Hi Eugene...What type of nutrition was your lemon lacking? Summer is when citrus put on most of their growth. With longer, sunnier days, humidity, fertilizing.
Was your lemon getting adequate sun? Toni

I think Toni's answer is likely exactly correct in Illinois, but in Central Florida, yes, we get a heat-induced summer dormancy. We normally get a good flush of growth in June, then nothing at all until at least September. Our trees have just begun the fall flush, I noticed the other day.

Malcolm,...I have a question..so, if temps in Fl exceed, say 105F degrees, growth on citrus halts? Then after temps drop, they continue growing?
If this is what you mean, it's amazing..
Growth here in Il continues until Sept, or so, then stops until after Feb/Mar..Although fruit continues to grow/mature during winter months..Toni

Yes citrus can stop growing for a time during extreme temperatures. When the transpiration rate exceeds their ability to uptake water they will sort of shut down and go into survival mode.

Toni, right, except that we never, ever reach 105. We only get to 100 about once in 5 years. But from mid-June through mid-September, we'll go above 90 every day, and July and August, at least 95 every day, with night temperatures falling only into the high 70s all that time. We've not had a night below 70 since May. 74 tonight. So we normally get a big growth flush in early June, then no growth at all until about now. Under our summer conditions (unlike in the North, where you get breaks from the heat now and then), plants which use the C3 photosynthetic method (citrus are prime examples) barely break even on their energy collection balance. Photorespiration, a process which uses the photosynthetic machinery, but which wastes energy, becomes a serious drain on energy resources when temps are high and in bright light. So trees (not just citrus, also the pecans, magnolias, etc.) in our type of climate make most of their net carbon gains in the spring and fall, and therefore, that's when the tree has enough energy to actually grow. The high night temps add to the problem, in that they keep the "normal" respiration rate high, burning off even more energy.

Plants which use the C4 pathway, such as sugarcane, corn, sorghum, redroot pigweed, Johnsongrass, just grow faster and faster, as it heats up. They love high temps, as long as they have adequate water. That's because they do hardly any photorespiration. But the C3 plants (99.6% of the earth's species, and almost all of our commonly grown crops) really are not well-adapted to growing during such weather; rather, they are adapted to surviving it while waiting for cooler temps.

Thank you, Malcolm.
When I said, 105F, I was giving an example.
So, what happens during winter months in FL? Say between Nov-Feb? Do citrus continue growing or do they go dormant?
Also, which months, IYO, would you say citrus do most of their growing? Fruit?
I've assuming most of Fl is humid, right? How does humidity fit in the picture?
Have you ever lived in a cold climate area? If so, did you grow citrus? If you did, how do you compare Fl vs X state? Thanks, Toni

Oranges, grapefruit, and mandarins do go into a winter dormancy here, especially if budded to a cold-hardy rootstock. Swingle, for example, appears to give most of the cold-hardiness to its scion by forcing the scion to go dormant. So we get a huge growth flush in the spring, with the bloom peaking usually the 2nd or 3rd week in March (earlier farther south). Then there is another growth flush, as already mentioned, in early June, often with a second, smaller bloom (which generally produces fruit of poor quality), and then the final flush is occurring now, in late September. Those varieties (limes, lemons other than Meyer, citrons, etc.) which are notoriously non-cold-hardy are so because they fail to go into a good dormancy, often bursting into growth in the winter, and then freezing. That is the primary reason those species are not hardy.

I was born in NW Pennsylvania, but moved to Florida when 11 years old. I had an interest in plants back then, but not citrus.