One of the most important factors in the size of your broccoli heads is timing. Broccoli likes to be kept cool. Broccoli plants that are planted too late in the spring may start buttoning when the weather becomes too hot for their liking. Buttoning will cause the plant to produce tiny broccoli heads.
There are several things that you can do to help improve the size of your broccoli heads. First and foremost, fertilization is the most important contributing factor. Before planting, work plenty of rotten manure into your soil and some blood meal or cottonseed meal to boost your soil’s essential nutrient levels which your broccoli plants feed off of.
Every three to four weeks, when watering your broccoli plants, water use 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, don’t skip fertilizing your plants early and often. The most important thing you can do to help cultivate big broccoli heads is to feed them sufficiently.
Another key factor in growing big broccoli crowns is providing plenty of water. Rainwater is preferable, but it is not always enough. With or without the rain, make sure that your broccoli is getting at least 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 rely on the rain to handle all irrigation needs for you.
Another method that you can use to help increase the size of your broccoli heads is to lay out two to three inches of organic mulch around your broccoli plants, such as finely ground straw or grass clippings.
A nice, thick layer of organic mulch will help to keep the soil cool, 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 from overheating. Mulching can go a long way towards making this happen.
In cool climate areas with lots of moisture,you might want to lay down eggshells and skip the mulch to promote better drainage, letting the eggshells do their job in deterring slugs, which become an issue in waterlogged soil.
Other ways to improve your broccoli head sizes is to add boron to the soil or treat the plants with diluted boric acid in a foliar spray, selecting the right variety of broccoli for your climate area and for producing large crowns, and pinching all lateral or side shoots so that the plant focuses on making a larger broccoli head instead.