Bean spacing and seed rate per acre are one calculation, not two numbers to look up. Ugandan extension material puts bush beans at 50 cm between rows and 10 cm between plants, which fills an acre with roughly 80,900 plants, and the seed weight that fills those holes runs from about 25 to 40 kg depending on how large your variety's grain is. Seed size decides the rate.
That last point is where most published figures go wrong. Three Ugandan documents give three different seed rates for beans, and readers treat the difference as a contradiction to be resolved by picking a favourite. It is not a contradiction. Work the arithmetic and all three fall into place, because a kilogramme of small seed holds far more planting units than a kilogramme of large kidney grain.
What an Acre of Beans Actually Holds
An acre is about 4,047 square metres. Every spacing you choose carves that area into a number of planting stations, and the plant population follows directly. No source is needed for this part; it is division.
At 50 cm between rows and 10 cm within the row, each plant gets 0.05 square metres, so the acre holds about 80,900 stations. Uganda's Bean Cultivation Handbook, produced by the Alliance of Bioversity International and CIAT under the CGIAR Seed Equal initiative with guidance from the Ministry of Agriculture, Animal Industry and Fisheries, gives the figure as approximately 80,200 plants per acre. The two agree closely enough that you can trust either.
Turning Bean Spacing Into a Seed Rate Per Acre
Once you know how many seeds go in the ground, the seed rate is a weight question. Bean seed is sold and described by the weight of 100 seeds, and NARO publishes that figure for its released varieties, which makes the calculation exact rather than approximate.
Multiply your plant population by the weight of one seed. NABE 20 is recorded at 41 g per 100 seeds, so 80,900 plants need about 33 kg. NABE 22 sits at 42 g per 100, giving about 34 kg. NABE 18 is described as large seeded at 49.3 g per 100 seeds, and the same acre at the same spacing then wants close to 40 kg. Run it the other way for a small seeded line at 31 g per 100 and you land near 25 kg.
Nothing about the spacing changed across those four figures. Only the grain did.
Why Three Ugandan Bean Seed Rates Disagree
Here is the disagreement, stated plainly rather than smoothed over. The Bean Cultivation Handbook gives 25 to 30 kg of seed per acre. NARO's bean training manual from Ngetta Zonal Agricultural Research and Development Institute gives 32 kg per acre for bush beans in one line and 32 to 36 kg per acre two lines later. The NARO good agronomic practices poster for beans prints a plant density of 30 to 40 kg with no unit of area attached at all.
Both of the first two documents recommend the same 50 cm by 10 cm spacing. So the seed rates cannot be describing different plant populations. Convert each into an implied 100 seed weight and the pattern appears: 25 to 30 kg per acre corresponds to seed of roughly 31 to 37 g per 100, while 32 to 36 kg corresponds to roughly 40 to 44 g per 100. NARO's own variety records put the released Ugandan market classes at 41 to 49.3 g per 100 seeds.
Read that way, the handbook's band is sized for small and medium grain, NARO's band is sized for the medium to large grain that dominates Ugandan markets, and neither reaches far enough for a genuinely large seeded line like NABE 18. Both are correct inside their own assumption. Neither is a national constant.
The poster is a different case. An unlabelled seed rate looks unusable, and an earlier reading of it treated the figure as lost. Test the two candidate units and it recovers. Per hectare, 30 to 40 kg spread over the 250,000 to 333,000 plants its own spacing implies would mean 9 to 16 g per 100 seeds, below any bean grown anywhere. Per acre, it means 22 to 40 g per 100 seeds, which is the real range for beans. The unit is per acre, and the arithmetic proves it.
Bush Bean Spacing: Two Ways to the Same Plant Population
For bush types the Bean Cultivation Handbook offers a choice that is more interesting than it first looks. Plant at 50 cm by 10 cm with one seed per hole, or at 50 cm by 20 cm with two seeds per hole. Those give 80,900 plants either way, from 80,900 holes in the first case and 40,500 in the second.
Same population, same seed weight, half the digging. The catch is that a doubled hole puts two seedlings in one spot competing for the same water in the first fortnight, and a failed hole loses two plants rather than one. NARO's manual recommends one plant per station at 50 cm by 10 cm, then says to sow two seeds per hole and thin back to one where seed quality is doubtful. That is the same tool used for a different purpose: insurance against poor germination rather than a labour saving.
Line planting is not decoration. Both documents ask for rows marked with string or a line marker, because rows are what make weeding, scouting for pests and diseases, spraying and harvesting possible at all. Broadcast beans cannot be walked through without treading on the crop, and the yield loss shows up later as an unweeded field rather than as a spacing problem.
Climbing Bean Spacing and the Population Nobody Has Settled
Climbing beans are where the published figures genuinely diverge, and no amount of arithmetic closes the gap, because the recommendations differ in what they are trying to achieve.
NARO's bean training manual gives 50 cm by 20 cm for climbing beans in pure stand, which is 40,500 plants per acre, and pairs it with a seed rate of 16 kg per acre. Check that against the grain: 16 kg over 40,500 seeds works out at about 40 g per 100 seeds, right inside the measured range for Ugandan bean varieties. The two figures reconcile exactly, which is good evidence they are real rather than transcription slips.
NARO's climbing bean leaflet, covering NABE 12C, NABE 26C and NABE 29C, recommends 50 cm by 20 cm or 60 cm by 20 cm at one seed per hole, then states a seed rate of 40 to 50 kg per hectare "at 50 cm by 10 cm", a spacing it never recommends anywhere on the page. Work that combination and it demands seed of 20 to 25 g per 100, roughly half the weight of any released Ugandan bean. The spacing quoted in the seed rate line is a misprint; the recommendation in the spacing section is the one that adds up.
Ugandan research goes denser still. Work from Makerere University in Kabale district used a pure stand climbing bean population of 111,111 plants per hectare. The research best bet tested with farmers in Kabale, Kanungu and Kapchorwa districts used 50 cm rows and 25 cm within the row at two seeds per hole, a density of 160,000 plants per hectare, alongside 40,000 stakes per hectare and stakes taller than 1.75 m. Regional technology profiles circulate a figure near 200,000 plants per hectare.
So the honest answer spans roughly 83,000 to 200,000 plants per hectare, which is about 34,000 to 81,000 per acre. Anyone quoting a single climbing bean population for Uganda has chosen one document and not said so.
Stakes Set the Real Limit on Climbing Bean Density
The reason that range stays open is not agronomy. It is stakes.
NARO's climbing bean leaflet says to place one strong stake about 2 m long between two plants, or in the centre of four plants. Those two arrangements differ by a factor of two in how many plants a given stake count can carry. At 40,000 stakes per hectare, two plants per stake supports 80,000 plants and four plants per stake supports 160,000. Which means the plant population you can honestly recommend sits downstream of the staking material a farmer can actually find, and the research best bet treated four plants per stake as its upper limit.
Staking timing is more settled than staking density. Put the stakes in two weeks after germination, when tendrils begin to form, placed between the crop rows. NARO's leaflet puts it at two to three weeks after planting and pairs it with the first weeding, which saves a pass through the field. Stakes can be stored and reused across seasons, and both documents tell you to lift them at harvest rather than leave them in the ground.
What Ugandan Farmers Actually Plant
A spacing recommendation is a proposal. The measurement of what happens next is unusually good for Uganda, because the highland climbing bean work recorded plant density, stake density, seeds per hole and stake length on farmers' own plots in the season after the demonstration.
Out of 177 farmers, two used all seven monitored practices. Ninety nine percent changed something, and every one of them kept at least one practice. The average number of practices in use during the trial season was 3.8, falling to 2.8 the season after. Seeds per hole and plants per stake were both commonly higher than demonstrated.
Density moved in both directions. Farmers in Kanungu and Kapchorwa planted more thinly than the 160,000 plants per hectare demonstrated, while Kabale farmers averaged 235,000, well above it. Stake numbers went the other way in every district: a quarter of farmers matched the demonstrated stake count, with district averages of 27,000 to 34,000 stakes per hectare against the 40,000 shown. Average stake length was 1.60 m in Kabale against 1.74 m in Kanungu and Kapchorwa, and only a fifth of Kabale farmers reached the 1.75 m mark.
Fewer, shorter stakes carrying more plants each is the pattern. It is the rational response to a stake shortage, and it tells you which half of a climbing bean recommendation is fragile.
Spacing Beans in an Intercrop, and What the Maize Costs You
Most Ugandan beans are not grown in pure stand, so intercrop spacing is the real question for many readers. The Bean Cultivation Handbook says bush beans can go with maize, sorghum, coffee, cassava or banana, that spacing should be adjusted to the recommendation for the mixture, and that beans do poorly under heavy shade. Climbing beans are better as a sole crop, because they grow fast enough to smother maize.
Ugandan field data puts numbers on the trade. In work at Kabale, mixing climbing beans with maize cut bean yield by 63 percent in one season and 71 percent in another, and the loss tracked a fall in pods per plant of 39 and 33 percent. Maize itself gave 32 percent less in the mixture than in sole stand in one of those seasons. The best bean yield in the trial, about 1.075 t per hectare, came from a mixture of roughly 24,600 maize and 66,700 bean plants per hectare.
And yet the mixture won on land use, returning a 26 percent yield advantage over the mean sole crop yield of both species, with total income 32 percent above sole maize and 14 percent above sole beans in one season. The recommendation from that work is to hold the intercrop below 25,000 maize and 75,000 bean plants per hectare in seasons with ample rainfall.
Both facts are true at once. Your bean crop gets much smaller; your acre does more work. If beans are the crop you are counting on, as they are in Kabale, that trade looks different from how it looks to a maize grower.
Planting Depth, Gap Filling and the Germination Allowance
Depth is nearly settled. The Bean Cultivation Handbook specifies 5 cm, lightly covered; the NARO poster shows 4 cm. Treat 4 to 5 cm as the band. Deeper sowing delays emergence and weakens germination, and seed left at the surface may not pick up enough moisture to emerge at all, besides being easy for rodents to find.
Planting is faster in teams of three: one opening holes, one placing fertilizer and covering it with a thin layer of soil, one dropping seed and closing the hole. Then inspect the field three to four days after germination and fill gaps immediately, because a gap left open is a plant you paid for and will not harvest.
Gap filling only works if you kept seed back for it, which is the practical reason the germination allowance matters. Quality bean seed is specified at germination above 85 percent, purity 98 percent, non conformity under 2 percent, and dried to 13 percent moisture for planting use. A lot that meets those figures needs roughly 18 percent more seed than the bare plant count; a lot that does not meet them needs more than that, and you will not know which until the field emerges.
Planting Too Densely Buys You Disease
Chasing plant population has a cost that spacing tables rarely mention. The Bean Cultivation Handbook states it directly: a high population makes plants compete, leaves them weak, cuts yield, and creates a favourable environment and hiding place for bean pests and diseases. Too low a population simply wastes the land.
CIAT's bean disease handbook goes further and prescribes wide spacing as a control measure in its own right, for web blight, white mould, powdery mildew and Ascochyta leaf spot. The mechanism is air movement: a closed canopy holds free water on leaves for longer, and leaf wetness duration is what several of these pathogens need. Bean rust, for instance, needs more than ten hours of standing moisture on a leaf before it establishes.
So the densest spacing in the Ugandan literature, 30 cm rows at 10 cm, is not simply the highest yielding option. It is the option that also raises humidity inside the crop and shortens the interval before a leaf disease takes hold. On a wet highland site that trade is worth thinking about before you buy the extra seed. The pathogens involved are covered on our page on bean diseases and how Ugandan growers control them.
Checking Your Own Seed Rate Before You Buy
Weigh 100 seeds from the lot you plan to plant. That single measurement, plus the spacing you have already chosen, gives you a seed rate specific to your variety and your field, and it exposes the one figure a shop cannot argue with. If the rate you calculate differs sharply from the number on a poster, the seed size is usually the explanation, not an error.
Bean seed prices move with season and with seed class, and improved seed costs a multiple of grain. Before committing, it is worth checking current bean seed prices and comparing what is available near you. Seed classes and variety choice are handled in our bean seed selection guide, the plant population calculator and the seed rate calculator will run the arithmetic above for any spacing you type in, and the broader crop growing guides hub sets bean spacing alongside the rest of the season's work. For what those plants should return, see measured bean yield per acre in Uganda. Where to find certified and quality declared lots is covered under bean seed suppliers.
Questions Farmers Ask About Bean Spacing and Seed Rate Per Acre
Spacing and seed rate are the cheapest decisions in a bean crop to get right and among the most expensive to get wrong, because both errors are locked in on planting day. Weigh 100 seeds, pick your spacing, do the multiplication, and add the germination allowance before you buy. If you want the figures checked against what is available locally, compare current bean seed prices and ask an agricultural extension officer in your district which spacing the seed classes on sale near you were multiplied under.