Germination & Seed Depth Greenhouse

Objective  Analyze the effects of planting depth in relation to seed germination.

Quick Review  Propagation - Also defined as the reproduction of plants  The most common methods is through seeds  Germination - The beginning of growth from a seed  Germination Rate - The percentage of seeds capable of germinating

Indirect Seeding  A process in which the seed is sown in a place separate from where the plants will eventually grow to maturity.  The seedlings are transplanted one or more times before reaching the permanent growing area.

Sowing Seeds  Tomato:  Time to Seed – 4 to 6 weeks before transplant date  Germination time in days – 7 to 14 days  Planting requirements – cover seed ¼ inch  Germination Temp. – 70 to 80 degrees F

Planting Seeds  planting depth is a key factor in successful germination.  Seeds planted too deeply will likely rot before they germinate  seeds planted too close to the surface will dry out, and produce spindly growth.  Some seeds need to be sown at or near the surface to allow exposure to sunlight, or they will refuse to germinate.

Depth of Planting  The most common cause of poor germination is the depth at which the seeds are sown.  Small seeds should be planted on the soil surface and pressed or rolled in for best results  They contain only enough stored food for a limited period of growth.  If the seedling is to survive it must emerge from the soil and quickly begin to produce its own food.

Depth of Planting  If seeds are too deeply buried beneath the soil surface, the seedling will either…  exhaust its food reserve prior to reaching the soil surface causing its death OR  lack of sufficient oxygen will prohibit germination altogether.

Conditions for Germination  1) Water is needed to:  Activate hormones and enzymes  Swelling of the seeds = bursting of seed coat.  Transport of simple materials to the embryo – to be used for respiration and growth.  Metabolic and enzyme actions – occur in solution, therefore need water.  Conversion of storage compounds into simple components (i.e. starch to glucose)

Conditions for Germination  2) Oxygen is needed for aerobic respiration.  Without a supply of oxygen, seeds fail to germinate because of the lack of energy – in the form of ATP.

Conditions for Germination  3) Suitable temperature  All reactions (in germination) are controlled by enzymes.  Optimal temperature for enzyme activity leads to faster rate of germination.  Freezing = inactivates enzymes  Very high temperatures = denatures enzymes

Seed Size and Planting Depth  Food for the seedling is stored within the seed; this is the edible part of plants we eat such as rice, wheat and corn.  The smaller the seed, the smaller the reserves of food and the less energy the growing plant has to push up to the surface. So smaller seeds need to be planted at shallower depths.  For instance, carrot seeds are less than one- eighth of an inch long and should be planted about one-quarter inch deep.  Corn seeds, thick, packed with food and over one-quarter inch long, can be planted as deep as 4 inches, though 2 inches or less is better

Sunlight  The more soil that covers a seed, the less light it receives. Now, for some seeds, this is a good thing. They won't germinate in the light, requiring total darkness to begin the process. Others need light and won't germinate if they are buried by even a quarter inch of soil. Luckily, most seeds are less picky about light. Always follow the directions on your seed packet, especially if the instructions include details such as "press into the soil lightly and do not cover," indicating that the seeds need light to germinate.

Let’s Germinate!  Plant tomato seeds at various soil depths  Surface  Normal  Deep Hypothesize the results of the plantings.