Garden layout, spacing and companions

Sun

Most vegetables need at least 6 hours of direct sun a day. Fruiting crops (tomatoes, peppers, squash) do best with 6–8 hours. Leafy greens and root crops can handle some shade. Full sun also dries leaves faster, and that cuts down on leaf diseases.

Desert exception: in the low-desert Southwest, pick a spot with morning sun and some afternoon shade.

Beds

• Width: 3–4 ft, as long as you like. If you can only reach one side, make it about 2 ft wide.

• Height: 8–12 in is common. On decent soil, about 4 in of raise is enough. Where the native soil is poor, build at least 8–12 in of good soil.

• Why raise them: they drain better and warm up faster in spring.

• No-dig option: no-dig gardeners use beds about 4 ft wide and up to 5–6 ft. They accept stepping on them now and then.

Paths

Published path widths range from 15–18 in (no-dig) to 18–24 in (Colorado State) to 2–3 ft (Mel Bartholomew) and 3 ft (UF square-foot gardens). No study tests path width. Use the narrowest path that lets you kneel, turn a wheelbarrow, or use a walker or wheelchair if you need one.

Which way to face beds and where tall crops go

• Default: put tall crops (corn, okra, sunflowers, staked tomatoes) and trellises on the north side so they don't shade shorter plants. NC State recommends running rows north to south.

• Hot desert summers: do the opposite on purpose. Put tall crops or trellises on the west or south side to shade crops from afternoon sun, or use 30% shade cloth, which cools plants by 4–5°F.

• Shade-loving greens (lettuce, spinach) can grow on the shady side of tall crops.

Frost pockets

Cold air flows downhill like water. Low spots and valley floors frost earlier in fall and later in spring than nearby slopes. A south-facing, gentle slope warms first in spring and frosts last in fall.

Equidistant spacing

In a bed, set each plant the same distance from all its neighbors. Stagger every other row so plants sit between the plants in the next row. When the leaves meet, they form a "living mulch." It shades out weeds and slows water loss.

This only works in fertile, weed-free, well-drained soil with lots of organic matter. Crowd plants past the spacing below and they stay damp, so disease spreads.

Spacing table

Bed spacing is the distance between plants in every direction, from three extension guides. Square-foot count is plants per 1-ft square, from the Square Foot Gardening Foundation unless noted.

Traditional rows need much more room. UF/IFAS minimum distances between rows: carrots 10 in, bush beans and lettuce 18 in, corn 28 in, potatoes 36–42 in, cucumbers and tomatoes 48 in. UF adds that row spacing "can be reduced or ignored" when plants are spaced correctly in beds.

Square-foot gardening in brief

• Build a frame 4 × 4 ft, 6–8 in deep, and lay a grid of 1-ft squares on top.

• Fill it with compost alone, or equal thirds of compost, peat moss and coarse vermiculite.

• Plant 1, 4, 9 or 16 plants per square, which works out to 12, 6, 4 or 3 in apart.

• To choose a count for any crop, look at the seed packet's "thin to" distance.

• When a square finishes, add a scoop of compost and plant something different in it.

Example 4 × 4 ft bed (one possible layout built from the rules above; north is at the top):

Interplanting: using the gaps

Tuck fast crops (radish, leaf lettuce, spinach, green onions) into the gaps around slow, big crops (peppers, broccoli, tomatoes). They're harvested before the big plants fill in. UNH's example: peppers at 12 in apart leave room between them for radishes, leaf lettuce or spinach.

Spacing two crops side by side: add their spacings and divide by 2. Radishes (2 in) next to beans (4 in) gives (2 + 4) ÷ 2 = 3 in.

Succession planting: a steady harvest

Sow small batches of quick crops again and again instead of all at once. University of Kentucky's intervals:

• Rule of thumb: make the gap about as long as one planting keeps producing.

• Spring: leave longer gaps between early sowings in cold soil, and about 10 days between the last ones.

• Another way to spread the harvest: plant several varieties with different maturity dates at once, such as 50-day and 60-day beans or early, mid and late sweet corn.

• Swap crops as the season turns: cool-season peas, lettuce or broccoli in spring, then beans, tomatoes or peppers in the same spot; corn after peas.

What the evidence says overall

Traditional "friends and enemies" charts **have no scientific basis as a system*. Many trace back to astrology-era plant lore, or to a lab method called "sensitive crystallization" that was the basis for the book Carrots Love Tomatoes*.

In a West Virginia University trial, the pairs the charts recommend and the pairs they warn against used land equally well.

Mixing crops can still pay off. It just works through timing, density and a few proven mechanisms, not through "friendship".

Works: mixing crops with different timing

Across hundreds of field studies, growing two crops together produced an average of 22% more food per area than growing them separately (Land Equivalent Ratio 1.22). Most of the gain comes when the crops are planted or harvested at different times.

Garden results vary. In WVU trials, basil grown with tomatoes or Brussels sprouts gave about a 20% advantage, and tomatoes with Brussels sprouts gave none.

The catch: plants in a mix compete for light, water and food.

• In NDSU trials, hairy vetch sown under cabbage too early cut cabbage yield 47%. Sown later, it did no harm.

• ATTRA suggests 10–30% more fertilizer for mixed plantings, a bit less seed of each crop, and crops that mature at different times.

Works: trap crops

A trap crop is a sacrificial plant that pests like better than your crop. You plant it around the crop, let the pests gather on it, then kill the pests on the trap by hand-picking, spraying only the trap, or pulling it.

University of Connecticut trials:

• Collards around cabbage: 56% fewer insecticide sprays.

• Cherry peppers around bell peppers: at least 98% pest-free fruit, and up to 89% less insecticide.

• Blue Hubbard squash around summer squash: over 94% of cucumber beetles stayed in the border. Beetles on the main crop fell by up to 95%. Spraying only the border cut squash vine borer in the main crop by 88%.

Proven pairs:

How to do it:

1. 1

   Plant the trap 3–4 weeks before the main crop when you can.

2. 2

   UF/IFAS puts perimeter traps at least 5 ft from the crop. UConn surrounded the crop completely, "like fortress walls".

3. 3

   Check the trap several times a week.

4. 4

   Deal with the pests once they've gathered on the trap, before they move to your crop.

Works: flowers for pest-eating insects

Small, open flowers feed hover flies and tiny parasitic wasps that attack aphids, caterpillars and other pests. Good choices are sweet alyssum, buckwheat, dill, coriander (cilantro), lacy phacelia, bachelor's button and yarrow.

• Many parasitic wasps travel only a few hundred feet, so put flowers in or right beside the garden.

• Buckwheat flowers 30–45 days after sowing, and you can fit two sowings in a summer. Mow it before it sets seed.

• Phacelia dies at 20°F. Sow it in spring in cold climates and in fall in warm ones.

• Honest caveat: these flowers reliably bring more beneficial insects, but the effect on harvest size is "less well known".

Works for corn, beans and squash, with a twist: the Three Sisters

In Cornell field trials, corn, beans and squash grown together produced more total food energy and protein per acre than any one of them alone, or the same land split into separate plots. Corn yield held steady.

But beans fell to about 9% and squash to about 26% of what they yield grown alone. A study with the Catawba Nation found corn alone gave more corn and more food per hour of work.

Grow the Three Sisters for total food and tradition. Don't expect full bean and squash harvests.

Mixed evidence: herbs and flowers as repellents

University of Minnesota cites research for several pairings:

• Basil or marigolds reduced thrips on tomatoes.

• Nasturtiums reduced squash bugs.

• Thyme, onion or nasturtium reduced cabbageworm damage on broccoli.

• Sage and thyme reduced diamondback moth on Brussels sprouts (greenhouse trials).

Other researchers found aromatic herbs had little or no effect in their trials. Try these if you like, but don't rely on them.

Doesn't work (or isn't proven)

Marigolds and nematodes: the right way

Root-knot nematodes are tiny worms that knot up roots. Marigolds only help when you grow them as a crop in their own right:

1. 1

   Get a nematode soil test first.

2. 2

   Plant a dense, weed-free stand* of French (Tagetes patula) or African (T. erecta*) marigolds, under 7 in apart**, right where next season's crop will go.

3. 3

   Let them grow at least 2 months, then turn them in. Only living roots release the compound that works. Chopped plants and extracts do nothing.

4. 4

   Repeat every season before the crop. Marigolds don't wipe nematodes out.

Watch out:

• Marigolds can increase other nematode types (stubby-root, spiral, sting, awl).

• Signet marigolds don't work at all against root-knot.

• Cost in 2007 was over $20 per 100 sq ft for transplants.

Plants that harm other plants

• Black walnut releases juglone from its roots, leaves and hulls.

  • Sensitive crops: tomatoes, potatoes, peppers, eggplant, asparagus, cabbage, rhubarb.
  • Tolerant crops: beans, beets, carrots, corn, melons, onions, parsnips, squash.
  • Damage is worst near the drip line, and roots reach past it. Keep sensitive crops 50–60 ft from the trunk of a mature tree.
  • Juglone keeps coming from the roots until they rot, which can take 5 or more years after the tree is removed.
  • Don't mulch with walnut leaves, bark or chips. Compost them at least 6 months; sources disagree on how long. To check finished compost, grow a few tomato seedlings in it. They wilt if juglone remains.

• Cereal rye residue cut weeds 78–99% in trials. It also stunts small seeds. Wait 3–4 weeks after killing rye before sowing carrots or onions. Transplants and big seeds handle it better.

Three groups of crops

Some tomatoes with protruding flower parts, and older heirlooms, cross more readily.

The two big myths

1. 1

   "Cucumbers next to squash or melons will make them taste bad." False. Only plants of the same species can cross. Cucumbers, muskmelons, watermelons and squash are all different species. Bad-tasting melons and cucumbers usually come from weather or soil problems.

2. 2

   "My zucchini crossed with a pumpkin, so this year's zucchini is ruined." False. A cross changes the seeds inside the fruit, not the fruit itself. The fruit you eat this year looks and tastes normal. Only plants grown from those saved seeds will be different.

Squash species: who can cross with whom

Squash only cross within their species. Crosses between species are rare.

So a zucchini and an acorn squash will cross, but a zucchini and a butternut almost never will. If you need guaranteed pure seed, hand-pollinate (below).

Corn is the exception

Corn shows a cross in this year's ears:

• Field corn or popcorn pollen makes sweet corn starchy and tough.

• Supersweet (sh2) corn crossed with any other sweet corn type ruins both.

• Yellow pollen puts yellow kernels in white corn. It changes the look, not the eating quality.

Keep types apart (protects this year's harvest):

Plant upwind of other corn if you can. A heat wave or cold spell can shift flowering, so distance is safer than timing.

Plant corn in a block. Use at least 4 short rows side by side, not one or two long rows. Pollen falls from the tassels onto silks nearby; a single row loses its pollen to the wind and gives ears with missing kernels.

Corn spacing: in rows, seeds 8–12 in apart with rows 2½–3 ft apart (Iowa State). In a bed, intensive spacing is about 12 in each way, so a 4-ft bed holds a 4-row block.

Saving seed: isolation distances

These distances keep saved seed true to variety. They are much bigger than the eating-quality distances above. Sources disagree widely. Below is the Seed Savers Exchange 2017 chart, which University of Illinois Extension reprints.

Other figures for corn run from 1,600 ft to 2 miles. A peer-reviewed field study found under 1% crossing beyond about 65 ft (20 m). Beets and chard are the same species and will cross. Both flower in their second year.

When you can't get the distance:

• Timing: stagger plantings so flowering doesn't overlap. This is used mainly for corn.

• Bags or cages: cover flowers or whole plants with fabric. Caged crops that need insects require hand pollination, or bees inside the cage.

• Hand pollination: see below.

Hand-pollinating squash for pure seed

1. 1

   Evening: find a male flower (on a long stem) and a female flower (with a tiny squash at its base) that are just turning yellow and will open tomorrow. Tape or tie each one shut.

2. 2

   Next morning, after the dew dries: pick the male flower and peel off its petals.

3. 3

   Open the female, brush the male's pollen onto the center, and close the female again right away. SDSU says to do this within 4 hours of the female opening. Using pollen from 3 or more males keeps more genetic variety.

4. 4

   Tag the stem loosely so you save seed only from that fruit.

Pollinators and fruit set

• Squash, pumpkins, cucumbers and melons need insects. Each flower opens for one day only.

• Cucumbers need at least 9 bee visits per flower. Poor pollination gives small or misshapen fruit.

• Early in the season many vines make only male flowers. In muskmelons, the females follow 10–14 days later.

• Parthenocarpic varieties set fruit with no pollination. They're useful under insect netting or in a greenhouse.

• Protect bees: don't spray plants in bloom. If you must spray, do it after dusk and not on dewy leaves. Even organic sprays like pyrethrins and spinosad are highly toxic to bees.

Heat stops fruit set

Time flowering to miss the hottest weeks. In hot regions that usually means separate spring and fall crops.

Hot and sweet peppers

Jalapeños and bell peppers are the same species and cross easily. A habanero is a different species and is unlikely to cross with them. Like squash, a cross **doesn't change this year's peppers*, only plants grown from saved seed. For pure seed, treat all peppers as able to cross. Medium confidence:* no pepper-specific Tier 1 statement on the current-year point was found.

How legumes really add nitrogen

Beans, peas, clover and vetch host bacteria in root nodules that pull nitrogen from the air.

• Check the nodules: split one open. Pink or red inside means it's working. White, gray or green means little or no fixing.

• When: nodules show up 2–3 weeks after planting.

The common myth is that beans fertilize the plants around them. They mostly don't:

• The nitrogen goes into the plant, and most of it leaves with the harvested beans or peas.

• Bean leftovers are ordinary. Bean residue holds about as much nitrogen as any other crop residue.

• Garden beans are weak fixers. They fix under 50 lb N/acre, less than they need themselves.

• Better fixers: cowpeas, fava beans and soybeans fix up to 250 lb/acre. Clovers and vetches fix 250–500 lb/acre.

• Neighbors get little. Living legumes pass only a little nitrogen to their neighbors during the season; most of it is released after the legume dies and rots.

To actually build nitrogen: grow a legume cover crop and return the whole plant to the soil, ideally at early to full bloom, when nitrogen peaks.

• Field peas turned in mid-season left about 80 lb N/acre, versus just over 30 lb after harvesting the peas.

• Killing crimson clover a month too early costs up to 50 lb N/acre.

Inoculate: the first time you grow a legume in a bed, coat the seed with the matching rhizobia inoculant. It's cheap insurance. Legumes fix poorly in acid, wet, or low-phosphorus/potassium soil.

Cover crops for garden beds

Rates per 100 sq ft are for hand-broadcast gardens (Purdue). Farm rates are much lower.

Timing:

• Sow: rye late summer to mid-fall in zones 3–7, and fall to midwinter in zones 8+. Crimson clover 6–8 weeks before first frost. Hairy vetch 30–45 days before a killing frost. Oats for winterkilled mulch 40–60 days before first killing frost.

• Kill: 2–4 weeks before planting. Wait 3–4 weeks before small seeds after rye. Always before the cover sets seed.

• Mixes: rye alone ties up nitrogen as it rots, more so the older it gets. Kill it young or mix it with vetch.

Crop rotation by family

Don't grow the same plant family in the same soil more than once every 3 years; 4–5 is better.

What rotation can't do:

• It doesn't stop diseases blown in on the wind, or pests that overwinter on weeds.

• It does little against long-lived soil diseases that attack many families: Southern blight, Fusarium and bacterial wilt, Phytophthora, Pythium, Rhizoctonia and root-knot nematodes. These are worst in warm Southeast soils.

Make rotation work:

• Use separate beds. Tilling one big plot all at once moves diseased soil between your "zones". With four beds, each family comes back to the same bed only every 4 years.

• Count cover crops. They're part of the rotation too. Rye and oats are grasses like corn.

• Use containers. Disease-prone crops like heirloom tomatoes can go in containers, outside the rotation.

"Heavy feeder → light feeder → soil builder" is a popular order. It has a reasonable nutrient logic (squash use lots of nitrogen, onions more potassium), but no trials test the sequence, and published versions disagree. Rotating by family is what the evidence supports.

Is rotation always needed? UK no-dig grower Charles Dowding grew the same crops in the same beds for 8 years with strong yields, using compost every year. That's one cool-climate garden with clean soil. In warm, humid regions with soil diseases, rotate.

Organic matter

Work in a 1–2 in layer of well-rotted compost before planting (NMSU). Colorado State uses 1 in of compost for every 4 in of soil depth. Mix in uncomposted material at least a month before seeding.

Manure safety intervals before harvest are covered in the Manure management lesson.

Sample four-bed rotation

This is an example built from the rules above, not a published plan. Each bed takes one group per year and moves one step each year.

• Each family returns to the same bed every 4 years.

• The legume year is when you grow and turn in a cover crop for nitrogen.

• Surround the squash bed with Blue Hubbard as a trap crop.

• Plant the corn as a block of at least 4 rows.

Costs: not yet researched. The only sourced cost is marigold transplants for nematode control, over $20 per 100 sq ft at 2007 prices.

1. 1

   Planting one long row of corn. Ears come out patchy. Plant a block.

2. 2

   Crowding plants past the recommended spacing. It brings more disease, especially in humid summers.

3. 3

   Stepping on bed soil. It compacts the soil. Keep beds narrow enough to reach the middle.

4. 4

   Trusting a companion chart over spacing and timing. The chart has no evidence behind it; competition does.

5. 5

   Scattering marigolds for nematodes. It doesn't work. Grow a dense stand ahead of the crop instead.

6. 6

   Expecting bean rows to fertilize the next crop. The nitrogen leaves with the harvest; use a turned-in cover crop instead.

7. 7

   Letting cover crops go to seed. Vetch and buckwheat become weeds.

8. 8

   Sowing carrots right after rye. Wait 3–4 weeks.

9. 9

   Rotating "zones" inside one tilled plot. Tilling spreads the disease you're trying to starve. Use separate beds.

10. 10

    Saving seed from squash grown near other squash of the same species. The seed won't come true. Hand-pollinate instead.

11. 11

    Spraying blooming plants in the daytime. It kills bees; spray after dusk if at all.

12. 12

    Planning by hardiness zone alone. Zones don't give frost dates. Use local frost tables.