The rules

113 rules, and every one of them has to say how it works. A claim that cannot name its mechanism in a sentence is not enforced here — it is written down, graded, and left unenforced. That is the whole difference between this and a list of gardening tips. You can download the whole graded set as one file.

Spacing

How much room a plant and a bed actually need.

• A bed whose shorter side runs well past ~1.2 m has interior ground that can't be reached from its edges. Promising #
• A full-sun species must not be placed in ground the gardener has marked as shaded. Well established #
• A plant that must climb needs an assigned support strong enough to carry it. Well established #
• A plant's mature spread must fit its allocated area. Well established #
• A planted bed keeps every plant within arm's reach of a path, edge, or walkable row. Promising #
• Heat bolters that tolerate part sun, such as lettuce and spinach, are better off in the computed summer shadow of a taller neighbour than in open sun. Promising #
• Living supports have finite load capacity. Promising #
• Perennial members must not be sited in ground that is annually turned or rotated. Well established #
• Perennial woody guilds are not bed-scoped. Their ground entity is the drip-line ring. Well established #
• Plants over 120cm mature height belong on the polar side of a bed. Well established #
• Sun-requiring species must not sit in the computed shadow of a taller neighbour. Well established #
• Vining cucurbits in beds under 2m escape the bed. Well established #

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Timing

When the season lets a crop start, and the heat and cold that bound it.

• A species must reach maturity within the site's frost-free window. Well established #
• A vine assigned to a living support must be sown after the support is established — corn ~6 in (~15 cm) tall, roughly 2-3 weeks — not at the same time. Well established #
• Cold-hardy annuals can be sown or transplanted before the last spring frost — hardy crops about three weeks before, half-hardy about two weeks before. Tender crops wait for the frost itself. Promising #
• Hardiness zone is the correct variable for perennials, and only for perennials. Well established #
• Long-season warm crops are started indoors several weeks before the last frost and set out after it — tomato and tomatillo about six weeks ahead, pepper and eggplant about eight. Basil, six. Promising #
• Onion cultivar group must match site latitude. Well established #
• Pepper fruit set suffers when night temperatures stay above ~21C (70F); the same hot spell's high days compound it. Promising #
• Succession sowing at 2-3 week intervals extends harvest for short-DTM crops. Promising #
• Tender species must not be scheduled before the site's last frost date. Well established #
• Tomato fruit set fails when night temperatures persistently exceed ~21C (70F); high day temperatures (>29-32C) compound it. Well established #

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Rotation

What must not follow what, and why the ground remembers.

• A guild deposits family history across its whole footprint. Promising #
• Alliums and carrot family are unrelated to nightshades/cucurbits/brassicas and can break those families' rotation cycles — but they are not "low-pressure" and need their own rotation. A good hunch #
• Do not establish Verticillium-susceptible perennials (raspberries, strawberries, stone fruit) in ground that recently hosted Verticillium dahliae — either nightshades, or a logged planting of a Verticillium host (strawberry, raspberry or other bramble, or stone fruit). Promising #
• Do not establish Verticillium-susceptible perennials where the season log records that a Verticillium host (strawberry, raspberry or other bramble, or stone fruit) previously grew — a reservoir the coarse prior-nightshades family signal structurally misses. Promising #
• Do not plant alliums in ground that held alliums within 4 years, and know that the worst allium disease outlasts any rotation. Promising #
• Do not plant beets, chard, spinach or amaranth in ground that held them within 3 years. Promising #
• Do not plant brassicas in ground that held brassicas within 4 years (extension recommends 4-7, and even that is not a cure). Promising #
• Do not plant cucurbits in ground that held cucurbits within 2-3 years. Promising #
• Do not plant legumes in ground that held legumes within 3 years; the root rots build where they repeat, and the worst of them outlast any garden rotation. Promising #
• Do not plant lettuce or its family in ground that held it within 3 years, and know that lettuce drop's fungi live on most other vegetables too. A good hunch #
• Do not plant nightshades in ground that held nightshades within 3 years. Promising #
• Do not plant the carrot family in ground that held it within 3 years. Promising #
• Late blight comes back from last year's potatoes, not from the soil: tubers left in the ground carry it through winter as volunteers, so ground that grew potatoes last season needs its volunteers pulled before this year's tomatoes or potatoes go in. Promising #
• Limed ground is the wrong ground for the next potato crop: common scab worsens as soil pH rises, and lime raises it. Promising #
• On ground that has carried brassicas within the rotation interval, a measured soil pH below about 7.2 leaves clubroot's door open; raising it is the lever extension names, and the direction is all we give. Promising #

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Feeding

What the soil gives and what it needs back.

• A lime or sulfur RATE requires a buffer-pH measurement. Direction is free; the amount is not, and it is the lab's to give, never ours. Promising #
• A measured soil pH below a plant's sourced floor is worth saying out loud, with the shortfall and the direction of the fix. Above the ceiling too, but only for a plant that is documented to require acid soil — for everything else the ceiling is this corpus's own and fires nothing. A good hunch #
• Do not apply fresh high-N fertilizer to root crops. Promising #
• Fertilizer recommendations without a soil test are guesswork. Say so. Well established #
• Ground the gardener has observed to stand water after rain is a site problem to fix before planting, not a plant problem to select around. Promising #
• Legume green manure raises available N for the subsequent crop. Promising #

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Neighbours

What one plant does to the one beside it.

• A self-incompatible pome fruit's pollen partner has to bloom at the same time and make viable pollen - a triploid apple cannot be the pollen source, and a second tree of the same variety is not a second cultivar. Well established #
• An insect-pollinated crop depends on an insect to move pollen between its flowers; no arrangement of plants substitutes for one. Well established #
• Corn requires a block of at least 4 rows (roughly 12 plants) for adequate kernel set. Well established #
• Dioecious species need both a male and a female plant to set fruit. Well established #
• Do not plant a juglone-sensitive species within the root zone of Juglans. The sensitive list is the hazard's own, and it is wider than the nightshades - it also carries apple and cabbage. Well established #
• Fennel is allelopathic; a suppressive effect on neighbouring vegetables is plausible but poorly characterized (evidence is weed-directed, in vitro). A good hunch #
• Ground that just carried cereal rye or a sorghum cover crop is a poor seedbed for small seeds for a few weeks. As the residue breaks down it releases chemicals that stop small seeds germinating, and the smaller the seed the worse it fares; transplants and big seeds largely shrug it off. Promising #
• Self-incompatible species require 2+ genetically distinct plants. Well established #
• Sunflower residue suppresses germination of some small-seeded species. Promising #
• Two kinds of corn tasselling together spoil each other's kernels: sweet corn pollinated by popcorn, field or ornamental corn goes starchy, and supersweet pollinated by any other corn loses its sugar. Keep different corn types 250 feet apart or 14 days apart in tasselling. Promising #

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Climate

Where the frost and zone numbers come from, and how far they travelled.

• An observed per-plot frost offset, fitted from 3+ seasons of logged outcomes on that ground, supersedes all modelled climatology for that plot. Well established #
• Every derived climate value carries the tier, grade, station, and distance that produced it. Well established #
• Frost dates can be downscaled by applying a standard lapse rate to elevation. Well established #
• PRISM offset from a nearby station assumes the spatial pattern of mean minimum temperature predicts the spatial pattern of last-frost date. Promising #

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Advice

Cultural practice the app surfaces but never scores - it cannot see your bed.

• A basil dropped back into ground where a basil crop wilted and died young tends to do the same - growing normally to a hand's height, then stunting and suddenly collapsing - because Fusarium wilt leaves that ground infective for years, not for a season. A good hunch #
• A bed watered for its vegetables is too wet for its Mediterranean herbs. Tomato, pepper, cucumber and basil want the soil kept steadily moist, about an inch a week; rosemary, sage, thyme, oregano and lavender want it to dry between waterings. One bed gets one regime, and whichever way it is watered, half the planting suffers. Promising #
• A border of a more attractive cucurbit - blue hubbard, a Cucurbita maxima - planted a week or two before the crop and kept unbroken around it draws striped cucumber beetles to the edge, where they are dealt with, so most of the beetles, and the bacterial wilt they carry, never reach the cucumbers, melons or summer squash inside. Promising #
• A bulb ring suppresses turfgrass competition at a fruit tree trunk. Well established #
• A bulb ring suppresses turfgrass competition at the base of a woody perennial shrub or vine. Promising #
• A cole crop set out too early can bolt or "button": a long spell of cold on a young plant vernalizes it, and instead of a full head it runs to a premature flower stalk or forms a small, misshapen head. Promising #
• A container dries out faster than the same plant in the ground, and it is the one place where a day's inattention can cost you the plant. Well established #
• A direct-sown root crop left unthinned grows crowded roots that stay small - the seedlings stand far denser than they can mature, compete for the same soil, and the roots twist and intertwine instead of sizing up. Promising #
• A legume fixes atmospheric nitrogen only in symbiosis with rhizobia specific to its cross-inoculation group; ground with no recent history of that group may carry too few of them to nodulate well. Promising #
• A light sprinkle does not reach the roots. Water long enough to wet the soil to root depth, or the plant gets nothing. Promising #
• A lightweight fabric floating row cover laid over a bed at planting keeps flying and egg-laying pests off the crop through its vulnerable early stage - flea beetles, cabbage moths and loopers, cucumber beetles and squash bugs, and the root-maggot flies of cabbage, onion, and carrot - but it must come off at flowering for any crop that needs an insect to set fruit, or it excludes the pollinator too. Promising #
• A seedling raised indoors is set out gradually, not all at once: moved straight from a windowsill or grow-light into full sun and wind it suffers sunscald, windburn, or transplant shock, because its soft indoor growth has not hardened to outdoor conditions. Promising #
• A specialist pest or pathogen finds and builds on a continuous single-family host patch more readily than one broken by non-host families. A good hunch #
• A tomato transplant goes into the ground DEEPER than it grew in its pot - buried up to its first leaves - rather than at the soil line it came out of. Well established #
• A warm-season bean germinates from warm soil, not from a calendar date; sown into cold ground it rots or emerges weak, even after the frost has passed. Promising #
• A young apple or stone-fruit tree planted where an old one of its kind stood tends to sulk - stunted, uneven, sometimes dying back - because the ground an orchard tree leaves behind is not neutral for the next tree of the same kind. A good hunch #
• A young transplant can be cut off at the soil line overnight by a cutworm - a caterpillar that curls around the tender stem and severs it just above the ground. A collar around the stem blocks it. Promising #
• Allium deters borers. Contested #
• Alliums interplanted with carrots reduce carrot rust fly damage. A good hunch #
• Apple, pear and quince share fire blight, and the tree you plant decides most of the fight: choose a resistant cultivar, hold back on nitrogen, and prune strikes out well below the damage. Promising #
• Aromatic species interplanted with brassicas are reported to reduce cabbage-worm damage. The mechanism is unresolved and trial results are mixed. A good hunch #
• Basil is grown for its leaves: pinch out the growing tips and remove flower buds as they form to keep the plant making tender leaves and growing bushy. Once basil flowers, it turns toward seed and the leaves fall off in quantity and quality. Harvest and pinch from the top regularly, and take the flower buds off as soon as they appear. Promising #
• Blossom-end rot is a calcium-transport failure driven by uneven soil moisture, not a shortage of calcium in the soil. Well established #
• Blueberries need strongly acidic soil, about pH 4.0 to 5.5. Above about 5.5 the soil is not acidic enough and the plant cannot take up iron, so the new leaves yellow between the veins (iron chlorosis). Test the soil before planting; if it is too high, lower it with elemental sulfur applied several months ahead, then re-test. A foliar iron spray only greens the leaves for a while and does not fix the soil. Promising #
• Borage is an annual that self-seeds freely and returns on its own from dropped seed, so a single planting typically reappears as volunteer seedlings year after year. Expect volunteers in and around where it grew. If you would rather it did not come up, remove the spent flower and seed heads before the seed drops and pull unwanted seedlings while young; otherwise leave a few heads and let it reseed. Promising #
• Brambles pick up viruses from other brambles: aphids carry raspberry mosaic and related viruses from wild raspberries and blackberries, and from older infected plantings, into a new one. Site a new bramble planting at least 600 feet from wild brambles, and keep it away from any bramble planting that shows virus. Promising #
• Comfrey is a dynamic accumulator that mines subsoil minerals and makes them available. Contested #
• Culinary French tarragon has sterile flowers and sets no viable seed, so it is grown only from division, cuttings, or a bought started plant - never from a seed packet. Seed sold as "tarragon" is Russian tarragon, a taller, coarser plant whose flavour is far inferior. Sow that seed and you get the near-flavourless plant, not the culinary herb. Promising #
• Currants and gooseberries (Ribes) are an alternate host of white pine blister rust, and some states regulate or ban planting them - especially black currant. Check your state's rules before planting, and where white pines are nearby choose a rust-resistant cultivar. Well established #
• Do not harvest asparagus at all the first year after planting crowns. When harvest begins - the second or third spring, depending on the source you follow - keep it short: about two weeks in the first harvest year, no more than a month, then let every later spear grow out. From the fourth year on, harvest can run eight to ten weeks. After harvest ends, let the spears grow into ferns and leave them standing: the ferns are what feed the crown for next year. Promising #
• Elderberries must be cooked before eating. Raw or unripe berries - and all leaves, stems and roots - are toxic; only fully ripe, cooked berries are safe. Well established #
• Every stone fruit shares brown rot, and it overwinters on the tree: strip the mummies and prune the cankers before bud break, and keep fallen fruit picked up. Promising #
• Garlic is planted in autumn, not spring - the cloves go in the ground several weeks before it freezes, root, and overwinter. The weeks of winter cold below about 40 F vernalize the clove, and that cold is what triggers it to form a bulb the following spring as the days lengthen. Planted in spring, garlic misses the cold and bulbs poorly. Promising #
• Grapes fruit on new shoots that grow from last season's canes, and only a few well-placed canes are kept. Prune hard every dormant season - late winter, after the coldest weather but before the buds swell: removing about 80 to 90 percent of the previous year's growth is normal and necessary. Under-pruning is the common mistake and leaves a tangled vine with fewer flower buds and small, poor-quality fruit. Promising #
• How often to water is a weather question. This planner has no weather feed and will not invent a schedule. Well established #
• Insectary plants near fruiting crops increase pollinator and predator visitation. A good hunch #
• Lemon balm self-sows freely and, left to flower and set seed unchecked, spreads and can take over a bed. Cut back or deadhead the flowering stalks before they set seed to keep it in bounds, or grow it in a container. It is a strong self-seeder that can become weedy - though not a listed invasive. Promising #
• Living mulch suppresses weeds and conserves soil moisture. A good hunch #
• Mint spreads aggressively by underground rhizomes and will colonize a bed, out-competing and crowding its neighbours if grown loose in open ground. Do not plant it directly in a shared bed. Contain it in a pot, or in a bottomless container sunk into the ground, and harvest and pull strays to keep it in bounds. Promising #
• Narcissus deters voles and rodents. A good hunch #
• Nasturtiums bloom best in lean, poor-to-average, well-drained soil in full sun. Rich soil or heavy nitrogen feeding pushes the plant into lush leaf growth at the expense of flowers - the familiar 'all leaves, few blooms'. Go easy on feeding, and do not fertilise except on very poor ground. Promising #
• On a new June-bearing strawberry planting, remove every blossom for the whole first season - check weekly and pinch or cut them off; flowering stops by early July. Letting first-year flowers set fruit reduces plant growth, runner production, and the size of next year's crop. Everbearing and day-neutral types are handled differently: remove blossoms only for the first stretch after planting - about four to six weeks, or until early July - then let them fruit, with first berries from August until frost. Promising #
• Onions and garlic lifted for storage are cured first - dried down in a warm, airy, shaded place for about two to four weeks until the neck is tight and dry and the outer scales are papery. Bulbs stored uncured, or poorly cured, rot in storage instead of keeping. Promising #
• Over-feeding a tomato with nitrogen grows a tall, dark-green, leafy plant that flowers late and sets little fruit. The plant pours its resources into vines and foliage instead of blossoms, so flowering is delayed or sparse and yield drops. This is a vegetative-versus-reproductive imbalance the gardener causes by fertilizing, not the heat that makes already-open flowers fail to hold - keep the two apart. Promising #
• Potato tubers that catch light while growing - wherever soil settles or washes away and shallow tubers are left uncovered - turn green and become bitter and toxic, so the crop must be kept covered with soil rather than left exposed at the surface. Promising #
• Potatoes are grown from certified seed potatoes - disease-free seed tubers from a certified source - not from saved tubers or grocery-store potatoes. Large seed tubers are cut into blocky pieces, each with at least one eye, and the cut surfaces left to dry to a tough protective skin before planting. Grocery-store potatoes may be treated to stay dormant and can carry disease that persists in the soil. Promising #
• Raspberry and blackberry canes are biennial: a cane grows its first year (a primocane), fruits its second year (a floricane), then dies. On summer-bearing types, after harvest cut out only the spent floricanes, at ground level, and keep the current year's primocanes - they are next year's crop. Cutting every cane down on a summer-bearing plant removes next year's fruit. Ever-bearing (primocane-fruiting) types fruit on first-year canes and, grown for a single fall crop, can instead be cut wholesale close to the ground in winter. Promising #
• Rhubarb leaf blades are poisonous and must never be eaten - only the leafstalks (the petioles) are edible. Harvest the stalks and cut the leaves off. Well established #
• Rosemary, sage, thyme and oregano are Mediterranean plants that want full sun and sharp, well-drained soil and tolerate drought once established. They are intolerant of wet, heavy or poorly drained soil and are easily over-watered, which invites root and stem rot. They also do better in lean soil than rich - over-feeding grows lush, low-flavour foliage and encourages disease - so water sparingly and keep feeding light. Promising #
• Seedlings raised in cool, wet, or reused growing medium can collapse from damping-off - soil-borne fungi that rot the seed or girdle the young stem at the soil line before the plant establishes. Promising #
• Tree fruits differ in whether a lone tree can set a crop. Apples and most European pears are self-unfruitful: one cultivar alone will not set a normal crop, so plant at least two different cultivars whose bloom periods overlap - for apple, a flowering crabapple in bloom at the same time also works. European plums are partially to entirely self-fruitful, and a second European plum cultivar makes fruit set reliable - Japanese and hybrid plums will not cross-pollinate them. Peaches and sour cherries are self-fruitful and may be planted alone. Partner trees must stand near each other: the published distances are within 50 to 100 feet, and 300 feet at most. Promising #
• Water the soil, not the leaves. A film of water on a leaf is what most fungal spores need in order to germinate. Well established #

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Myths

Widely repeated, checked here, and not enforced.

• Any co-planted set of vegetables is a guild. Well established #
• Autumn olive is a good nitrogen fixer for a fruit tree guild. Well established #
• Beans fix nitrogen that feeds the corn growing beside them, that season. A good hunch #
• Marigolds interplanted among vegetables control root-knot nematodes. Refuted #

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