Let’s see if last year’s broccoli seeds are viable.
I was reading a story this week about a man that single
handedly planted a forest covering 1,360-acres. A little more than 30 years ago, a teenager
named Jadav "Molai" Payeng began burying seeds along a barren sandbar
near his birthplace in northern India's Assam region to grow a refuge for
wildlife. Seeds are magical things and this time of year it always amazes me
just what gardeners can get out of just a few packets of these living micro
organisms held in a state of suspended animation or dormancy.
I have mixed success with seeds, that’s probably the same in
nature and why some plants produce so many of them. There are many things that can affect the
viability of seeds, including moisture, air, temperature, and light. In an
ideal situation and environment, every single seed we planted would grow into a
seedling, but as we all know, that doesn’t normally happen.
Although dormant, seeds are still slowly using their food
reserves. Some have more in reserve than others and can lay dormant for years
before bursting into life when the right weather conditions appear. Small flower and vegetable seeds do
deteriorate over the year and that’s why tend to go out and buy a new packet of
broccoli seed every year instead of using the seeds from last year’s unopened
packet.
When the right weather conditions wake the seeds up they
begin to germinate and emerge from their hard seed coat. Here is a brief explanation
of how a seed wakes up and busts into life, just like us gardeners do when the
weather warms up.
There are four major
factors that are affect germination:
Moisture: A dormant seed only contains 10-15% of water
and is essentially dehydrated. The seed has to absorb water in order to become
active. It is taken in by the seed coat and enzymes in the seed become active
and they start using stored food reserves. The embryo then begins to swell and
the softened seed coat ruptures as the seed grows too big for its encasement
and germination has starts. The seed leaves or cotyledons now show but photosynthesis
doesn’t begin until the true leaves are developed and at this point in
development the seedling is still surviving on its own food reserves.
Air: In the dormant condition the seeds
respiratory rate is very low and so oxygen is required in very small quantities.
But for germination, oxygen is needed in large quantities. The seeds get oxygen
that is dissolved in water and from the air contained in the soil. If soil
conditions are too wet, an anaerobic condition persists, meaning that the seeds
are living without air so will hold back germinating until they feel the supply
of air will be constant. Aren’t they
clever?
Temperature: Germination can take place over a wide range
of temperature and is specific to individual crop types, and can be specific to
varieties. When I was growing seedlings in my polythene tunnel I had a hotbed
with heated cables. The cables were put at different depths under sand to
regulate how much heat each type of seedlings got, I did make life a bit
complicated for myself though as there is an optimum temperature for
plants. The optimum for most crops is
between 65-75°F and most seeds will germinate happily in this range. Exceptions do apply though, for example
lettuce germinates best at 65°F and can be held back at temperatures over 68°F while
peppers and aubergines prefer warmer
temperatures around 80°F and will not germinate well at cooler
temperatures. If your soil is too cold
or too hot, your seeds may not sprout. Check your seed packet to find the best
temperature needed for your seeds.
Light: Light has varied effects on germinating
seeds of different plants. Some seeds need light for germination, while in some
seeds germination is hindered by light. Most wild species of flowers and herbs
prefer darkness for germination and should be planted deep in the soil while
most modern vegetable crops prefer light or are not affected by it, and are
planted shallowly to allow small amounts of light to filter through the soil.
How deep to plant?
Seed size usually is a good indication of how deep to plant
your seeds, which usually corresponds to how much light they need. The general
rule of thumb is to plant your seed at least as deep as the seed is long.
Certain seeds need light to germinate and shouldn’t even be covered with any
soil! Check the back of the seed pack for specific information on how deep to
plant your seeds.
Why didn’t my seeds
germinate?
Have all the seeds failed? If this is the case, more than
likely it is an environmental condition. Seeding too deeply, planting in cold
soil, too much or too little water, improper soil preparation, and birds or
rodents are the most common causes for environmental conditions that prevent
seeds from germinating. When germination is poor it is most likely a
degradation of seed quality, and the seed has begun to die. In general seeds
hold high germination rates for 2-3 years but if the packets have been opened
the seed needs to be kept in airtight containers and not left in a damp shed
like my broccoli seeds have. I won’t be risking them this year
