Do stainless steel spades have any advantage?
Sometimes - they resist rust, which is handy for careless gardeners who neglect to clean their spade after use. A rusty spade tends to clog with soil, making digging much harder.
But note that a quality forged steel spade is stronger and more easily sharpened. Either sort will last longer with a little care: clean after use and rub over with an oily rag to help preserve the metal. Wooden handles benefit from an occasional rub with boiled linseed oil.
Is it true that sweet corn is best planted in clumps rather than in a straight line?
Yes. Corn is wind-pollinated, so clumps or short parallel rows are preferable. Planting sweet corn around other vegetables can make a useful windshield, but be prepared to stake tall, exposed plants. Wait until the weather warms up before sowing, though, corn is frost tender. You could start plants in the greenhouse or under cloches, but direct sowing is best.
If you have a gardening question, email Glenys at firstname.lastname@example.org