|Loose-leaf lettuce planted from the nursery turns bitter in a couple of weeks. From seed, it is bitter by the time it is an inch high. Onion sets that used to grow quite large now get only an inch or two in diameter and then go to seed. Freesias that are supposed to bloom blue are invariably pink. My soil is well enriched with compost but it is alkaline, typical San Gabriel clay. Cause? Thanks|
|Bitterness in lettuce and onion sets that go to seed are typically due to weather conditions, not soil. Lettuce grows best in the cool weather so planting in November or December should give you several weeks of harvesting before the leaves begin to taste bitter and the plants go to seed. Onion sets should be planted in the fall and if you see a seed head forming, cut it off at ground level so the plant's energy is redirected into the roots rather than seed production. You can try planting in containers filled with potting soil rather than in the ground to see if you have better results but I suspect that timing rather than soil conditions are the cause of the problems.
Hybrid freesias do not change color with soil pH as some hydrangeas might do, but freesias can self sow and those offspring can revert to standard colors such as white or cream, or even pink. If you're concerned about your soil's pH, you can amend the soil with compost and apply elemental sulfur to help lower the pH. A soil test will give you an exact number and you can then make one or more applications of sulfur (depending upon the soil test results) to help lower the pH. Best wishes with your garden!