A quick overview for the beginner on growing sweetcorn for food in planters, based on my own experiences.
Varieties Grown: Golden Bantam
Site: Full Sun – the more the better
Grown In: Multi Purpose Compost
Container Size: 8″ (20cm) minimum depth to start with, plus ability to add another 6″ (15cm) of depth (by “earthing up”) when bottom of stems start producing roots. Sweetcorn is wind pollinated as there are male flowers on top which drops the pollen onto the female flowers below when the wind blows. Because of this you want your corn in a block rather than in a line for best pollination. You could grow them in trough planters if they are deep enough, but put a few planters together and try to get groups of plants at least 3 wide x 3 deep. I grew mine in a large round vegetable grow bag with reasonable success (though I didn’t quite achieve the depths required). Spacing is recommended as 12″, although this can be reduced to 8″ if you have a good regime of watering and feeding so they aren’t squabbling with their neighbours for food and water. If you can’t spare the time to keep on top of feeding and watering, leave the spacing at 12″ – these are BIG plants
Root Structure: Have been likened to television aerials and for good reason. In deep soft soil they produce a main vertical root with horizontal side shoots, like an old television aerial pointing downwards. These are tall plants with large hungry/thirsty roots. The more soil/compost you can give them the better.
Feeding / Watering: I gave mine a good drink of a balanced plant food once a month, and they reached 8ft tall despite the limited depth of compost. I should have switched to a tomato plant food to help the ears of corn develop to their full potential, and I should have earthed up the plants so the stem roots could take hold to gain more nutrients – but my planter wasn’t deep enough. In order to ensure that I got some ears of corn to develop fully, I harvested all the smaller cobs from each plant as baby corn, just leaving one ear to develop fully. With a bit more soil depth, earthing up when stem rooting started, and switching to a fortnightly/monthly tomato food (dependent on number of plants fighting for the nutrients) when the ears started forming, I would have been able to let them all develop into full corn cobs bursting with goodness and flavour.
Harvesting: Pretty much when they go brown on their wrappers, the cobs should be ready for harvesting. If you squeeze them gently, you should be able to feel if the ears have swelled over their full lengths. If you pick them too early, they will be swollen at one end, but taper to not a lot at the other. The other option is to harvest earlier when the tassels are just turning brown for the most delicious baby corn you have ever tasted.
Companion Plants: Sunflower. The nasties go there rather than the corn. Put this in a separate (and DEEP) planter next to the corn. They are also very hungry and thirsty, and put down quite a long tap root, so they will be stunted if your planter isn’t deep enough. Ideally the planter wants to be at least 30″ deep (75cm) x 16″ (40cm) across. Feed and water generously like with the corn, and switch to tomato food when the bud starts forming. Sunflower can also be grown as a crop in it’s own right. Some varieties give edible seeds (you need to have somewhere to dry the flower head out where it won’t go mouldy), or the flower bud can be harvested and cooked like globe artichoke, or the seeds can just be sprouted to a few inches long and eaten like that either raw or in a stir fry. Sunflower sprouts (or Sunnies) are apparently quite popular in Australia
Standard common sense disclaimer:
This guide is purely based on my experience, in my garden, with my plants, grown at my hand. You may find that your plants respond differently and have different needs based on variety, strain, or other growing conditions. If you plants do not succeed as well as you hoped, fizzle out completely, or they uproot themselves and start terrorising the neighbourhood or hanging round street corners with malicious intent – you grew them, not me!
All In Containers 