The successful germination of seeds is one of the key requirements for growing a good
crop of vegetables in a garden. But it’s not always a simple task to ensure that good
germination will actually happen, or to determine the reasons why seeds didn’t germinate as
expected. Sometimes when seeds don't germinate, it's possible to simply resow with a new batch
of seeds, or to fill in any gaps in germination with another crop, but sometimes poor germination
can lead to a loss of a crop, or to have less than was expected, especially with the time
sensitive fast growing crops that I try to squeeze into the gardens before the space
is needed for the main crop of the season. And with experience I have become more successful
at ensuring decent germination of a wide range of different vegetables seeds, in different
conditions, though I still struggle at times, and that can be frustrating. And I had an
interesting example of inconsistent germination of a range of different vegetables in my larger
polytunnel this spring, and it took me a while to figure out what was actually going on.
The beds in this protected growing space had been empty over the winter and I had planned
to sow a range of fast-growing spring crops in February and March. I sowed 10 different
crops at the same time in a single long bed, with a few weeks between sowing each of 4
bed in the polytunnel in order to have a staggered succession of these crops later in the spring.
While a few of the crops were transplanted into the bed, most of vegetable seeds were
sown directly into the layer of compost that we had covered the surface of the beds with,
as part of the strategy of reducing the cultivation or avoiding digging the soil. Because of
the cold temperatures that we had earlier in the spring, the germination of the first
few beds was delayed, but after a few weeks it became obvious that there was inconsistent
germination in patches along the rows of seedlings within all of the beds. I knew this wasn’t
an issue with poor seed quality, as all of the different types of vegetables were affected,
and the same seeds had produced good germination in the other gardens. I also ruled out the
possibility of slugs or some other pests eating the seedlings as they germinated, as this
polytunnel is largely free of slugs, and there wasn’t the tell tale sign of the stub of
the seedling stem left behind. I wasn't sure if the colder weather over a few week period
would have been that much of an issue, as even some of the later sowings had the same
issues of poor germination when it was actually quite a bit warmer. And I had really good
germination last year in this polytunnel with similar crops, using the same bed preparation
method, so I think the different watering method that I use this year was probably the
most likely cause of this inconsistent germination.
Last year I watered the direct sown crops by hand, using two watering cans filled from
a large water tank to evenly water the surface of all the beds. But this year I relied more
on the overhead sprinkler system that I had recently installed in order to reduce the
amount of effort and time needed to keep the soil sufficiently moist for the seeds and
young plants. There has been a temporary issue with this sprinkler system because of
the low water pressure that we currently have to deal with, and until this is fixed with
a new section of pipe, the pressure is quite low and can actually vary quite a bit depending
on if other people using the supply. I figured that this would probably be okay, because
I was able to adjust the system so that all of the polytunnel was watered even with low
pressure, and I was topping up with occasional hand watering of all the beds as well. But
this wasn’t enough, as it became apparent that parts of the beds were drying out faster
than others, with a patchy pattern of wet and dry areas becoming visible within a few
hours after watering with the sprinklers. And these drier areas coincided with the
areas of poor or no germination of the seeds. This was disappointing because I thought it
would’ve been okay with the two different methods of watering that I had used, and it
wasn’t immediately obvious to me why this had failed.
I think one of the key issues was the quality of the compost that I had recently added as
a thick layer onto the surface of the beds. This compost was part of a large load of bulk compost
that we had purchased, made mostly out of shredded wood and other landscape waste. I
had use the compost from this supplier before but this batch seemed a bit fresher, and not
quite so decomposed, or at least had not had a chance to mature as much. If I had put
this compost on the garden beds last autumn there would have been a chance for it to settle
in and continue to decompose on the surface of the soil. But I didn't allow the time
for this to happen, as the seeds were sown in the beds shortly after the compost was
added, and because we had added such a thick layer of compost, most of the seeds were positioned
in the layer of compost itself, instead of in the soil underneath. And any seeds in those
dry sections either didn’t get enough water to germinate, with some of them germinating
later when conditions improved, or they germinated and then dried up and died before they had
a chance to appear above the surface. I imagine the relatively loose and dark compost on the
surface dried out very quickly with the heat of the sun on a few of the warm sunny days
that we did have. And because the compost wasn’t firmly pressed into the soil or hadn’t
settled into place, there wasn’t the close connection between the particles or small
pieces of the compost to enable the water to move through the compost with capillary
action to bring more moisture up from deeper in the soil, similar to how a sponge or cloth
can become fully wet even if only part of it is immersed in water. I imagine this was
made worse by the fact that the individual particles of compost would have shrunk as
they dried creating an even looser granular material that was less likely to maintain
that essential capillary action.
So the low and variable pressure of the water caused inconsistent coverage with the sprinklers
which meant that some of the areas of the compost ended up drying out faster than the
others. But I still wondered why the hand watering that I had done to prevent this from
happening, wasn’t enough. When I scraped back some of the compost in different sections
of the bed to try to figure out what was going on I noticed that even after watering with
the watering cans there was a layer of really dry compost underneath a thin wet layer on
the surface. It seems that the dry patches were hydrophobic, actually repelling the water
or preventing the water from flowing down into the compost, and even though I watered
these areas the moisture wasn’t consistently getting down into these sections of the compost. It
seems that the way that I was hand watering was actually part of the problem. I had been
filling to watering cans and drenching the soil with a fair amount of water in a fairly
short period of time. And in the sections of the bed that had really dry compost underneath
this water was pooling on the surface rather than filtering down and most likely moving
horizontally to some place were a crack or section of moist compost enabled it to drain
away deeper into the soil below. So even though I was adding a fair amount of water,
most of it was flowing away from or around these dry patches every time I watered. And
the thin layer of moist compost on the surface dried out very quickly adding to the problem.
I realised that instead of drenching small sections of the beds at one time, I needed
to shift to a process of watering lightly, and repeating multiple times even if the same
amount of water was added in the end. So instead of a sudden downpour that would flow away
without wetting part of the compost, I needed to water lightly in layers that would allow
the water to seep down slowly so that there was a better chance of these dry patches underneath
would get re-moistened. Essentially I needed to do a lot more walking back and forth up
and down the rows between the beds when I was watering by hand. But instead I had been
trying to save time and to be efficient with the task so that I can get on with work in
the other gardens. If I had done this from the beginning, there might not have been such
an issue, but because I had let areas dry out quite significantly, it took quite a bit
of time and a regular light watering in order to re-moisten all of the compost.
So the simple reason for this inconsistent germination is that I didn’t water enough,
or I watered in an inappropriate way for the contact. But as usual, it's a bit more complex
than that, because if any of a number of other factors had been different, this issue perhaps
might not have occurred. If the compost had been more mature, or if it had been added
to the surface of the soil last autumn and kept moist over the winter, and had a chance
to settle in, then I think the risk of dry patches forming would have been reduced. And
I wonder if it would have been better for the compost to have been pressed or firmed
in after sowing the seeds, to establish better capillary flow, rather than being so loose.
Of course if I had fixed the water pressure issue earlier in the season then the sprinklers
would’ve been much more effective distributing the water more evenly across the entire area
of the garden. This would have significantly reduced the potential dry areas and the work
I needed to do to top it up with hand watering. And having those sunny days at a critical time
in the germination of the seeds definitely didn’t help. but I should have been much
more attentive to how quickly the compost was drying out in the sun. If I had watered
differently by hand with lighter layers rather than dumping a lot of water at one time, this
would have helped. And from now on I will definitely be watching out for water pooling
on the surface rather than flowing down, as this is obviously a sign that the compost
or soil underneath may have become hydrophobic, and may need some extra attention to remoisten.
In the end I did get a decent harvest of early spring or hunger gap crops from this polytunnel,
though the yield and the consistency wasn’t as good as it could have been if any one of
these factors had been slightly different. But that seems to be the case with so much of
what happens in the gardens, and an experience like this is part of the learning process
that it seems that I am and most other growers have to go through in order to be able to
consistently produce lots of high-quality vegetables year after year, especially if
we keep changing how we do things.