7 Broccoli Growing Mistakes to Avoid This Season

Growing broccoli doesn't have to be difficult, but there are some important factors to consider if you want a bumper crop of this green veggie. Gardening expert Melissa Strauss has some mistakes to avoid when growing your own cruciferous crop.

Tight green cluster of unopened flower buds forming a dense head atop thick pale green stems.

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I’m not sure how it happened, but broccoli is always a hit on my dinner table. Even my four-year-old is happy to hear that this tasty and healthy vegetable is on the menu. Growing it in my own zone 9 garden isn’t always as easy as getting these kiddos to eat it, though. 

Broccoli is a cool-weather cruciferous vegetable. It prefers the mild temperatures of spring and fall, so in places where the spring heats up quickly, it can be a challenge to grow. It needs a lot of sun, but the afternoon exposure can get too intense early in the season. Fortunately, for cool-climate gardeners, there are fewer hurdles to overcome. 

No matter where you grow it, there are some important factors to growing a healthy, booming crop. Let’s take a look at some potential mistakes we can make and how to grow the perfect heads in your garden. 

Mistake 1: Starting Too Late

Young green seedlings with broad oval leaves and thick pale stems growing in dark soil inside a black grow bag.
In warm zones, plant this in fall for winter harvests; it sweetens after a light frost.

Because broccoli prefers to grow in cooler temperatures, it’s an easy mistake to miss the ideal planting window. This is especially true for warm-climate gardeners. If you don’t start those seeds on time, you can run into a couple of issues. 

Depending on your zone, you can grow this crop in spring or fall. In warmer climates, you may find that fall sowing for a winter harvest is more conducive to the overall success of your crop. It’s a frost-resistant vegetable that actually gets tastier after a frost or two. It’s like many leafy greens in this regard. 

Because broccoli needs cool temperatures to germinate, starting it in the late summer and early fall can be challenging. This mistake is much easier to avoid in cooler climates, as the growing season for broccoli is longer here. 

Solution

You can directly sow seeds in the garden as soon as the ground is workable. However, the seeds are small and tend to do better if you start them indoors. In warm climates, you can start them about six weeks before transplanting. Since they are frost tolerant, this may be as early as December.

In cool climates, plan to move them outdoors as soon as the ground is workable or about four to six weeks ahead of your last frost date. Start them roughly six weeks ahead of transplanting. Place them in a cool location and forgo the seed heating mat for these. They germinate well at about 60°F (16°C).

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Mistake 2: Crowding Your Plants

Several dense green flower bud clusters on thick pale stems surrounded by large gray-green leaves with wavy edges.
Give seedlings enough space, or they’ll grow weak, spindly, and develop shallow roots competing for nutrients.

Give your seedlings a space of their own when you start them. If you sow too many seeds in one cell, your baby plants can grow leggy and tall, which is something you don’t want. These will be weak and spindly and won’t have great root development because they share that small space. 

Solution

Only sow a maximum of two seeds per cell or space in the bed. Since they are small, it’s easy to overdo it unintentionally. This isn’t the end of the world, but as I mentioned, it can land you with spindly plants. If you accidentally spill too many in one spot, just thin them out early. Broccoli sprouts are tasty and nutritious, so go ahead and toss those extra sprouts on your salad or sandwich!

Mistake 3: Waiting Too Long to Transplant

Gloved hands planting green seedlings with thick stems and broad leaves into dark brown garden soil.
These plants need cool weather for strong growth; avoid planting in consistently warm seventy-degree temperatures.

Another common mistake is waiting too long to get your transplants into the ground. This creates two issues. The first is the strength of your plants. If you leave them in a small cell for too long, they won’t have space to grow strong roots. They will instead grow tall and spindly, which makes for weaker broccoli. 

The second issue is their need for cool weather to do the bulk of their growth. It’s better to expose them to frost than to wait until you’re consistently experiencing temperatures in the 70s (~21°C). If you don’t give your young plants ample cool weather to put on growth, you may end up with weak broccoli. 

Solution

Start your seeds in a timely manner, accounting for your climate. Give your young plants a week or two to harden off before you move them outdoors permanently. This combination will give you strong, sturdy starts that grow into strong, healthy veggies.

Mistake 4: Planting in the Wrong Spot

Gloved hand placing a single green seedling with pale thick stem into loose brown soil.
Choose a spot with sun, rich soil, good drainage, and water for healthy, productive plants.

Choosing the right location is paramount to success in growing any vegetable or plant, for that matter. If they don’t get the right amount of sunlight, the right type of soil, the right amount of water, and proper drainage, you’re not going to get the best performance. Broccoli is no exception to this. 

Solution

Broccoli needs a lot of sun exposure, at least six hours per day, to thrive. In warmer climates, it’s best to give them afternoon shade to extend the season. Afternoon exposure is hotter and more intense and will shorten the life of your plants.

For the best results, bulk up your soil with plenty of organic material. This is a heavy feeder, so if it doesn’t get adequate nutrients, it won’t perform nearly as well. Make sure your soil drains well and has a slightly acidic to neutral pH.

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Mistake 5: Neglecting to Fertilize

Hand holding small blue trowel spreading dark compost around green plants with broad leaves and thick stems.
Heavy feeders need steady nutrients, or they’ll languish and produce disappointing, lower-quality yields at harvest.

As I mentioned above, broccoli is a heavy feeder, and it is a mistake to leave it without sufficient nutrients. It requires a strong and steady supply of specific nutrients to perform and produce. If they don’t get what they need, you can expect your plants to languish and produce a sub-par harvest.

Solution

Start out with a formula high in phosphorus for healthy root development. About a month after transplanting, give your plants a dose of nitrogen-heavy fertilizer. This will help them produce plenty of robust, green growth.

After that first application, you should fertilize about once every two to three weeks. You can back off of the nitrogen slightly at this point, but don’t eliminate it altogether. Use either a balanced formula or one that is slightly higher in potassium and phosphorus, such as a 5-10-10 ratio.

Mistake 6: Planting With The Wrong Neighbors

Bushy plants with dark green, fern-like leaves feature clusters of bright, round orange and yellow blooms with layered petals.
Marigolds are great companions because they don’t compete for nutrients and support healthy plant growth.

Another issue with heavy feeders is that they make complicated neighbors. If you plant them too close to other plants that need a substantial amount of nutrients, they will compete, and neither will thrive as it should. You could end up with a lousy yield from both, which is always disappointing. 

Solution

Choose the right companions for your broccoli based on the needs of both or all plants involved. Avoid other heavy feeders like tomatoes, potatoes, and other brassicas. Instead, opt for neighbors that don’t need as many nutrients. Marigolds make great neighbors, as do most herbs.

Mistake 7: Ignoring Pests

A close-up of several small, green cabbage worms feeding on a large Brassica oleracea leaf, the damaged areas of the leaf showing clear holes and discoloration against the healthy green surface.
Pests like cabbageworms, webworms, flea beetles, and maggots target these plants and can quickly destroy crops.

As much as we like to eat this vegetable, there certainly are a lot of pests that also like to dine on its leaves and flowers. It is a big mistake to leave your broccoli unprotected. Aphids, of course, are a common garden nuisance that may come after your broccoli. Armyworm and cabbage looper larvae will defoliate a plant quickly. 

Because it is in the same family as cabbage, all the usual cabbage pests apply. Cabbageworms, webworms, and root maggots are all concerns. Flea beetles can be a major issue, too. Overall, there are a host of insects that can affect your plants, and they can ruin your crop in short order. 

Solution

Be vigilant. Regularly monitor your broccoli for signs of pests and diseases. Some pests, like various caterpillars, are easy to eradicate with physical control. You can pick them off by hand and eliminate most of the problem.

Smaller pests like aphids and flea beetles are more complicated. Covering your plants with row covers is a good way to protect them from damaging infestation. Larger specimens are less vulnerable, but a heavy infestation can damage the strongest of them. Neem oil and Bt are good treatments for getting rid of these, and they’re safe for humans and pets.

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Close-up of a gardener's hand harvesting broccoli, revealing dark blue-green leaves with prominent veins fanning out around a dense, central cluster of tightly packed green buds.

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