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Corn-Cream of the crop! Grow me in December

February 3, 2025

Corn – Cream of the crop!

Mouth watering corn on the cob – it’s what every gardener aspires to grow. Unfortunately,  if it’s to produce a harvest, corn requires consistently warm soil (at least 20°C ), 6-8 hours of sunlight per day, and free draining soil. This isn’t something we can all guarantee our climate will provide. Which is where a tunnel house comes into its own. Tunnel houses help the soil warm up faster than that in an outdoor situation, they trap in heat, and they protect corn plants from the sort of heavy rain that can make soil gluggie and can spell disaster for our plants, especially at pollination time.

Giving over a portion of the tunnel house to corn can seem like a big commitment, but because cobs are mature within 90-110 days when grown from seedlings, the plants don’t occupy the ground for too long. And by waiting until December to plant out corn seedlings, we can use the space for growing spring vegetables before hand. What’s more, the richer you make your soil, the closer together you can plant the seedlings.

Ground work

Corn is a gross feed i.e. it enjoys rich, well-fertilised soil. While it’s certainly possible to grow the plants in less-than-ideal conditions, the result will be small cobs that won’t reach a desirable length or fill out as they should. So don’t stint on ground prep. To prepare your tunnel house bed to receive corn seedlings, choose a position where the plants (which can reach over a meter high) won’t shade other vegetables. To visualise the space your corn will require, bear in mind that the plants will be grown in a block (to assist with pollination) and that the seedlings will be spaced no closer than 30cm apart.

To create the excellent drainage that corn requires, loosen the ground deeply by pushing a garden fork into the soil to the full depth of its tines. Avoid actually digging up the ground as you will only be turning under good top soil. Instead, push the fork deep into the ground, and rock it back and forth to loosen the subsoil. Next, use the back of the fork’s tines to break up any clumps of soil to a depth of half the fork’s tines.

Corn prefers a less acid soil than tunnel house plants such as tomatoes, so if you are preparing the ground several months ahead of planting, scatter a handful of lime per square meter over the bed. Add to this a 3cm layer of sterilised compost, and 5-6 cups of sterilised manure pellets per square meter of ground. If you plan to use a general vegetable garden chemical fertiliser, use it at the rate suggested on the container. Fork all the ingredients into the soil along with some mycorrhizal fungi to promote nutrient acquisition, and water the ground at least twice over a period of two days prior to planting. While the bed absorbs the moisture, prepare a liquid manure feed of chopped kelp, sterilised compost, and comfrey leaves. Soak a bucket each of these ingredients in a covered barrel of fresh rain water.

 

Sourcing

It’s not difficult to grow your corn seedlings from seed but if you plan to do this, start them early enough so that they are at least 10-15cm high by the time you wish to transplant them. And always grow each seed in its own individual container, preferably one that can be planted into the ground along with the seedling. This is because corn plants resent root disturbance.

Because gardeners sown corn regularly throughout summer, seedlings will almost certainly be available at your garden centre in December. Choose varieties that mature in the shortest time so that you free up your tunnel house bed for another crop as soon as possible.

 

Transplanting

Corn seedlings may look robust but, in fact, they are slow to absorb moisture, and their delicate roots are easily damaged. Minimise disturbance by digging planting holes which are deep enough to receive the seedlings without their roots having to be ‘squashed down.’ Water each planting hole well, before popping in the seedlings, and again after the plants are in place. If the seedlings are in non-compostable containers, take great care with easing them out, and ensure as much soil as possible remains around the roots. Gently firm the soil around the base of each plant, and mulch with a light material (such as un-treated pea straw).

 

Maintenance

Corn is a shallow-rooted plant so it’s important not to disturb its roots once the seedlings are in the ground. Carefully hand weed to reduce any competition, and water weekly with the liquid feed you have prepared (corn will tolerate drier conditions than many other vegetable plants but regular watering will help with the formation of cobs). Keep roots damp but not moist with a layer of organic, untreated mulch.

 

Pollinating

In an outdoor gardening situation, wind does the work of shifting pollen from the male flower head  (the tassel at the top of the corn plant) onto the females ears or ‘silk’ that grow from what will eventually be the cobs. However, in the largely windless environment of the tunnel house, you, the grower, will have to do the work of pollinating. Each of the sticky threads on the silk is responsible for pollinating a single kernel of corn on the cob, so as you pollinate, it’s important to make sure that pollen reaches every thread. If it doesn’t, your corn cob will experience ‘blanks’ or missing kernels.

The yellow pollen on the tassels remains in place for about a week, with the most pollen being available toward the start of this period. As soon as you notice pollen on the tassels, go into the tunnel house and gently shake each corn plant so that pollen falls down onto the silks below. Do this each day until the tassels stop producing pollen.

Harvesting

It can be difficult to gauge just when the cobs are ready to harvest. A discolouration of the silk can help indicate ripeness but don’t give the whole picture. For a more accurate guide, gently pull back a little of the green sheath covering the cob and push a finger nail against a kernel. If a little milky liquid forms, that’s an indication the cob is ready to harvest.

Tips

Growing a minimum of 15 corn plants in a block assists with good pollination.

 

Plant the same variety of corn in each block to help with pollination.

 

Although it is traditional to grow runner beans with corn (because the corn provides a natural climbing frame for the beans) don’t attempt this in your tunnel house where conditions mean that the beans may overrun your corn plants.

 

If you wish to dry your corn, leave the ears on the plant to dry out, or pick earlier, scrape the kernels off with a knife, and place them in a dehydrator. When thoroughly dry, store the kernels in an airtight jar.