Lettuce seeds will not always germinate when soil temperatures are too high normally the height of Summer approx. above 26 degrees Celsius. This is normal and does not indicate poor germinating seed, sow them again in the Autumn or Spring.
There is also the probability that all lettuces, when grown in hot conditions will bolt to seed quickly, especially when a cool period precedes this.
Icebergs are hard to grow and very specialist plants for specific growing regions. In certain conditions they will not head properly no matter how good the variety or regional variation may be, these conditions include very warm weather, intense sunny weather following very cool periods.
This is because the plant gets set back when trying to form the head, classic signs are pale leaves, poor head, burnt tips of the leaves, very bitter leaves, brown spots on the leaves.
A hardy variety that can be sown all year round requiring constant moisture and fertile soil. Great flavour. Sow: dig over raised beds, spread complete organic fertilizer; 4 litres to 10m². Top the bed with well rotted manure or mushroom compost and rake in. Sow seeds 5 mm deep and 30cm apart in short furrows in rows 40cm apart. Several sowings can be made throughout the year.
An open pollinated selection bred by Carole Deppe. An interesting variety that begins as a small pointed crown shaped plant and develops into a handsome 35cmx 35cm neat and well shaped green and gold open framed type with a wonderfully sweet flavour. Sow early Spring, and late Summer to early Autumn. Sow 5mm deep in rows 30cm apart. Thin at four leaf stage.
Selected varieties by Steve Solomon, which will provide you with a rich abundance of a variety of different lettuces, all are suitable for cool climates and are slow to bolt, sweet to taste and have soft leaves. Most are compact and have good hearts, but can be used as loose leaf lettuce as well. Prepare soil by raking in COF. Sow early Spring to mid-Summer and again in late Summer and Autumn. Sprinkle seeds in a small trench 5 mm deep. Cover with soil and water them in, seeds germinate in 7 to 12 days. When plants have four leaves thin them out to about 20cm apart and feed with COF.
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Happy gardening - wherever it may be!