Zea mays convar. saccharata var. rugosa
Sweetcorn is a type of maize and both are in the Poaceae grass family. They are vigorous plants and easy to grow, but it’s less easy to achieve a harvest before others do – see ‘Pests’ below.
An example is badgers, who often strip sweetcorn plants at Homeacres just before I want to pick the cobs. They are powerful animals and difficult to keep out of a garden.
My remedy has been mainly not to grow sweetcorn, and this is one reason why there are fewer photos here than I would have liked.
Plants of sweetcorn grow tassels of flowers at the top, which drop pollen on the hairs of each cob. Every hair is attached to a potential kernel or grain of corn. If pollen drops or floats by, and is received by the green hairs, then kernels can swell to a full and juicy size. If not, cobs are empty or have gaps. The cobs have an outer sheath of green leaves, wrapped tightly around.
- In American English, cobs are ears and hairs are silks. The outer sheath of leaves is a husk.
In the 1990s I lived in Southwest France, where maize is grown a lot for harvest as dry grain, some of which goes to feed poultry. Seeing how easy the climate is for growing sweetcorn, I grew and harvested some to sell on my market stall in the local village.
- I thought that they would love it, as a vegetable they had not thought of eating.
- The result was delicious sweetcorn and zero sales, with the common comment ‘this is duck food’!
Never mind, we know it is delicious! There are many varieties that have been bred to grow sweetcorn, rather than dry maize. They are an absolute treat when you harvest at the best time, before the pests do!
- Days from seed to first harvest: 80 for early varieties grown in warmth, commonly 95
Sweetcorn seeds sownCobs ready to harvestMid-spring under coverMidsummer to early autumnLate spring outsideLate summer to mid-autumn
- Best climate has warm summers, with afternoons of 21 °C/70 °F and higher, not too dry.
Why grow them
Homegrown sweetcorn, freshly picked, has significant dimensions of flavour and sweetness compared to cobs you can buy. One reason for this is that sugars in newly harvested cobs start to convert to starch after being picked. Therefore, when you buy sweetcorn it’s usually less sweet than homegrown. It probably has fewer other flavours too, because the field soil is unlikely to be as healthy and fertile as your soil.
The hybrid supersweet varieties do retain sweetness for longer after picking, compared to older varieties. As do the varieties I recommend here, bred in Germany where they have concentrated on maintaining sweetness after harvest.
Pattern of growth
Plants grow rapidly in warmth, up to 1.5–1.8 m/5–6 ft high, according to the variety grown.
Sweetcorn cobs contain hundreds of immature seeds, the kernels we value, which grow to dry seed if not picked when fresh and sweet. They are an annual plant, which in nature will regrow the following year from any seeds that survive the winter. In our case, we need to either save our own seeds (difficult, see below) or buy new seeds every spring.
Plants are killed by frost, so the growing season is limited either end by the last and first frost dates. Sweetcorn’s growth and harvest timings are governed by season length and the warmth of days in summer.
- If your summers are normally cool, it’s worth raising transplants under cover to have them ready straight after the last frost date.
- In cool regions you can grow sweetcorn in a polytunnel.
Suitable for containers/shade?
These warmth-loving plants grow better in full sun. They are also large, with extensive root runs, and so I do not recommend them for containers.
However, if this is your only option, it is possible to grow two plants per 15 litre/4 gallon container. They will need feeding plus a lot of watering, and also some staking and securing to stop the container from blowing over once the corn plants are quite tall.
Two German-bred varieties called Mezdi and Tramunt give amazing results here. The former matures about two weeks earlier, while the latter uses those extra two weeks to grow fatter and sweeter. They are open-pollinated, yet retain sweetness for up to two days after harvest. Neither of them matures super early.
I find that the earliest varieties do not grow the largest or sweetest cobs. However in colder climates they are worth growing, in order to ensure growing time for kernels to sweeten. Best consult your local seed sellers.
Earlibird is more mid-season than early and grows an excellent harvest.
Northern Extra Sweet is a little later and with no extra sweetness that I noticed, but the harvest is bountiful.
In F1 hybrids I recommend Sweet Nugget, for good size cobs which retain sweetness.
Minipop F1 is a babycorn variety that can grow up to five small cobs per plant.
You can grow popcorn in the garden, but I have no experience of this because it needs a summer hot enough to mature cobs with dry grains. Rodents can be a problem because they like unpopped corn.
Sow and propagate
Mice adore sweetcorn seeds, so you may need to keep a trap set, close to new sowings under cover. Outside this is less practical and you have to hope perhaps that a cat is patrolling, if mice are a problem in your garden.
Sweetcorn plants are not only killed by frost, but they also do not grow strongly in cool conditions, such as during much of early May in our climate.
- If you sow or plant too early, or just before cold weather, seedlings grow slowly and the leaves will be yellow from a lack of nitrogen. There is no shortage of nitrogen in the soil, it’s just too cool for sweetcorn roots to function so they can access it.
- Seeds germinate in four to seven days, depending on warmth.
Sow under cover in mid to late spring, three to four weeks before your date of last frost. Here we sow in modules on 15th–20th April, and outside from about mid-May.
Sow at 1 cm/0.5 in depth in medium-sized modules, 4–5 cm/up to 2 in wide and deep, both horizontal and vertical. Seedlings grow a strong taproot, whose inability to grow downwards in modules does not compromise subsequent growth. There is no need to use expensive ‘root trainers’, which are extra deep modules.
Allow up to one month from sowing to transplanting; we transplant around 20th May.
I do not recommend this extra work, which also requires extra space under cover. It’s more efficient to delay your sowing until three to four weeks before you are ready to transplant.
‘Two Sisters’ option, with plants in a line
It’s sometimes recommended to grow sweetcorn among beans and squash, as ideal companion plants. This comes from native Americans, but their harvests were dry corn and dry beans, not sweetcorn and bean pods. They also had hot summers.
I find that Two Sisters can work in a more temperate climate. Plant winter squash at 1 m/3 ft apart, and pop in two or three sweetcorn transplants between each squash plant. The pattern of growth is complementary and it feels like a free crop of sweetcorn, from a space where the squash were growing anyway.
- Usually it’s reckoned that you need to grow corn in blocks, so that cobs grow with a full set of kernels thanks to even pollination. More pollen ‘should drop on their tassels, coming from all directions of the block and whatever the wind’.
- And yet, I find that sweetcorn grown as a ‘sister’, in a line rather than a block, still pollinates successfully. Have a go and see! No dig makes it easy because keeping the ground weed-free between all these plants is so manageable.
Transplant size and time
Transplants do not need to be large. I sometimes read that they should be 15 cm/6 in high and, while that can work, it’s absolutely not a rule. We normally transplant when seedlings are approximately 10 cm/4 in high, as in the photo above.
If there is a small risk of even a slight frost after transplanting, I would cover plants with fleece. Lay it over hoops for better frost protection, because the fleece is then not touching the leaves when it might freeze at dawn.
It’s quick to pop in module-raised plants, using a dibber to make holes for them. Make holes deep enough that the top of each module’s compost is about 2.5 cm/1 in below surface level.
- You don’t need to fill the holes, just water after transplanting and again every two days if the weather is dry, until you see strong new growth.
Space equidistantly at around 30 cm/12 in – this usually gives four rows along a 1.2 m/4 ft bed. You could plant at 25 cm/10 in for early varieties, and at two plants per metre/39 in along the row, when intercropping between squash.
Use this same spacing for growing baby corn, which grows on plants of the same size. The difference is that your harvest is several mini cobs, rather than one or two bigger ones.
This should not be necessary.
If your site is so windy that sweetcorn plants need support, it’s probably not a good place to be growing this warmth-loving and quite tall plant.
In a dry summer, water once you see a first browning of cob tassels, because this is when cobs are starting to swell. In hot weather, when soil is really dry, you will notice the leaves start to curl inwards to conserve moisture.
In arid climates and conditions you need to give a lot of water because sweetcorn grows fast and needs it. I was in Zambia in spring 1992 when the maize crop was failing from lack of rain. Meanwhile, the millet and sorghum were still giving harvests, but less than the maize would give if it had rained.
Extra mulch to retain moisture?
This is definitely a good plan if your summers are normally dry, and you still need to water in very dry weather.
Plants grow sideshoots of small new stems from the base. Opinions vary as to whether it’s worth removing these and I have tried both removing them and leaving them, with little subsequent difference to the harvest. The shoots may grow a very small cob, which is hardly worthwhile.
On the main stem, there is often a second and smaller cob below the main one. I find that it rarely fills with many plump kernels, except in a hot summer. It may be worth removing in early summer, if your climate is cool.
How to judge readiness
Indications of sweetcorn being ready include the tassels being mostly dark brown and also perhaps the corn being eaten by pests! You can check more precisely by using a thumbnail to ease apart the outer sheath of a fat cob, wide enough to see the kernels beneath.
- They need to look plump, but not necessarily dark yellow because the colour deepens during cooking. It’s exciting to pick the first cobs and see what they taste like.
- Baby corn comes ready about a month earlier than sweetcorn and cobs need harvesting seriously small – snap one off to check. Here that would be in early July. After stripping the sheath leaves, each cob is around 10–15 cm/4–6 in long, with the tassels usually still green in colour.
How to pick
Place your fingers around the cob you want to harvest, and push gently downwards until its stalk snaps from the main stem. Just above the cob, use your other hand to hold the main stem upright, which ensures a cleaner snap of the cob stalk and no damage to the plant stem.
When to pick and how often
Harvests from one planting may continue for a month, during which time the kernels become darker, firmer and sweeter. Eventually, the texture toughens and sweetness is hardly there any more.
- Later picking of mature cobs gives more quantity, but with less sweetness.
I would not attempt this for more than two or three days. Homegrown sweetcorn is a treat to enjoy when it’s picked super fresh. It is something you cannot buy!
Pollen from the male flowers or tassels can be blown for more than a mile/1.6 km in the wind. If you want to save seed, and with the variety true to type, you need a long distance between sweetcorn of any different varieties. I would say this is not something for most gardeners to attempt, and I have not done so.
Birds, mice, and squirrels adore sweetcorn as much as we do. Keeping them off is not easy, and often the best remedy is to pick your cobs slightly immature, before too much damage occurs.
Badgers (Meles meles)
These powerful animals have a sweet tooth and a determined manner. If in your area, you may suffer major loss of strawberries, sweetcorn, carrots, peas and also fruit such as apples.
Badgers are not deterred by mesh or electric fencing, being simply too strong. With an electric fence, they don’t see it and may well charge through, take the shock and then eat while recovering!
They damage plant leaves and stems while searching for and eating their harvest. This is why I did not grow corn for several years – I did not want them in the garden. I got lucky and we enjoyed harvests until one or two badgers discovered the sweetcorn – within two days it was all smashed to the ground and eaten. A problem with badgers is that they cause so much other damage.
None to report!
The tough and fibrous roots stand above soil level. This allows you to cut them with either a very sharp knife or a sharp spade, at surface level. Leave most roots in the ground, clear any weeds and you are ready to replant.
Early harvests allow time for many subsequent plantings, such as autumn salads, salad onions and spring cabbage. Spread compost before any plantings that will grow through winter.