This is a little note I was sharing with the community garden members where I currently garden, and I thought I would share it with you all as well . . . . 
In the garden, wherever I (and others) have used the compost produced by
 our garden, there have been a bunch of interesting seedlings.  At first
 I thought, hoped really, that they were chives.  They had that grass 
like look of young Allium seedlings.
But, no, what looked like a 
single seed leaf, divided into two long narrow seed leaves, very typical
 of the Umbelliferae family, but other than that I had no idea what they
 were.  They didn't really look like carrot seedlings, and I was hoping 
they were not hedge parsley, often called 'stick tights' or 'miners 
lice,' which spreads like wild fire.  It is totally edible and choice, 
by the way, but not many people know it or know how to use it.
Meanwhile, the seedlings have been coming in thicker and thicker.
Today I noticed a seed coat still posed on the end of one of the seed 
leaves.  I have been watching to see what the first true leaves look 
like in an attempt to identify it.  That seed coat looked amazingly like
 a fennel seed, so picked it off and tasted it.  Yep, fennel.  And it is
 coming in, in some places, as thick as turf grass.
The good news, is that 
fennel seedlings are totally edible in soup or salad.  They don't taste 
like much now, and they don't amount to much either.  But if you can 
tolerate them a few weeks, they will be yummy and tender.
  
I can tell you exactly why we have it in our compost.  Last 
year, I was waiting for the fennel seeds to become mature, and I was 
going to collect them for tea and flavoring--for myself and to possibly 
share with the food bank if people were interested.  But then right 
before they were mature, someone cut the fennel down.   And honestly, I 
did not investigate further.  But apparently they were put in the compost.
Fennel normally does not have this 
rampant kind of germination rate, at least not in California where most 
of my garden experience comes from.  Many kinds of seeds, especially but
 not exclusively those of the Umbelliferae family, have built in 
dormancy, so that only a few will germinate at any one time, staggering 
the germination of the seeds over days, months, and even years.  It is a
 built in survival mechanism, which allows at least some of the plants' 
off spring to survive all kinds of quirky weather changes.  Dormancy, 
however, is built into the seeds at the end of their development.  So, 
if you time it just right, by picking the seeds after they have 
developed viability, but before they have developed dormancy, you can 
end up with perfect germination as soon as everything else is in 
line--such as day length, moisture, and temperature.  Apparently, 
someone caught the fennel, in the exact perfect zone.  
For 
future reference, never ever put fully mature or nearly mature seed 
heads of any kind in the compost--unless you either want volunteers or 
you know for a fact that the compost is going to get hot enough to 
sterilize them.  Making truly hot sterilizing compost is an art and a 
science and it takes a careful blend of materials and attention and 
work.  Yes, it does sometimes happen by accident.  But don't count on 
it.
All gardens get volunteers.  Plants that show up, because 
the seed bearing parts rotted in place or in the compost. Some times the wind blows them in, or they arrive by birds, or perhaps even fairies.  Volunteers 
are one of the delights of gardening, as far as I am concerned.  I love 
surprises in the garden, and they are often superior to hybrids in taste
 and color, and nearly always superior to hybrids in vigor and 
hardiness.  Volunteers rock.  But not necessarily when they are coming in like turf 
grass . . . .
Gardening, of course, is a learning experience.  Community gardening is even more so.  We learn together in community.  We learn about gardening and garden materials management not just from our own experience, but from the experience of other gardeners as well.  We learn also, grace; to take the good with the bad and to turn sow's ears into silk purses, to turn a plethora of fennel seedlings into beautiful food.   
Nature abhors bare soil.  Sun light degrades soil nutrients in bare soil, and rain water dissolves them and washes them away.  In nature, if there is enough light, enough warmth, enough soil, enough moisture--the ground is always covered with either green growing things or with a deep natural mulch.  Nature attempts to do the same thing in the garden.  Nature gives us weeds and volunteers to save our soil.  It's our job, in the garden, to accept nature's innate system  and manage it to work in our favor . . .