Seeds

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