The Secret To Growing Cauliflower From Seed

Cauliflowers are a wonderful crop to grow in the garden. Contrary to popular belief, growing cauliflower from seed is actually quite easy, if cared for correctly.

If you are worried about growing cauliflowers for the first time or have had problems in the past, you can make a few changes that will help grow large cauliflower heads.

In this article we will show you the secret to growing cauliflower from seed for harvest through summer and into late autumn.

Cauliflower Varieties To Try

different cauliflower varieties

Growing cauliflower from seed is complicated by the large seed companies, selling many different varieties for summer and autumn harvesting. 

There are also cauliflower varieties that can be harvested at different times. So you have spring, summer and winter and autumn varieties.

No guide about growing cauliflower from seed should leave out some advice on which varieties to grow.

So to help you get started, here are some cauliflower varieties you should try.

All Year Round: as the name suggests, this variety can be planted for harvesting all year, which makes it a popular choice. It’s a white variety, so you get a traditional white cauliflower head that tastes great.

Snowball: this is a summer blooming variety that will give you a high yield. You will get large, tasty snow-white heads.

Di Sicilia Violetto: originally from Italy, this cauliflower variety produces purple curds. You can harvest it in winter, so it will add a splash of colour to your garden at this rather grey time of year. When you cook it, it will turn green, and it is also very tasty.

Romanesco: this is another variety that originates from Italy and the curds have green spiral florets. It has a great taste too. You can harvest from mid-summer into winter. This variety is sometimes called broccoli, although it is a cauliflower.

That’s one of the great things about growing cauliflower from seed: you can get some weird and wonderful varieties.

Growing Cauliflower From Seed

cauliflower seedling

To get a good crop of cauliflowers it’s essential to sow cauliflower seeds indoors in trays or pots. From my trials, I have found that cauliflower plants grown in pots far outpreform those sown in a seedbed or straight outdoors.

Sowing indoors also gives you the chance to get crops earlier in the season. Use a good quality compost in 8cm (3in) plastic pots and plant two seeds per pot, pricking out the weakest plant after germination.

Sowing cauliflowers for early harvests begins in early February with late harvesting varieties planted before the last week in May.

But the seed packet will tell you when best to sow your chosen variety.

To get a good succession of cauliflowers, you can sow seeds regularly from February until the end of May.

The usual germination time for cauliflowers is 10-14 days.

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Planting Cauliflower Seedlings Outdoors

Cauliflower plants can be transplanted out once they have four or five true leaves. This is usually about 6 weeks after first sowing the seeds indoors.

Cauliflower plants are tough and can survive frost and bad weather fairly well. Planting a month to six weeks before the last frost date is fine.

In rich soil, I find a planting distance of  45cm (18in) apart in rows of the same spacing allows for good growth but prevents weeds from growing between the rows.

A good fertile soil is important for cauliflowers as they are very heavy feeders.

Adding a good amount of well-rotted manure or organic matter to the bed at least a month before planting outdoors is ideal as this adds organic matter, fertility and retains essential moisture.

If no rotted manure is available, then incorporating a blood, fish and bone fertiliser is a good alternative.

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You can also prepare your cauliflower bed by growing green manure and then dig it in to enrich the soil and improve the soil structure.

When planting outdoors, you can plant the seedlings below the current soil level. This will give the plant the extra stability that cauliflowers enjoy.

Firming the soil around the base of the stem with your heel gives the same effect. Cauliflower plants love firm soil.

Top Tip: make a hole, put the seedling in and fill the water with water. The water will close the hole with enough soil needed.

This will ensure the cauliflower plant has moist soil, which is what it requires. 

It’s worth mentioning that cauliflowers must be grown as part of a standard crop rotation. You cannot plant cauliflowers in an area that has grown other members of the brassica family (cabbages, broccoli, kale, sprouts) for the last two to three years.

Cauliflower Aftercare

When you have been growing cauliflower from seeds, you want to make sure that the seedlings do well. So here is how you care for your cauliflower plants.

Keeping the plants well watered and feeding regularly with seaweed feeds makes sure the cauliflowers grow quickly and remain of a very good quality.

In dry weather, you should water your cauliflower plants every 10 days.

Using mulch around the plant feeds the cauliflowers and keeps the soil moist, which is what cauliflowers crave so much.

Planting the plants just 45cm (18in) apart, blocks light to the weeds below. If you start with a clean bed, you should only need to weed the bed once about a month after transplanting the seedlings outdoors.

Harvesting Cauliflowers

Cauliflower head ready to harvest

Let’s get to the main reason we are growing cauliflower from seeds, harvest time.

It’s easy to tell when cauliflowers are ready. The heads will grow very quickly so checking regularly to see how they are growing will mean you don’t miss the first cauliflowers growing.

If you are growing multiple plants, begin harvesting when the cauliflower heads are still only 15-20 cm (6-8in) wide. Keep harvesting regularly as the heads quickly turn. Later in the season, the heads can be allowed to grow larger, but do not allow them to discolour as this means they are past their best.

Folding the leaves of the plant over the head of the cauliflower stops the sun discolouring the head and keeps them cool, which allows them to be kept on the plant longer without them spoiling.

If grown in succession, you should easily be able to harvest cauliflowers all year round.

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Diseases And Pests That Affect Cauliflower Plants

No guide about growing cauliflower from seed would be complete without a section about pests and diseases. 

Pests

Unfortunately, there are quite a few pests that might have their eye on your cauliflower.

The mealy cabbage aphid is one of them. It also attacks other plants from the cabbage family, such as cabbage, broccoli or kale.

severe infestation of cabbage aphids

Aphids are little insects that suck the sap from plants. They also secret honeydew, which is why ants like to “farm” them.

These aphids are grey/white and are found on plants of the brassica family. 

They are easy to spot, as they appear as a colony, so you will see a big cluster of them under the leaves of your cauliflower. 

You will also see leaves turning a pale yellow where the aphids have been feeding.

Well established plants can cope with an aphid colony feeding on them, but they can kill young plants.

There are things you can do to get rid of aphids:

  • do tolerate them where possible, as they are prey for many other insects.
  • if you are not squeamish, you can remove them by hand
  • Or, if the plant is strong enough, you can put newspaper on the ground and carefully shake the plant, the aphids will drop off, and you can move them to a par to of the garden where they won’t do much harm
  • You can also try companion planting. With this gardening method, you plant different plants together for a mutual benefit. So you could plant chives with your cauliflowers, because they will repel aphids with their scent.
  • You can wash your plants with insecticidal soap too, but unless your plant is in grave danger of not surviving the attack, such a move should not be necessary.
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Another pest that will attack cauliflowers is the cabbage root fly

This fly looks very much like a housefly. The females will lay their eggs in the soil under your cauliflower and their larvae, white maggots with no head or legs, will then eat the roots.

This can cause a stunt in growth in your cauliflower plants, and they could even wilt and die, because without roots they can’t feed.

Because they operate underground, it is difficult to spot them before they are a problem. And it’s so disheartening, when you are growing cauliflower from seed and a pesky pest destroys all your cop.

So you want to prevent the flies from laying their eggs near your plants. And here are preventative measures you can take:

  •  You can cover your cauliflower plants with insect-proof netting.
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  • You could put brassica collars around your cauliflower plants. These cover the soil around the plant, preventing the flies from laying their eggs there.
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  • You could also try companion planting. Thyme is said to repel the cabbage root fly. So planting this herb close to your cauliflower will keep them pest free.
  • Encouraging natural predators of this pest can help, such as the rove or ground beetles. A pile of logs or a compost heap will attract them to your garden.
  • You should also practise crop rotation, as they can overwinter in the soil. 

Other larvae that like to feed on brassica are cabbage caterpillars. They are the larvae of the cabbage moth, diamond-back moth and the cabbage white butterfly (actually there are two, the small and the large white butterfly).

Of these species, the cabbage moth and small white cabbage butterfly caterpillar cause the most damage, as they borrow into the developing cauliflower heads. 

The large white cabbage butterfly and diamond-back caterpillar feed on the leaves.

You can distinguish the various species by looking at the caterpillars:

  • Large white cabbage butterfly: yellow and black and hairy body
  • Small white cabbage butterfly: pale green with short hair
  • Cabbage moth: yellow-green or brown-green, hairless
  • Diamond-back moth: green and quite big (1cm/0.39in)

It’s easy to see if you have caterpillars munching on your plants, as they will leave wholes everywhere. And if you have a close look, you can also see them, although some are quite well camouflaged.  

Here is what you can do to prevent the caterpillars from spoiling your crops:

  • Covering your cauliflower with insect-proof netting, but make sure the mesh does not touch the plants, otherwise the moths and butterflies can still lay their eggs
  • attract natural predators, such as wasps and birds, by planting plants such as marigold, Yarrow or dill.
  • You can also pick off any caterpillars or eggs you see
  • You can plant onions, garlic, marigold, lavender, thyme or oregano with your cauliflower plants to put off the moths and butterflies from laying their eggs

Pigeons also love brassica seedlings. We once had all our 20 broccoli seedlings eaten by a pair of pigeons in a day.

pigeon on garden fence

So you need to protect your cauliflower seedlings from these hungry pigeons. You can do that by covering them with bird netting.

Or cover them with halved plastic bottles, squash bottles work well. Just put the top half over the seedling, and they will be safe.

Diseases

When you put all this effort in growing cauliflower from seed, you don’t want to lose your coops through diseases.

One disease that could infect your cauliflower is club root. It’s caused by a fungus that affects the roots of plants of the cabbage family.

It’s a soil-borne disease that will cause the roots of your cauliflower to become swollen and distorted. This will slow down and stunt the growth of the infected plants.

The fungus thrives in warm and moist conditions, so the risk is biggest from mid-summer to late autumn.

Signs you will see on your plants are slower growth and the leaves starting to wilt and turn a purple colour in hot weather conditions. 

If it gets colder again, the plants might seem to get their health back, but this will only be temporarily.

If you pull up the plants you will see that the roots are swollen and deformed, the thinner roots might be missing altogether.

Because this diseases affects the roots, the plant has difficulties to get the nutrients it needs, which means it won’t be able to produce as many or as big a crop. So your yield will be diminished by quite a bit.

Very heavy infections can kill the plants.

Once a plant is infected, there is no cure, so prevention is the only way forward. Here are preventative measures you can take:

  • When growing cauliflower from seed, make sure you buy your seeds from a reputable supplier that guarantees that the seed are diseases free. If you want to buy plants instead, again, make sure they are free of club root. 
  • If you are aware that you have club root in the soil, keep your seedlings longer before you transplant them. This will give the seedling a chance to develop a stronger and bigger root system, which will be more resistant to the disease. Just use a bigger pot, 10cm (4in) at least, to prevent the plants from becoming root bound.  
  • Always clean tools and boots you used when working in an infected bed, to avoid spreading the disease to a non-infected area.
  • Good drainage will will also minimise the risk of an infection taking place
  • Weed your beds regularly to prevent the disease being introduced by a weed.
  • There are also varieties that are resistant to club root, and it might be worth giving them a try. Clapton F1 and Clarify F1 are such varieties.
  • Club root is more prevalent in acid soils, so you can raise the pH level of the soil by adding lime to it.

If you don’t know the pH level of your soil, you can get a DIY home soil testing kit.

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If you do have acid soils, you can add lime to raise the pH level.

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Another diseases is brassica downey mildew, which is caused by an organism that is like a fungus.

It loves wet conditions, so it can attack from spring. At that time of year it will affect seedlings, but in summer and early autumn it can also attack mature plants.

The signs to look out for is a layer of white mould on seedlings, which will kill them. On mature plants you will see yellow spots on the top of the leaves and white mould on the bottom. The leaves will dry out and die eventually.

If you open the cauliflower curds, you will see that they are brown inside.

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Once the organism has infected the plant, there is nothing you can do.

So to save yourself from this disheartening feeling of seeing your efforts ruined after growing cauliflower from seed, you can take these measures to minimise the risk of an infection occurring.

  • Practice crop rotation, to avoid a build up of the disease
  • Plant your plants far enough away from each other to allow for good air circulation. The air flow will keep the foliage drier and thereby preventing favourable conditions for the disease
  • Make sure you weed the beds regularly to reduce the risk of them getting infected and passing it on
  • If you spot any signs of an infection with brassica downey mildew, remove the infected plant and destroy it immediately

With brassica downey mildew another disease could strike a the same time, brassica white blister

Because they favour the same conditions, they often occur at the same time.

White blister is a foliar disease caused by a fungus-like organism. 

You will see very light spots on the underside of the leaves, which will turn into blisters, hence the name. These will eventually release the spores.

Around the blisters or spots you will also a discolouration. 

While the leaves are the first to be get infected, the disease will spread to the stems, flowers and seed pods.

The disease will also cause the whole plant to become distorted. I will just not look right anymore.

As a result, the plants health will suffer and the affected parts will die.

To prevent an infection, take the same measures as described above for the downey mildew.

Now that you have read our guide about growing cauliflower from seed, you are ready to try it out for yourself. Happy Growing!

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