HOW TO GROW PURPLE SPROUTING BROCCOLI
Purple Sprouting Broccoli is traditionally grown in the UK with the aim of producing a crop in the “lean” months of November to March.
Some new varieties can now be harvested from late July to late October. However the harvest quality of these new early varieties has yet to match traditional Purple Sprouting Broccoli.
Extremes of weather (excess rain and / or above average temperatures) and pests (pigeons and caterpillars) are the key enemy for a successful broccoli crop. With exception of excess rain, those enemies of broccoli can be managed with careful planning.
This article is about growing purple sprouting broccoli, not calabrese. There is often confusion about the naming of these two vegetables. Purple sprouting broccoli (typically purple but can be white) is normally grown to produce a crop starting in winter and lasting until early spring. It is a cut and come again crop so its cropping season is long.
Calabrese (often wrongly called broccoli) produce a crop in late summer only and typically consists of only a few large green heads. See the two pictures below to distinguish between the two. The cultivation methods of sprouting broccoli and calabrese are very different as are the edible crops.
Above is Sprouting Broccoli (purple)
THIS ARTICLE IS ABOUT SPROUTING BROCCOLI
Above is Calabrese
THIS ARTICLE IS NOT ABOUT CALABRESE
Purple Sprouting Broccoli can be sown in a seed bed and then transplanted to its final position. It can also be sown under cover in seed modules and then transplanted to its final position. We recommend sowing under cover although the timings for both methods are given below.
There are early season to late season varieties of purple sprouting broccoli. If both are sown then this will extend the cropping season. The calendar below gives timings for both early (shown in blue) and late varieties (shown in green). Identify which variety is which by reading the seed packet.
CALENDAR FOR GROWING PURPLE SPROUTING BROCCOLI
Sow early varieties under cover – second week of April
Sow late varieties under cover - fourth week of April
Sow early varieties in seed bed - third week of April
Sow late varieties in seed bed - first week of May
Plant early varieties (sown under cover) into final position - first week of July
Plant early varieties (from seed bed) into final position - second week of July
Plant late varieties (sown under cover) into final position - second week of July
Plant late varieties (from seed bed) into final position - third week of July
Start harvesting early varieties - second week of February
Start harvesting late varieties - fourth week of February
All purple sprouting broccoli takes up lots of room, at maturity the plants are large. In order to make the best use of your garden / allotment space they will normally be sown initially in small pots / modules or in a seed bed. Only when the plants are about 12cm / 5in tall will they be planted into their final position.
Prior to planting in their final position, the ground can be used for other quick maturing crops such as lettuce and radish.
Consider carefully how many plants are required, there is little point in growing a large number of plants if the crop is too large for you to harvest. For two adults and two children, five or six plants is all that is required for a plentiful crop.
SOWING PURPLE SPROUTING BROCCOLI IN MODULES / POTS
If you are growing less than ten plants then we would recommend sowing the seeds in small (7cm / 3in) pots. They can stay in these pots until they are ready for transplanting to their final positions. Alternatively, sow the seeds in modular seedling trays which are about 2cm / 1in wide.
Sow early varieties of purple sprouting broccoli in third week of April and sow late varieties in fourth week of April . There is little to be gained by sowing earlier than this date (use our free date adjustment feature to get the timing exactly correct for your area). In fact sowing the seeds too early will result in much larger plants which are then more liable to frost and wind damage.
To do this fill the pots / modules with well sifted (i.e. all the lumps removed) potting compost. Multi-purpose compost can also be used but you will need to remove or crush many more lumps in the compost. Fill the pots / modules to the top with compost and sharply tap them on a flat surface two or three times to settle the compost slightly.
Make small holes in the compost about 1.5cm / 0.75in deep (you can use your small finger to do this) and sow two seeds per hole. Cover each hole with compost without firming down the compost.
Water the pots modules / trays. Without a doubt we find the best method for this is to fill a container with about 2cm / 1in of water and place the pots / modules in that for 5 minutes or so. Take the pots / modules out and allow them to drain for 10 minutes or so.
If you water from above using a watering can, this may well disturb the seeds and / or result in the top being waterlogged but the base not fully watered.
Place a marker in the pots / modules to identify the variety and date sown.
Although purple sprouting broccoli can withstand very low temperatures when established, the seeds germinate best and quickest when the soil temperature is in the range 21C to 27C (70F to 80F).
The seeds will germinate in total darkness if you want, but immediately they germinate and you see green shoots they should be transferred to a position with lots of light.
When the seeds have germinated they require lower temperatures to grow on than for germination. The best place to grow the seedling on is a coldframe / greenhouse or a a cool but light windowsill. Keep the coldframe / greenhouse well ventilated on warm days. Coldframes / greenhouses may well need some heat (or temporarily bring the plants indoors) if the temperature drops below 10C / 50F.
If growing them on a windowsill, the plants can be placed outside after a week or so in a light and well protected position as long as temperatures don't drop much below 10C / 50F. If the temperature does drop, bring them inside until it rises again.
You will have sown two seeds per pot / module, if both come up then pinch out the weakest with your fingernail.
If you have sown the seeds in modules, they should be transplanted to small pots (7cm / 3in) after about four weeks.
Almost all good quality potting composts (and general purpose multi-purpose composts) have sufficient nutrients built in for the first four weeks after sowing the seeds or transplanting.
SOWING PURPLE SPROUTING BROCCOLI IN SEED BEDS
The purpose of sowing purple sprouting broccoli in a seed be is to conserve space and allow you to grow more quick maturing crops in the area the broccoli will finally occupy.
The key advantages of sowing in seed beds is that the seeds will germinate when the ground is warm enough to support germination. The seedlings will tend to be more cold weather resistant compared to growing them under cover.
The disadvantages are that as soon as the seedlings emerge they may well be attacked by pests. Pigeons and other birds can pull up a whole bed of broccoli seedlings in a day. Slugs and snails can decimate them in almost the same time frame.
My own personal experience is that sowing purple sprouting broccoli in a seed bed is a recipe for disaster!
As far a sunshine goes, purple sprouting broccoli does best in full sun although it will easily tolerate light shade. Most varieties are tall growing plants which prefer a position protected from strong winds. If this is not possible, the plants should be individually staked.
As far as soil goes, purple sprouting broccoli prefers a neutral to alkaline soil. If you have acidic soil it is possible to add lime to make it more alkaline, however, it will be an uphill battle.
Heavy soils, light clay to heavy clay is ideal, help to anchor the plants down and also retain moisture, so vital to the success of this vegetable plant. Light soil can be improved by the addition of well rotted organic matter such as compost.
Similar to sweetcorn, purple sprouting broccoli thrive on a water retaining soil. Even though our soil is moderately heavy clay we mulch the soil heavily for both sweetcorn and broccoli. This reduces the need for hand watering very considerably in even almost drought conditions.
Our method, soon after the plants are planted in their final final position, is to line the soil all around and in between the plants with cardboard. This is readily available for free near the exit at almost all large supermarkets and hardware stores.
Over the cardboard place lots of mulch - we use woodchip because it is readily available to us. However, grass clippings continually applied as you cut your grass is as good. Weeds in the grass cuttings will find it difficult to establish because of the initial layer of cardboard.
Pile whatever mulch have onto the cardboard as frequently and as much as possible is our advice. Up to 10cm / 4in is fine.
As well as retaining moisture, the mulch will slowly rot down and provide nutrients and trace elements not only for the current year but for a couple years afterwards when dug in after the crop has been harvested. It will also improve the texture of the soil. Mulch, mulch and more mulch is our rule.
Most gardeners grow their purple sprouting broccoli together in a single bed. However, if you are growing only five or six plants it may well be convenient to plant them around your garden /allotment as single plants in different locations. This is unlikely to be a problem as far a crop rotation is concerned because of the lack of planting density and the likelihood that the positions will vary each year.
The dates for planting out Purple Sprouting Broccoli will vary significantly depending on the weather conditions over the previous couple of months. However, an accurate guide is to plant into their final positions when they reach a height of 12cm / 5in. For early varieties this is likely to be around first week of July. For late varieties this is likely to be around second week of July
Make a hole in the soil, roughly the same size as the rootball of the broccoli to planted, place the plant in the hole and firm down well with your hands. Sprinkle a handful of fish, blood and bone fertileser around each plant and then water. Label the variety.
Leave a gap of at least 45cm (18in) between each plant, this may look a lot when they are young but they will grow to occupy a large area.
Purple sprouting broccoli does best when fed well with a nitrogen rich fertiliser, especially in the initial stages of growth. A feed with Growmore fertiliser once a month up to the end of October will provide a sufficient level of nitrogen. An additional feed of fish, blood and bone (a handful per plant) in September will keep up other nutrient levels.
In dry conditions keep the plants well watered. Examine the plants each month and remove any yellowing leaves, these will only encourage diseases.
Soon after you plant out your purple sprouting broccoli you need to make a decision on what level of pest prevention you want to take. Pigeons, cabbage white caterpillars and cabbage root fly are your enemies. The likelihood of suffering from these pests is impossible to predict – some locations will suffer, some will not.
All can be prevented by covering your crop with a mesh. Our article on insect mesh netting explores the options commonly available.
In warm summers purple sprouting broccoli will often bolt – the flowers open prematurely in an attempt to produce seed. In the UK weather it’s not actually the warm air temperature which causes bolting, it is the temperature of the soil which causes it.
To avoid this, apply mulch to the soil as soon in the season as possible. A layer of cardboard topped with organic matter such as grass clippings or wood chip will do an excellent job of reducing soil temperature and conserving moisture.
Purple sprouting broccoli is a tall plant and when fully grown may need supporting with a stake. Do this in October before strong winter winds batter them.
Harvesting purple sprouting broccoli is easy. The central spear will form first followed by several side shoots. See the picture below.
Purple sprouting broccoli shoots
Harvest the central spear first, do this before the mass of purple flowers open. This will then encourage more side shoots to open. These can be harvested over the next month or, making sure they are harvested before the purple flowers open.
Purple sprouting broccoli is best eaten as soon as it is harvested. It will store for a couple of days in the fridge.
RECOMMENDED VARIETIES OF PURPLE SPROUTING BROCCOLI
There are several of Purple Sprouting Broccoli seed for sale in the UK. The most common variety (and the cheapest is generic “Broccoli Purple Sprouting” offered by many seed companies. It reliably produces decent sized spears on health plants.
Of the F1 varieties, our vote goes to “Red Arrow”. Similar to “Broccoli Purple Sprouting”, it does however normally cost over two times as much.
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