From The Free Dictionary Dot Com:

go to seed
1. and run to seed Lit. [for a plant] to grow long enough to produce seed; [for a plant] to spend its energy going to seed. The lettuce went to seed and we couldn’t eat it. Plants like that ought not to be allowed to go to seed.
2. and run to seed Fig. [for a lawn or a plant] to produce seeds because it has not had proper care. You’ve got to mow the grass. It’s going to seed. Don’t let the lawn go to seed. It looks so—seedy!
3. Fig. [for something] to decline in looks, status, or utility due to lack of care. (The same as run to seed.) This old coat is going to seed. Have to get a new one. The front of the house is going to seed. Let’s get it painted.

[my emphases]

For those who like visuals, here’s “gone to seed” illustrated.

#1: to grow long enough to produce seed

Broccoli raab. Each of these individual 4-petaled flowers will produce a seed pod containing six or more seeds.

Orient to the right hand edge of this mass. You should see a handful of immature seed pods against the straw in the background. Now look at the mass of seed pods.

An onion going to seed.

Butter crunch lettuce going to seed.

Giant red mustard. As with broccoli raab, each flower produces a seed pod.

See the thin pods along the stems and clustered at the bottom center of the photo? Each pod has almost a dozen seeds.

#3 below the fold– along with a bit of inspiration inspired by the giant red mustard.


#3: to decline in looks, status, or utility due to lack of care

The Bill of Rights

I let things go to seed all the time– love to watch volunteers come up! And of course, I save seed. This year I’m especially excited to harvest the mustard seed. Miss M expressed an interest in mustard seed earlier in the season. She asked how large mustard seeds were. I asked why she wanted to know. And she said that she and a school chum had been talking about mustard seeds and the bible. 

And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.