Where the Square Foot Gardening Charts Disagree
Almost every gardening site publishes one spacing chart as if the numbers were settled. They are not. We read 3 published charts in full and found disagreements of up to 16x on the same crop - and one source that contradicts itself. Here is all of it, side by side, with sources.
Data reviewed: . Plant spacing, companion and sow-date data are checked against university-extension sources; this date changes only when we actually re-verify.
The short answer
For about two thirds of common crops all three charts agree exactly, and you can stop worrying. The disagreements cluster in a predictable place: crops you might harvest young or leave to mature (mustard, chard, basil, beets), and bulb crops where spacing decides size (onion, garlic, leek). In those cases the chart is not wrong, it is answering a different question from the one you are asking.
The charts we compared
SFG Foundation
The method's own governing body
Square Foot Gardening Foundation, "Square Foot Spacing" (the organization Mel Bartholomew founded)
Read the sourceRead in full 2026-09-21
Clemson Extension
Land-grant university extension service
Clemson Cooperative Extension, Home & Garden Information Center, "Small-Scale Gardening", Sample Planting Guide
Read the sourceRead in full 2026-09-21
Phipps Conservatory
Botanical garden education program
Phipps Conservatory and Botanical Gardens, "Square Foot Gardening Guide" (2020), Square Foot Planting Chart
Read the sourceRead in full 2026-09-21
The disagreements, largest first
Plants per square foot, exactly as each chart states it. A dash means that chart does not publish a figure for that crop, which is itself worth knowing. Our own number is in the last column so you can see where we landed and disagree with us if you want to.
| Crop | SFG Foundation | Clemson Extension | Phipps Conservatory | Spread | This site |
|---|---|---|---|---|---|
| Mustard greens | 1 | 16 | 9 | 16x | not carried |
| Chives | 16 | 9 | 2 | 8x | 16 |
| Onion (bulb) | 16 | 4 | 9 | 4x | 9 |
| Garlic | not listed | 4 | 16 | 4x | 9 |
| Dill | not listed | 1 | 4 | 4x | not carried |
| Celery | 4 | 1 | not listed | 4x | 4 |
| Leeks | 9 | 4 | not listed | 2.3x | not carried |
| Basil | not listed | 4 | 2 | 2x | 4 |
| Swiss chard | not listed | 4 | 2 | 2x | 4 |
| Beets | 9 | 9 | 16 | 1.8x | 9 |
| Turnips | 9 | 8 | not listed | 1.1x | not carried |
| Tomato | 1 | 1, with a cage | 1 per 2ft x 2ft block | see note | 1 |
| Summer squash / zucchini | Bush varieties need 9 whole squares; vining varieties 2 squares | 1 per square, with a stake | 1 per 3ft x 3ft block | see note | 1 |
Why each one differs
Mustard greens
The widest gap of any crop, and it is a definitional one: harvested as full mature plants they need a square each, harvested as cut baby leaves they do not. None of the three charts says which it assumes.
Chives
Chives grow as an expanding clump, so "one plant" is ambiguous - a 16-per-square reading counts seedlings, a 2-per-square reading counts established clumps a few seasons on.
Onion (bulb)
Bulb size is the trade-off. Closer spacing yields more onions of smaller size; the extension figure targets a full-size bulb. This is also the crop the Foundation contradicts itself on - see below.
Garlic
A four-fold gap with no stated reason. 16 per square foot is 3in spacing, which is tighter than most garlic guidance anywhere.
Dill
Dill grown to full height and seed head needs the room; dill cut young for leaf does not.
Celery
A four-fold gap on a crop that is genuinely large at maturity.
Leeks
Same trade-off as onion: leek thickness responds directly to spacing.
Basil
Pinched repeatedly for leaf, basil stays small; left to grow it becomes a shrub.
Swiss chard
Cut-and-come-again harvesting supports the tighter figure.
Beets
Two of three agree at 9. Phipps is tighter, which suits baby beets and beet greens.
Turnips
A rare near-agreement. Clemson's 8 is not a standard grid number, which is itself a hint that these charts are not derived from one another.
Tomato
The numbers look identical and are not. Phipps gives a tomato FOUR square feet, not one. That is the single biggest practical difference in the whole comparison and it is hidden by the units.
Summer squash / zucchini
A nine-fold spread between the Foundation and Clemson for the same plant. Staking or trellising is what changes the answer, and only Clemson says so in the chart itself.
Go deeper, one crop at a time
Each crop guide puts every source for one crop side by side, in their own words, with bed counts and a plan you can open in the planner.
The Foundation contradicts itself on onion
This is the part worth knowing if you have ever been told there is one official number. Both of these pages are live on the Square Foot Gardening Foundation's own website, both were written by the same author, and they do not agree.
Square Foot Spacing
16 per square, flat
Small-sized crops are grown three inches apart and include carrots, chives, onions, and small radish varieties. (16 plants per square)Read it
What to Plant in Spring
9 for bulbing, 16 for bunching
Sow onion seeds 1/4 inch deep, four to six weeks before the last average frost, at a spacing of 9 per grid section for bulbing onions, and 16 per section for bunching onions.Read it
Both are defensible. A bunching onion harvested young really does fit 16 to a square; a storage onion that needs to swell really does not. The summary chart flattens a size-dependent answer into one number, and the crop guide keeps the distinction. The problem is only that the summary chart is the one everybody copies.
The rule that explains most of the confusion
Square foot spacing is not a rival theory of how plants grow. It is one arithmetic step applied to a number you already have. The Foundation states it plainly:
Inspect your seed packet - it should say "thin to X inches apart." Once you have the "thin to" number, you can refer to the chart listed above. If the seed packet recommends thinning to three inches apart, then you can consider it a small plant and sow or plant 16 per square foot.
Take the seed packet's "thin to" distance, apply it in both directions, and delete the walkway. A 3 inch crop gives 4 across and 4 down, so 16 per square foot. A 6 inch crop gives 2 by 2, so 4. That is the whole method:
- 12 inches apart = 1 per square foot (Extra large): broccoli, brussels sprouts, cabbage, cauliflower, collards, eggplant, kale, mustard greens, okra, peppers, sweet potatoes, vine tomatoes
- 6 inches apart = 4 per square foot (Large): bok choy, celery, corn, leaf lettuce, parsnips, potatoes
- 4 inches apart = 9 per square foot (Medium): beets, bush beans, leeks, spinach, turnips
- 3 inches apart = 16 per square foot (Small): carrots, chives, onions, small radish varieties
This matters for a reason most comparisons miss. When a university extension says a crop needs "3 inches apart in rows 18 inches apart", it is not contradicting the 16-per-square figure. It agrees on the plant and differs only on the aisle, because a field row needs somewhere to walk and a raised bed you reach across does not. Comparing a row number to a bed number produces a disagreement that was never there. The genuine disagreements are the ones in the table above, where two bed charts differ.
Where all three charts agree
The honest other half of the story. For these crops every chart that lists them gives the same number, so you can plant them with confidence and stop reading.
Does packing plants tighter actually cost you anything?
Yes, and it is a trade rather than a mistake. The consistent finding across university guidance is that closer spacing raises yield per square foot and lowers yield per plant. More onions, smaller onions. More cabbages, smaller heads. If you are growing for the kitchen that is usually a good trade. If you want one prize marrow it is a bad one.
The second effect is airflow. Several extension services warn that dense planting reduces air circulation and raises disease pressure, and it is climate-dependent: it matters far more in a humid summer than a dry one. The most convincing statement of this comes from the Foundation itself, which is hard to dismiss as an outsider misreading the method:
I choose to plant my favas on the dense side (four inches apart) because my climate is dry and I don't tend to have issues with fungal pathogens.
So the practical rule is not "follow the chart". It is: start at the looser end of the published range, and tighten as your soil improves and you learn what your climate forgives. That is also, notably, what the tighter charts assume you have already done.
What we could not verify
Stating this plainly because a comparison page that hides its gaps is not worth trusting:
- Mel Bartholomew's books are not quoted here. We could not open either edition during this research, so no figure is attributed to them. Several sites quote the books confidently; we are not repeating a number we have not read.
- No controlled trial of square foot gardening densities appears in the literature we searched. The yield trade-off above rests on general plant-density research and extension guidance, not on a study of this method specifically. If one exists, we have not found it.
- Two claims circulating online were checked and dropped. One widely repeated disease quote attributed to a university extension is not on that page at all. We are not passing it on.
Use the numbers
Our full chart gives a per-square figure, in-row spacing and days to harvest for every crop we carry. The planner applies them to a bed of any size and adds up what fits.
Questions
Which square foot gardening spacing chart is correct?
There is no single correct chart, and that is the honest answer. The Square Foot Gardening Foundation, Clemson Cooperative Extension and Phipps Conservatory all publish charts under the same method and disagree on more than a dozen crops. For most crops the differences are small or explained by how you intend to harvest. Where they differ widely, the looser number is the safer default in a humid climate and the tighter number gives more, smaller produce.
How many onions can you plant per square foot?
Between 4 and 16, depending on which authority you follow and what size onion you want. The Square Foot Gardening Foundation says 16 on its spacing page but 9 for bulbing onions on its own spring planting page. Clemson Extension says 4 for bulb onions and 16 for green onions. Phipps says 9. If you want full-size storage onions, the lower numbers are the ones to follow.
Why do the charts disagree so much on mustard greens?
Because they are answering different questions. One square per plant assumes you are growing mustard to full mature size; 16 per square assumes you are cutting baby leaves for salad. Neither chart states which it assumes, which is what makes the gap look like a contradiction rather than a choice.
Where does the square foot gardening spacing actually come from?
From seed packets. The Foundation states the rule plainly: take the "thin to X inches" figure from the packet and apply it in both directions, with no walkway. That is why a 3 inch crop becomes 16 per square foot and a 6 inch crop becomes 4. It also means most apparent conflict with university row-spacing guidance is not real conflict, because the extension figure includes an aisle to walk in and the square foot figure does not.
Is tighter spacing actually worse for the plants?
It is a trade-off rather than a mistake. Closer spacing raises yield per square foot and lowers yield per plant, so you get more onions of smaller size. The real risk is airflow: several extension services warn that dense planting reduces air circulation and can increase disease pressure, and it matters more in a humid climate than a dry one. The Foundation itself makes the same point about its own beds.
What spacing does this site use?
We publish our own number for every crop and say where it sits against the sources. Where the sources split we have generally taken the middle figure rather than the tightest one. Two of our values are deliberately not the canonical number: peas and pole beans are 8 per square foot in every published chart, and our planner grid only supports 1, 4, 9 and 16, so we round them to 9. That rounding is ours, not the method.
Sources
- Square Foot Gardening Foundation, "Square Foot Spacing" (the organization Mel Bartholomew founded). View the source (read in full 2026-09-21)
- Clemson Cooperative Extension, Home & Garden Information Center, "Small-Scale Gardening", Sample Planting Guide. View the source (read in full 2026-09-21)
- Phipps Conservatory and Botanical Gardens, "Square Foot Gardening Guide" (2020), Square Foot Planting Chart. View the source (read in full 2026-09-21)
- Every figure on this page was read from the raw text of the source document on 2026-09-21, not from a search summary or a secondary blog. Where a source omits a crop we say so rather than filling the gap from elsewhere.