Sweet corn is one of the UK’s favourite vegetables, with its sweetness and versatility making it an instant hit on dining tables around the country. But, have you ever tried your hand at growing sweet corn yourself? If you have, you may have been intrigued simply watching this plant grow before it even begins to sprout these tasty cobs of corn! The stages of sweet corn growth are all intriguing to witness, from the germination that occurs so quickly after planting to the maturity of the plant when the cobs are ready to pick. And, if you’re ready to start growing sweet corn, understanding the sweet corn growing stages is vital to know that your plant is healthy and well. So, here’s a definitive list of the stages of sweet corn growth so you can understand where your plant is up to every step of the way.
One of the most important stages of sweet corn growth is the planting. If you plant sweet corn at the wrong time or in the wrong conditions, it will not grow to its full potential.
You should start planting sweetcorn in late winter or early spring, when outdoor temperatures permit. The soil needs to be at least 10°c to lessen the likelihood of pests and give the corn the right environment to grow. Usually, in the UK, the best time to sow sweet corn outdoors is in late spring, preferably in June when the weather is warm enough. However, if you are growing in a large polytunnel, you can sow your sweet corn in early to mid May and plant it out in late May.
When planting corn, you should grow them in blocks in your polytunnel greenhouse, rather than rows. Sweet corn is wind pollinated, so you should try to sow them around 45 cm apart in groups of two or three. As the roots of sweet corn are relatively shallow, they’ll only need to be sown a couple of inches into the soil. Then, you can thin out the extra seedlings to ensure the strongest one is left to grow.
With adequate watering and soil temperature, the seed will absorb the moisture and begin germination. In order for germination to start, it is best to water sweet corn seeds once a week with about an inch of water. Once seeds are planted and settled, metabolic reactions will begin almost immediately. So, germination can begin as soon as 2 or 3 days after planting, with the emergence of the radical from the seed beginning to show. However, this depends on the environmental conditions.
The time it takes for a visual change in the seeds can vary depending on the planting depth and surface area of the seeds and the temperature and moisture of the soil. If these conditions are not the best, the germination process can take as long as 2 weeks.
The vegetative stages of sweet corn growth occur between germination and flowering. This is where your sweet corn is carrying out photosynthesis and gathering resources for continued growth.
During vegetative growth, you can expect the beginning of the coleoptile, or the sheath that protects the plant, to start emerging. However, no leaf growth will be visible until the initial emergence is complete. This first visible leaf is easily identifiable since it is the only leaf that has a rounded end. After this, the leaves of your sweet corn will have a pointed tip.
When the growing point moves above the soil following its reliance on photosynthesis for nutrients rather than the seed, tillers will begin to become visible. Tillers are small branches that grow from the lower nodes of the plant and are morphologically identical to the main stalk. Additionally, ears and tassels (female and male structures, respectively) will also start to appear. As the plant moves into its sexual development stages of growth, these structures will undergo further development.
Towards the end of its vegetative growth stage, as the corn continues to mature, it will transition into a phase of rapid growth. During this time, you can expect any lower leaves that won’t bear ears of corn to die off.
Shaping and Development
As shaping and sexual development begins in another of the most important sweet corn growing stages, the plant will carry on growing quickly and start to take on the classic corn shape. During this time, many ear shoots, or potential ears of corn, will begin to appear along the length of the plant. The ear shoots you can see on the upper length of the plant are the shoots that will become full ears of corn.
As well as ear shoots, you should begin to see the development of tassel formations all over the corn too.
Since the plant will be greatly accumulating nutrients and dry weights, it will need plenty of extra moisture during this time. Plus, it would be beneficial for you to consistently maintain the plant for a better overall yield come harvest time. So, make sure to keep your eye on it and understand what the plant needs. For example, you may have to test the soil fertility and add mulch if it is not fertile enough. Or, you may have to check the moisture level and adjust your watering accordingly. Try to tune in to what the plant is telling you it needs.
Leaf Production End
The final stage of vegetative growth is easily identifiable by the corn tassels. By this point, they should be fully extended, although the silks will not have emerged yet. Usually, these tassels will be completely visible around 2 to 3 days before the emergence of the silks.
Although the leaves may grow larger during the upcoming reproductive growth stages, you will not see any new leaves appear after the end of the vegetative growth. Finally, during the end of the corn’s leaf production, the plant will shed its pollen. This is to prepare it for the beginning of the reproductive stages.
As the reproductive stages of sweet corn growth begin, the corn has fully grown but the ears are still maturing. By this point, the complete number of kernels and rows on the ears is determined, so the plant can focus on reproduction through the development of kernels in their husks.
Reproduction begins with the emergence of the silks from the ends of the husks. These silks work to gather pollen that falls from the matured tassels and move it down to the ovule, where pollination takes place. During this stage, the plant is at its most vulnerable, so you must monitor it carefully to ensure it encounters little stress.
Reproduction also sees the first kernels appearing on the corn. These will be small and white, with a clear inner fluid. A discoloured fluid genuinely indicates that the plant has a disease. As these kernels develop, the silks will begin to turn the recognisable brown colour.
The final stage of reproduction is the changing of the colour kernel from white to the classic yellow. By now, the kernels have started to accumulate starch, which will turn the clear inner liquid to a more creamy substance and start turning the kernels yellow. The cobs will grow drastically larger than the previous stage, although stress can cause the cobs to not reach their full size. As starch accumulation and a decrease of moisture continues, the appearance of dents in kernels will appear and the texture within the kernels will become stiffer to the touch.
The last of our sweet corn growing stages is maturity, where the corn achieves its maximum amount of dry matter accumulation and reaches its physiological maturity.
By this point, the black abscission layer where the kernels attach to the cob has formed, signifying that the kernels have fully developed. Plus, the starch that was on top of the kernels has now reached the cob, providing them with a deep yellow colour and a high moisture content.
How Long Does Corn Take To Grow?
It usually takes around six – eight weeks for cobs to complete the stages of sweet corn growth after planting out. The majority of sweetcorn is fully grown and ready to harvest throughout August and September in the UK, for reference.
When Is Sweetcorn Ready To Pick?
Corn cobs are ready to be picked when the silks coming out of the cob ends begin to turn dark brown. If you’re unsure when a sweet corn cob is ready to pick, you can try the fingernail test. Peel back the delicate top of the protective sheath and firmly push a fingernail into a kernel. If it leaks a creamy liquid, the corn is ready to harvest. However, if the liquid is watery, it is not yet ready. On the other hand, if the liquid is like a paste or no liquid comes out at all, then the cob is past its best.
How To Harvest Sweet Corn
Once you have determined that your plant has reached the end of all the stages of sweet corn growth and is ready to harvest, you can start picking! To harvest sweet corn, you can twist the ripe corn cobs and pull them sharply off the stem. However, after picking, sweet corn begins to rapidly lose its flavour. So, you should only harvest it when necessary and eat it as soon as possible.
How To Store Sweet Corn
Since sweet corn loses its flavour rather quickly after harvesting, you will have to store it well to keep it tasting sweet. First, remove the majority of the shucks, but leave a covering of at least 2 leaves deep. This should prevent the kernels from drying out as quickly. Then, place corn cobs in separate loose bags, not tightly sealed ones, since this can cause mould to grow. Finally, place the bagged corn in the fridge. It’s best to use freshly stored corn within two days.
Follow These Stages of Sweet Corn Growth In Your Vegetable Garden
The stages of sweet corn growth are interesting to witness, and knowing what’s going on during each of them is even more interesting! Now, you can follow along with your plant with a better understanding of what is happening, and better knowledge with which to treat each stage.
The UK’s top 20 favourite vegetables revealed! | Virgin Radio UK. 2023. The UK’s top 20 favourite vegetables revealed! | Virgin Radio UK. [ONLINE] Available at: https://virginradio.co.uk/entertainment/76614/the-uks-top-20-favourite-vegetables-revealed [Accessed 07 March 2023].
Sustainable Market Farming. 2023. soil temperature for sweet corn planting – Sustainable Market Farming. [ONLINE] Available at: https://www.sustainablemarketfarming.com/tag/soil-temperature-for-sweet-corn-planting/ . [Accessed 07 March 2023].
Sean Barker is the MD of First Tunnels, and is enthusiastic about providing quality gardening supplies to gardeners across the UK