How do you get big broccoli heads?

QUESTION: I tried growing broccoli last year, but the broccoli heads were small and it wasn’t really worth growing. How do you get big broccoli heads? -John L

ANSWER: There are several things that you can do to help improve the size of your broccoli heads. First and foremost, fertilization is essential. Before planting, work into your soil plenty of rotten manure and some blood meal or cottonseed meal to boost your soil with lots of essential nutrients that your broccoli plants can feed off of. Every three to four weeks, when watering your broccoli plants, water using an organic fertilizer or fish emulsion. Feel free to do some research and pick out different fertilizers that you think will give you the best advantage, but no matter what, fertilize your plants early and often. The most important thing you can do to help cultivate big broccoli heads is to feed your plants.

Another key factor in growing big broccoli heads is making sure that your broccoli plants get plenty of water. Rainwater is preferable, but it is not always sufficient. With or without the rain, make sure that your broccoli is getting one to one and a half inches of water each week. Missing a few waterings will have noticeable effects on the size of your broccoli plants, so be sure to give them a steady and healthy amount of water and don’t just rely on the rain to handle your irrigation for you.

Another method that you can implore to help boost the size of your broccoli heads is to lay out two to three inches of organic mulch, such as finely ground straw or grass clippings. A nice, thick layer of organic mulch will help to keep the soil from overheating which is important because excessive heat levels will cause broccoli to bolt early. To get the largest broccoli crowns, you need to allow your broccoli the most amount of time possible to mature without allowing the crowns to flower prematurely. Mulching can go a long way towards achieving this balance.

However, in cool climate areas with lots of moisture, mulching your broccoli plants is probably not a great idea, as it promotes increased water retention. Waterlogged soil can lead to a slug problem. So, if you live in a cool climate area and you get lots of rain, you might want to lay down eggshells and skip the mulch to promote better drainage, letting the eggshells do their job in deterring slugs.

Another way to give your broccoli plants a boost in size is to add in some extra boron to your soil. Broccoli, as well as other cole crops like cabbage, cauliflower, kale, and kohlrabi, all benefit from significant amounts of boron in the soil. If your soil leans heavily to either side of the pH scale, the boron in the soil will be harder for your plants to absorb. If you notice the new leaves of your broccoli plant beginning to yellow or catch the growing tips beginning to wither, this is likely the first sign of boron deficiency. To give your broccoli plants a boost of boron, add ¼ cup of boric acid to two gallons of water and use it as a foliar spray. Be sure to get the dilution levels correct, as heavy doses of boron can be toxic to plants if not properly diluted.

Take your time to research and select the right variety of broccoli for your area. There is a wide variety of broccoli types available for gardeners and they all come with different growth habits and production preferences. Some of these are known to grow larger heads than others too, so be sure to pick a variety that is suited to your area and known for producing large heads. Some of the broccoli varieties that are recommended for large heads include Belstar, Arcadia, Green Goliath, Superdome, Green Magic, Everest, Packman, Galleon, Early Dividend, Blue Wind, and Southern Comet. 

Lastly, a 1997 study published in, “The Kasetsart Journal” found that pinching off all of the broccoli plant’s lateral or side shoots as they develop during the growing season leads to the development of a larger main head. So, if you don’t mind sacrificing the broccoli greens for a larger head, pruning the side growth can also lead to bigger broccoli heads.