Propagation

Propagation is one of the most important aspects of a successful agricultural endeavor. A grower must decide whether to direct seed or transplant a crop. All root crops or ones that have taproots are usually direct seeded while others are commonly transplanted in smaller operations. At the Chadwick, or Up-, Garden at UCSC about 80-85% of the crops are transplanted, a practice that can be used to extend the growing season and ensure a specific crop density in the beds. However, transplants require the additional costs of building and maintaining a greenhouse facility and the extra labor that goes into the process of transplanting. Typically, two different types of trays are used: wooden flats and plug trays (often the Speedling brand). Each method has its own pros and cons. Wooden flats fit many more plants in a small area but require more skill for transplanting and starts can also be kept for a longer period of time in wooden flats before transplanting if environmental conditions are not favorable to transplanting (8 or 9 weeks). Starts from plug trays are much easier to transplant but with limited nutrients the starts must be transplanted within 5 to 6 weeks after planting. Furthermore, there are compaction issues as the soil begins to lose pore space and nutrients. Some varieties of plants simply grow better in one type of tray while others do well in both. The Up-Garden uses more flats in the spring and more plug trays in the summer. Starts can generally be transplanted once they have 6 to 8 leaves but before doing so trays are placed on outside benches for a few days to strengthen cell walls with wind movement and to “harden them off” to the conditions outdoors. This will minimize transplant shock and ensure successful transplanting.

One of the most important aspects of propagation for starts is the potting mixture used in the plug trays or wooden flats. The soil media must physically anchor the plant and provide adequate drainage properties to reduce fungal disease but retain moisture and encourage gas exchange in the pore space. Furthermore, when growing in a greenhouse, the environment is incredibly conducive to growth of all kinds, including diseases and pests. For this reason, some propagators believe in using a sterile mix; simply heating soil to 130ºF for at least 4 hours should kill all of the detrimental seeds, pathogens, pests and diseases but still maintain some beneficials while if the soil reaches around 180/190ºF it is pretty much sterile and not biologically active. At the CASFS farm, they believe in biologically active soil mixtures and are conscientious about trying to utilize local and renewable components. Peat moss is quite common in potting mixes but it is a slow growing resource in the Northern latitudes that is being quickly degraded. Their mixture is primarily soil and compost based, but it includes coconut husks, vermiculite, leaf mold (leaf compost), perlite, sand and sometimes fish, blood or bone meal.

In controlling for pests, pathogens and diseases, it is important to keep greenhouses clean, encourage good air flow through the site, avoid contamination, deal with any outbreaks quickly and aim for idealized soil structure, which is 50% air by volume. Roots grow in the pore space (air content) of soil so it is important that soil structure supports good, even pore space. This pore space should be 50% water and 50% air.