I did not pinch out the top shoots on my sweet peas after the first 2 leaves formed. They are not growing well and are now only about 6 inches high with about 6 leaves on each stem. Is it too late to pinch out tops now and will this help their growth?
No it is not too late ...I wouldn't pinch out at 2 leaves anyway but would wait for the plant to be a bit bigger/stronger. SPs like water and feed. Tomorite at half strength each time you water should get them going. Water every day or every other day, or the bottom half will go brown. Pick flowers very regularly. If you let them seed they think they have done their thing for the year and give up. Last year Monty Don said pick ALL the flowers once a week, even those in bud. I think this was good advice.
They like warmth too so if you have a nice sunny spot....if they are in a pot of course.