I'd just fold down the 2nd row seat(s) and spread the load over a wider area.

 

So true. I did it every two weeks. Just don't do it everyday; it will wear down the suspension prematurely.

 

Page 650 in the manual. Here's a screen shot of it. Look like 1500 pounds is max including occupants.

 

That 1500 lb looks like for the 4cyl Highlander, and the Platinum looks like 1280 lb.

 

You have a brand new vehicle so why take a chance . That much weight will effect handling and stopping distance. Just make several trips .

 

I'm just speculating, but....

Perhaps @Platinum2018 was intending on using the 2nd row space as well, by folding the seats or row down.
40 bags...Each bag is about 4" tall and about 16" wide and 37" long(I'm guessing for at least a 35lb of fertilizer.
You can get maybe 3 rows, but only stack about 8 bags high. Before you know it, that space is full.

So for 40 bags it is only logical he would be using more of the 40x47x35" space. Otherwise he would likely get about 25 bags in.

I have the AirBags for the suspension, and yet to install. I load my back with a good amount of gear, but nothing that dense.

 

I think Home Depot or Menards will rent you a truck for $20.00 for 75 minutes.

 

Based on the weight limits stated in the manual, it's probably not advised. Speaking from personal experience, I've done it. First week of owning my 2017 HL XLE, I picked up 30 bags of pond stone from Lowe's (42lbs per bag) = 1260lbs. Also had myself and another passenger in the car for a total of about 1700lbs (limit 1280). This is my first SUV of any kind and I hadn't given any thought to a weight limit or the possibility of even coming close. Nothing eventful happened at all, I didn't notice anything change in any signifiant way to handling or braking distance. There also was not any noticeable sag or lowering of the car on the suspension with the load in the back. Given the chance for a do over, it probably wasn't a wise thing to do, but given the outcome and performance, I'd bet that those weight limits in the manual are quite a bit understated from the actual limits, to remove Toyota of any responsibility in the event of a crash / suspension failure /etc.

tl;dr
Not recommended but probably fine

 

I'm comfortable loading 50 lbs. bags, one at a time. 40 lbs is a bit too easy, and I have to make more trips. 80 lbs. bags are a bit of a struggle, and 100 lbs bags are just too much strain. So, I'd say 50 lbs. bags are comfortable. :wink: