by Eric Soderholm, CFSA’s Organic Transition Coordinator

Transplants can provide you with a solid, earlier start in the garden as you face variable spring temperature and moisture conditions. They tend to be more robust and can potentially withstand greater pest pressure, as well. Here are a few basic tips I have picked up from farmers I’ve worked with regarding the care of tender transplants:


1.     Timing: Time your seeding schedule as best you can so that starts are at an appropriate maturity stage during the ideal window for transplanting that crop. It is best if plants are neither root bound nor too spindly when the time comes to set them out. It can be tempting to start seeds earlier than necessary. At times, this might be in your favor if temperatures are abnormally low and there is increased cloud cover as we’ve seen this spring, since these factors can seriously slow germination and growth. On the other side of the coin, delayed planting is sometimes inevitable if field conditions are too wet and turned-in cover crop residue needs additional time to break down. Transplants that are root bound can benefit from a shot of diluted fish emulsion or other liquid fertilizers to hold them over until they find their home in the field.


2.     Moisture: Be careful to water gently as too much water pressure can pack seeds deeper in the soil and make sprout emergence more difficult or injure delicate young plants.  Invest in a watering wand that makes an even, gentle stream or use a watering can with a similar ability. Avoid watering too late in the day so that seeds are not over moistened. Be sure to have proper ventilation, ideally with openings on either end of your transplant nursery structure, so that there is good air flow. This can help in reducing seed rot and other issues when the soil remains too moist during cloudy spells. Be aware of the drying patterns in your trays, as the edge cells/soil blocks will typically need a bit more water than those in an interior position.


3.     Temperature: Whether you are starting seeds in a passive solar greenhouse, caterpillar tunnel or a south-facing window of your home, moderating temperature is important so that injury from the extremes is avoided. Open ventilation pathways as appropriate in the morning on warm days and close in the late afternoon to capture built-up heat on cold evenings. For seeds that need an extra heat boost during germination, such as those in the nightshade family, consider using plastic covers or “domes” that double the greenhouse effect. Electric heating mats that set below transplant trays and warm the soil from beneath can be much more energy efficient than heating the air of the entire structure. Likewise, incorporating heat reservoir components, such as black-painted barrels (or buckets) filled with water, into the design of your nursery structure can make for big savings.


4.     Other Considerations: Try to control rodent populations in or near your nursery structure. They can be a problem with larger seeds, such as those in cucurbit family, which they dig up and eat. Avoid handling plants until transplanting time. They have enough hazards in reaching maturity already, so as enticing as it might be to run your hands over your little ones, do not touch them! They can be sensitive to oils and other substances you may have been on contact with and should be left alone. This is particularly true for those who smoke or otherwise handle tobacco products. Be sure to wash your hands thoroughly before handling plants and resist the urge to light up when setting plants out.


5.     Final Preparations: Try to reduce all potential forms of shock as your transplants are introduced to the field. Before you set out your plants, it is best to given them some time to acclimate to the outdoors. Allow a “hardening off” period of about one week or more before planting. Be observant of predicted conditions so your transplants don’t get injured by a frost, wind or heavy rain since at this point you can still move them back under cover if necessary. If possible, set plants out in the morning, late afternoon, or during cloudy weather to avoid heat shock. Ideally you should have your chosen irrigation system ready to set up immediately after you finish transplanting. Try to soak transplant trays before planting, this will make them easier to pop out of celled trays and give the plants more initial moisture. Ensure that plants go into the ground as soon as possible after removing them from trays to reduce drying out. It can be helpful to give plants a shot of liquid fertilizer, in some manner, immediately following transplants (by hand, through drip irrigation lines or mixed into the tanks of a tractor-drawn transplanter).