury the root crown or graft union when you mound. We are not naming a drainage rate or a tile spacing, because that is an engineering number and this is a garden app.
Saturated soil has no air in it, and roots drown. Watch your prospective spot after a heavy rain. If puddles sit for hours, either pick somewhere else or lift the growing ground above the wet with a raised bed or a mound; the build a raised bed guide covers how. You also want water you can reach. A garden a long way from a hose gets watered less than it should.
What about slope and access?
A few more things tip a spot from workable to good:
Gentle slope is fine; steep is erosion. A slight grade helps cold air and water drain away. A steep one washes soil downhill, so terrace it or pick flatter ground.
Level enough to work. You’ll be standing, kneeling, and pushing a wheelbarrow here.
Near the house gets tended. The single best predictor of a garden that thrives is how often you walk past it. A bed by the back door gets noticed and watered; one at the bottom of the yard gets forgotten.
None of this needs to be perfect. Pick the sunniest, best-drained spot you can reach easily, and let the garden types guide help you choose what to hold the soil in once you know where it’s going.
Further reading
Good places to read more about the technique on this page. The grade on each card comes from that card’s own sources.
