How to Grow Broccoli from Seed
As an Amazon Associate we earn from qualifying purchases.
How to grow broccoli from seed comes down to three decisions: when to start, how deep to sow, and how far apart to space the plants. Broccoli is a cool-season crop, so the calendar matters as much as the seed. The university guides below agree on the basics. They differ on some numbers, so this guide shows each figure with its source and names the gaps. Nothing here recommends a product.
Quick answer
- Sow seed one-quarter to one-half inch deep, then thin to the final spacing once the seedlings have three or four true leaves.
- If you grow transplants, sow indoors about six to seven weeks before the planting date.
- Plant out two to three weeks before the last spring frost date, a range that both the Penn State and Utah State guides give.
- Space plants 12 to 18 inches apart in rows 2 to 3 feet apart, and give them about one to two inches of water a week.
Timing starts with the last frost date
Broccoli can be grown in spring and in fall, and the start date is the first decision. The Penn State PlantVillage page says “Spring plantings should be made 2-3 weeks before the last frost date”, meaning the date for your own area, and it puts fall plantings about 100 days before the first fall frost. Late-spring plantings can run into summer heat. The Utah State guide warns that high summer temperatures cause loose heads to form, which taste bitter.
The Texas A&M extension guide ties spring sowing to soil temperature as well as to the calendar. Its table lists a soil seed-zone temperature above 40°F for spring planting and gives a seeding depth of one-quarter inch. The same table lists 65 to 100 days from direct seeding to harvest and 50 to 70 days from transplanting. Those ranges are useful, but the table does not tie them to a sowing date, so check any calendar against your own frost dates.
Heat sets the upper limit. The NC State page is about sprouting broccoli, a related type, and it says “Higher temperatures lead to poor head formation”. The same page says growth slows below 41°F. Read the NC State figures as guidance for a related crop, not as a rule for heading broccoli.
Start seed indoors for transplants
Indoor starts give you a head start on the season. The Utah State guide says “Broccoli grown for transplants should be sown 6-7 weeks before the expected planting date.” Seed sown directly can go out at the same time as transplants, according to the same page.
The Penn State page recommends peat pots when you start seed indoors, since the pots help you avoid root disturbance at transplanting. It says seedlings can go outdoors at three to four weeks old. Set each transplant a little deeper than it sat in its pot. The page puts it this way: “Plant transplants slightly deeper in the ground than they currently are in their pot”.
Transplant quality matters as much as the date. The Utah State guide says “Transplants should have 4-6 mature leaves and a well-developed root system before planting out.” Larger transplants are more likely to button, which the same guide describes as “prone to form small, early heads (buttoning)”. Choosing plants with four to six leaves is the simplest way to avoid that problem.
Sow and thin in the garden
Sowing depth is shallow for broccoli. The Utah State guide says “Seeds should be planted ¼-½ inch deep” and thinned once the plants have three or four true leaves. Penn State’s page is close to that: it says to “Sow seed 1.3 cm (0.5 in) deep in small groups of 2-3 seeds” and to thin about a week after emergence. Sowing in small groups gives you a spare seed in case one fails, and thinning reduces each group to a single plant.
The spacing figures differ, so the table below sets them side by side. Each cell is the figure the page states. Where a page gives no figure, the cell says not stated.
| Source | Sowing depth | Spacing in the row | Spacing between rows |
|---|---|---|---|
| Penn State (PlantVillage) | 0.5 in (1.3 cm) | 12 to 24 in (30 to 60 cm) | 36 in (90 cm) |
| Utah State | ¼ to ½ in | 12 to 18 in | 2 to 3 ft |
| Washington State (WSU) | not stated | 12 to 24 in | not stated |
Treat the table as a range, not a rule. The Utah State guide notes that closer spacing, such as one foot by one foot, can be used, but “head size is reduced and side shoot development inhibited”. A closer planting gives you more plants in less space, at the cost of the larger heads that wider spacing allows.
Choose the bed and the soil
The Penn State page describes “moist, fertile soil” for broccoli and notes that the crop has a high nitrogen requirement. Organic matter should go into the bed through the year, so nutrients are ready when the plants go out. The Utah State guide adds that a soil test should come before any fertilizer is applied, since the test report sets the rate.
For bed-building basics, see how to fill a raised bed. For other crops that share a bed with broccoli, see vegetables to plant in raised beds. Both posts cover the bed itself, so the spacing and feeding advice in this guide still applies once the bed is ready.
How many plants fit a 10-foot row
The spacing ranges turn into plant counts quickly. A 10-foot row is 120 inches long. Spaced 12 inches apart, the lower end of Penn State’s range, the row takes about 10 plants. At 18 inches apart, the upper figure in the Utah State guide, it takes about seven. At 24 inches apart, the top of Penn State’s range, it takes about five. These counts are arithmetic from the spacing figures, not numbers that any of the pages gives.
Row spacing sets how many rows a bed can hold. The 36-inch figure from Penn State and the two to three foot range from Utah State both point to wide rows, so plan the bed from the spacing you choose and check the plant count against the bed size before you sow.
Water, mulch and feeding
Water comes next. The Utah State guide says “About 1-2 inches of water are required per week.” The NC State page gives a similar range of one to one and a half inches a week, and it says the figure depends on location, cultivar, production system and soil type. NC State also notes that drip irrigation is efficient, while overhead watering can raise disease pressure.
Keep the soil around the plants undisturbed. The Penn State page says “Broccoli has a very shallow root system”, which is why cultivating close to the stems can damage the roots. Mulch helps with both moisture and soil temperature. The same page says “Mulching around the plants helps to conserve soil moisture and reduces the soil temperature.” Pulling weeds by hand near the plants fits that advice better than hoeing close to the stems.
For feeding, the Utah State guide suggests a light nitrogen application about four weeks after transplanting or thinning. A second, small dose goes on when the head is about the size of a quarter. Place the fertilizer about six inches to the side of the plants and water it into the soil. The guide says to work fertilizer into the top six inches of soil when a soil test calls for it.
Protect seedlings from cold and heat
Cover young plants when frost threatens. The Utah State guide says “Hot caps and fabric covers are used to protect seedlings and transplants from frosts.” Fabric covers also protect young plants from insect pests, according to the same page, which lists small black beetles that chew holes in seedling leaves.
Heat is the risk in the other direction. The Utah State guide says “Broccoli grows best and produces highest yields when temperatures do not exceed 75°F”, and it adds that a healthy plant is not seriously damaged down to 28°F. The same guide recommends organic mulch once temperatures rise above 80°F, because straw and shredded newspaper help cool the soil.
Harvest and side shoots
Harvest by the head, not the calendar. The Penn State page says “Broccoli is ready to harvest when the flower buds are firm”. Cut the stalk before the buds open, at a 45-degree angle about 5 to 8 inches below the head. The Utah State guide puts a mature head at “6-12 inches in diameter” and says side shoots keep producing after the first cut.
Side shoots are the second harvest. The Utah State guide says that with extra water and fertilizer, the plant produces many side shoots of 3 to 6 inches long. Keep watering steady through that second phase, since the guide ties water and nutrients to side-shoot growth.
Pests and diseases
Several of these guides list seedling problems. The Penn State and Utah State pages both list damping-off of seedlings, and the Utah State page also lists the small black beetles mentioned above. This guide does not give treatment advice for either. For any control decision, read the label of the product you plan to use and check with your local extension office.
A rough indoor-start window from the frost date
Two figures from the guides can be combined. The Utah State guide says transplants can go out two to three weeks before the last frost-free date, and it says to sow transplants six to seven weeks before planting. Adding those together gives a window of about eight to ten weeks before the last spring frost. This is arithmetic from the two figures, not a date that either page gives. For a last frost on May 1, the window runs from about February 20 to March 6.
What we could not verify
The sources give ranges, and the ranges do not always agree. The Penn State page gives 12 to 24 inches between plants, while the Utah State guide gives 12 to 18 inches. Neither page gives one figure that fits every climate, so check your own frost dates and the days-to-maturity notes on your seed packet.
What the sources do not say
The pages reviewed here do not give a days-to-harvest figure for seed started at home. The Texas A&M table gives 65 to 100 days from direct seeding and 50 to 70 days from transplanting, but it does not connect those numbers to a sowing date. The Utah State guide lists days to maturity for several named varieties, which this guide does not repeat, since it names no products. The NC State figures apply to sprouting broccoli, so they are a close guide, not an exact one, for heading types.
How we chose
The guide relies on university extension pages, including one from Washington State, all opened with curl on 2026-10-23 and all returning HTTP 200. It uses only what those pages state, and each number carries its source. It does not name seed varieties, brands or product types, and it does not treat any retail listing as a source. Where two sources disagree on a number, the guide shows both figures instead of choosing one silently.
Frequently asked questions
Can you sow broccoli seed directly in the garden?
Yes. The Penn State page says “Broccoli can be direct seeded or started indoors for transplants.” Direct sowing uses the same depth and spacing ranges shown above, and the Utah State guide notes that seeded broccoli can be planted at the same time as transplants.
How deep should broccoli seed go?
The Utah State guide gives one-quarter to one-half inch, and the Penn State page gives about half an inch. Both place the seed shallow. The table above shows how the two figures line up with the other sources.
How far apart should broccoli plants be?
Penn State gives 12 to 24 inches within the row and 36 inches between rows. Utah State gives 12 to 18 inches in the row and 2 to 3 feet between rows. A tighter layout, such as one foot by one foot, is possible, but the Utah State guide warns that it reduces head size.
Why did my broccoli form small heads so early?
The Utah State guide calls this buttoning, the early formation of small flower heads. It links buttoning to cold weather, or to water or nutrient stress before or after transplanting. Pick transplants with four to six leaves and keep the soil evenly moist to lower the risk.
How much water does broccoli need each week?
The Utah State guide says about one to two inches. The NC State page says one to one and a half inches, with the figure depending on location, cultivar, production system and soil type. Use the lower end of each range in cool, moist weather and check the soil rather than the calendar.
Sources
- https://plantvillage.psu.edu/topics/broccoli/infos (opened 2026-10-23)
- https://aggie-horticulture.tamu.edu/vegetable/files/2011/10/broccoli.pdf (opened 2026-10-23)
- https://extension.usu.edu/yardandgarden/research/broccoli-in-the-garden.php (opened 2026-10-23)
- https://content.ces.ncsu.edu/basics-of-broccoli-production (opened 2026-10-23)
- https://wpcdn.web.wsu.edu/wp-snaped/uploads/sites/2/2022/06/How-To-Grow-Broccoli_WSU_E.pdf (opened 2026-10-23)
