>>I always thought nitrogen primarily promoted leaf/blade growth, so I'm not quite understanding the reasoning behind winterizing with nitrogen when the lawn has stopped growing. I'm not doubting this is a good idea, because you seem to really know what you're talking about, but I tend not to do things "just because" so would appreciate some insights.

Classically, N-P-K fertilization has been looked at as "Up, Down, and All Around." Or, nitrogen for Up (top growth), phosphorus for Down (root growth) and potassium for All Around (both top and root growth).

That's completely wrong, although excess nitrogen will certainly set off excess top growth if conditions are right for it (moderate temperatures, good rainfall, all other resources available in decent amounts).

Really, N-P-K fertilization is "All Around, All Around, All Around." All parts of the plant use all resources, just in differing amounts.

For winter, that last dose of nitrogen is absorbed by the roots, but temperatures are too cool for much top growth. Instead, it gets used in the food production factor to, indirectly, turn into sugar. Those carbohydrates are stored in the roots (which always happens when production exceeds demands) and used to keep the root alive over the winter.

Winterization--and carbohydrates in the root systems--can also help the grass stay greener during winter. The running joke around here is that my lawn looks the same in February, May, July, and October.

It's not true, May and October color and performance far outstrip February. So does July, just not by nearly as much. In my case, proper feeding and keeping my potassium levels fairly high (along with balancing all other resources right into the perfect grooves) mean the lawn is always happy, always fed correctly, and always willing to give it its best go at the situation. Very cold winters or sudden cold snaps of below 15° send even my lawn to sleep.

>>Also, why no organics between May 1 and Aug 1?

There's no need. A good organic feeding will provide a strong nitrogen release right when the lawn wants feeding (end of May through June) and a modest feeding through July.

Your lawn isn't particularly interested in eating heavily during summer, which is similar to winter. Growth is low, and it's mostly in a state of rest. If it can stay green, great, but if not some grasses are actually quite happy to go dormant and skip summer, returning in fall.

The August 1st feeding starts to release nitrogen just about the time high temperatures are dropping noticeably and growth is resuming.

It's not strictly an error to organically feed in summer, it's just not necessary and it doesn't do much for the lawn. For those who are aggressively trying to improve their organic matter levels or condition a soil, I don't object, per se, but would still move most of the heavy applications to May and August-October when the grass benefits more from it (and produces more greenery which you then mow off and rot back into the soil, further improving the OM, which feeds the lawn and produces more greenery...)

>>I get chopped leaves from neighbors to winter protect my hydrangeas. In the spring, can I periodically spread a reasonable amount over the lawn before it's cut to get those mulched into the lawn?

Yep! Amounts of up to a quarter inch (post chopping when they're smaller and more compact) are great at any time. A full trash bag of unchopped leaves can be applied to as little as 100 square feet or so if you chop very finely.

Nature's schedule is nice, but she also delivers plenty of blown leaves onto plants during spring and early summer. Not to mention sloughed off leaves from plants all through the spring and summer seasons.

Leaves will decay faster in the (generally) greater spring rainfall and rising temperatures, and the grass (and worms) don't care whether it's October or May.

FYI, the answer to your any of your questions will almost always be "It's more complicated than that" followed by the complete explanation!

It's been said here (Morph?) that organic fertilizer takes approx 3 weeks to break down and become available to the grass, but the synthetics are made available almost right away. With that in mind, you shouldn't put a synthetic application of fertilizer on August 1st because the grass doesn't need all of that N in the heat of summer. However, an August 1st organic application isn't used by the grass until the third week of August (around the time where temps drop significantly and the grass starts growing more) On the flip side, in cold weather the organics don't break down as quickly, which means the grass can go dormant before it gets enough N... That's why you want a synthetic for the last winterizing. Hope that makes more sense with the timing.

Actually, the answer is: "just because." Observation and experience does indicate that it is beneficial whatever the biology behind it.

There have been few studies and of those that have been made (at least as of five(?) or more years ago) don't correlate well with one another on methodology or results. Of those that measured cool season turf grass carbohydrate storage, it was universally found that plant carb reserves were higher for winterized turf vs an un-winterized control when measurement was taken the following spring. A logical conclusion would be that the turf is using the winterizer N to create and store carbs; however, the only test that actually measured turf carb reserves on a monthly basis during the winter months found that reserves were actually less during the winter months when compared to the control. It wasn't until the spring measurement that carb reserves increased.

Turf specialists, that have commented on this, postulate that the increased carb reserves found in the spring measurements may be due to the earlier spring "green-up" that occurs with winterized turf.

Based on this scant research, it appears unclear as to why winterized turf greens-up earlier, but experience does support observations that winterized turf and early spring green-up results in healthier, better appearance lawns. Likely this is due to reduced susceptibility to disease (less new, tender top growth with winterized vs un-winterized/spring fed turf) and/or maybe an increase in quality or quantity of root mass if the turf is using the increase in spring carb reserves for root growth during an expanded spring root production window due to earlier spring green-up.

And to extend to the psychology of it, when grass greens up early in the spring, owners should be less likely to want to dump fertilizer on it to keep up with their neighbor's winterized lawns. No research for that either other than reading these forums for too many years. We hardly ever get posts from people complaining about their grass greening too early and "What should I do about it?" But when it is the last lawn on the block to green up, we do hear from people who have already applied too much of something and are wondering whether it's safe to add more stuff.

A lot more helpful information was added - thanks to each of you. It makes a lot more logical sense now (including the "just because" explanation yardtractor added) and it's help move me past the "I read it on the Internet" explanation, which is about all I would have been able to come up with if someone asked me WHY I was doing what I'm doing.