Propagation/Greenhouse Management
Part 1 – 104 | Unit 1.3
Lecture 1: Seed Biology, Germination, & Development
- Producing seedlings ready for transplant can take as little as two weeks for fast-growing
crops such as lettuce and brassicas grown in small cells under optimal environmental
conditions, and up to ten weeks or more for slower-growing species such as peppers, and
alliums grown under less than perfect conditions or when producing larger transplants for
field production
The process of cycling plants from your most precise environmental control during
germination and early development, through seedling maturation and the process of
hardening off will be explained in greater detail in Lecture 2
D. Qualities/Characteristics of Seedlings Ready for Transplanting
- Seedlings ready for transplant ideally should have:
a) A root system and root knit sufficient to hold together soil surrounding the roots
b) At least two sets of well-developed true leaves, true to color for the species
c) Cycled through the process of “hardening off,” whereby seedlings have been exposed to
outdoor conditions similar to their eventual in-ground growing environment for at least
several days, including full exposure to day-night temperature fluctuations to help build
carbohydrate reserves, and full exposure to the wind and sun to strengthen cell walls
and enhance tolerance to future the extremes in growing conditions
- Holding: Maintaining seedling quality when transplanting is delayed
a) At times, transplanting may be delayed and it may not be possible to transplant
seedlings when they are at their optimal stage of development. This could occur:
i. When excessive rains prevent cultivating and preparing the soil
ii. When inadequate rain means it is too dry to prepare the soil without degrading soil
structure and you must wait for rain or pre-irrigate
iii. In cases of succession planting, when the ground for your new seedlings is still
occupied by a crop that has not yet matured
iv. When you are unable to prioritize new plantings due to other seasonal demands
b) There are several ways to keep your plants in good condition until you are ready to
transplant:
i. Know which crops tolerate holding and delays in planting and which do not. For
those that do not hold well, prioritize their planting whenever possible:
- Cucurbits, heading brassicas, bulbing onions, and peppers, for example, typically
do not respond well to holding - Leeks, tomatoes, collards, and kale are all crops that can be held well, both
responding to holding strategies and rebounding well once transplanted
ii. Provide supplemental fertility to compensate for the nutrients that may no longer
be available in your soil mix. As seedlings use up available nutrients, growth will
invariably slow—supplemental fertility can address this issue.
iii. Move seedlings into a cooler location or microclimate to slow the rate of growth
iv. Move seedlings into partial shade to reduce photosynthesis and slow growth.
Note that plants may need to be hardened off again if they are held in shade for an
extended period in order to prepare them for garden and field conditions.