Mowing when the grass is wet or too tall, or both will cause clumps, but I have always used a mulching mower, mowed when the grass is dry, and never let it get too tall. Occasional clumps are not a cause for angst at my house.

With St Augustine grass in the south, you have to keep mowing over it if you have any long pieces sitting on top of the grass. If you don't then it cuts off the air to help evaporation of morning dew, and the lawn will often get a fungal disease. My grass is probably 9 inches high right now due to rains for the past 15 days. I will be pre-mowing with a string trimmer to get it low enough for the mower to work right.

as saypoint pointed out, tall wet grass is difficult to cut neatly. the quality and effectiveness of the cut has a lot to do with the mower also.

Dchall, wow, string trimmer! I hope your lawn isn’t too big.

This is why you need discharge capability. It's pointless to even try to mulch when the grass is wet/tall. My rule is, if the tires get wet its too wet to mulch. This is also a big reason mowers can go up to 4 1/2" - you set up for discharge and cut it as high as you can. If it doesn't rain, you can go back the next day, drop it 1" and either bag or discharge depending on the circumstances. All over my area you find clumps of 'pureed' grass all over the yards and edges of the streets because morons will not raise their cut and discharge instead of mulching.

I agree that clumping of grass is an indication of either cutting grass that is to wet or too long . The second affect can be caused more often when combined with too quick of rate of cut (speed of mower). When mowing with a push mower a sharp and proper blade design is paramount . Tractor or zero turn mowers again require proper blade sharpness & design and rate of cut for the grass conditions , but also proper mower deck alignment . In dchall,s example bagging would be the optimum mode for thick / dense grass which has entrained moisture . Mulching only contributes or promotes potential for fungal disease . Mulching can help stimulate lush grass in a healthy lawn however will quickly spread or contaminate lawns that have weed growth or disease . Direct discharging can be utilized on smaller lawns when extended heavy rain has caused lawn to grow longer than is practical for the cutting mode normally utilized . Unfortunately each mower manufacturer has limitations of which mode it's unit can provide quality cuts due to mower deck design or cutting blade parameters .

I once had a Honda with the Xenoy deck and 160 GCV. It had a rear discharge port but a discharge chute was available with a bend to throw the clippings to the side, away from the operator. It also had a steel plate inside to prevent hard items from breaking through and hitting the operator. Anyway the point is I used that chute a few times when the grass was too wet/tall for mulching and it did a great job distributing the cuttings without making windrows. Being higher up than most discharge ports probably was the main factor. I have also noticed my new 30" single-blade riding mower does a tremendous job on mulching or discharging. Probably due to the long single blade more than anything else. I run it with the deck at one notch below top height which seems to be about equal to 3" on a walk-behind.

Actually with my New Commercial Toro 2 1" Self Propelled i can mulch 4" even when wet , probably the Gator blade combined with 6 HP Kawi Engine . I have side discharged 8" dry clover by the Horse Padock and routinely bag 4 -6 " in the Spring and Fall . Some mowers mulch and others only bag well . The mower deck is the main reason in most instances that I have witnessed . As Tom plum has advised on many threads trial and error indicates only so much can be done to correct bad engineering . Common sense dictates don,t bite off more than you can chew !

Nathan, You can compile your data and test your theory at Smiley Park.