Laravel sort collection by date

I have this collection result:

$result = [{
    "date": "2016-03-21",
    "total_earned": "101214.00"
},
{
    "date": "2016-03-22",
    "total_earned": "94334.00"
},
{
    "date": "2016-03-23",
    "total_earned": "96422.00"
},
{
    "date": "2016-02-23",
    "total_earned": 0
},
{
    "date": "2016-02-24",
    "total_earned": 0
},
{
    "date": "2016-02-25",
    "total_earned": 0
}]

I want to sort the result by date:

$sorted = $transaction->sortBy('date')->values()->all();

But I don't get the expected result:

[{
    "date": "2016-02-23",
    "total_earned": 0

},
{
    "date": "2016-02-24",
    "total_earned": 0
},
{
    "date": "2016-02-25",
    "total_earned": 0
},
{
    "date": "2016-03-22",
    "total_earned": "94334.00"
},
{
    "date": "2016-03-21",
    "total_earned": "101214.00"
},
{
    "date": "2016-03-23",
    "total_earned": "96422.00"
}]

As you can see all with month 2 is sort properly. However at month 3 it start messed up. (the real result is longer than this and it messed up start at month 3)

Any solution to make it sort properly?

Thanks.