Of course, plants need hardening off before moving from a greenhouse to the field. However, growing seedlings to transplant size (3”-4”) inside a greenhouse, and then moving them outside into light shade for a few days to harden off, has produced mixed results—many die in the field.
I have had much better success transplanting gooseberry seedlings that have been grown to size outdoors—seedlings are “woodier” and better survive transplanting into black plastic groundcover. Consequently, once in plug trays, seedlings spend only a couple of weeks in the greenhouse before moving outside.
A temporary bench for the seedlings is simple to set up. In the picture above, the bench top is a 4’ x 8’ sheet of plywood covered with plastic, on top of a raised bed. Trays rest on a capillary mat on top of the plastic sheet. Hoops—10’ lengths of 1/2” PVC pipe held in place by 1/2” rebar stakes—are used to support shade cloth.
Depending on the weather, the capillary mat frequently needs watering twice a day. Shade cloth is used only in the daytime, until seedlings adjust to the light; and often when it rains, to prevent rainfall from flushing media out of the cells. Uncovering seedlings in the evening helps with the initial hardening off.
This year I finished transplanting seedlings from flats to plug trays by April 1 and moved them outside 2½ weeks later. I began transplanting larger seedlings to the field May 1 and finished all seedlings by middle of the month.
T o hold them in place, each end of a hoop (1/2” PVC pipe) is slipped over a 2’ long piece of rebar driven into the ground. Shower curtain rings are handy for attaching shade cloth to hoops.