Transplant timing decision & Hardening off

Hardening off tomato transplants near house wall

Betting on when the last spring frost date has past isn't your only gamble in transplanting warm weather tomatoes, peppers, eggplants, etc. These plants are also sensitive to cool night temperatures above freezing but lower than 50 degrees F.

This week with temperatures in the eighties and nights in the fifties F has made it appear that summer has arrived and we're in the clear for transplanting. A closer look at next week's forecast reveals several days of night temperatures expected to be in the mid forties F. Such fluctuations are typical in high elevation, semiarid climates like ours.

Cool nights slow growth  for warm weather plants and recovery takes days. This knocks time off your growing season and raises the question about waiting until night temperatures are consistently warm. I choose to keep plants actively growing by keeping plants indoors and plan to transplant later in the month. Of course if you transplant plants into water walls to raise night temperatures transplanting is a viable option.

Whenever you decide to transplant, do harden off plants by moving them outdoors on warm days and indoors at night. Place where protected and shaded to minimize winds and UV exposure until plants can toughen and develop self-protection against chlorophyll breakdown from UV rays. A location near a house wall under eaves or on a covered porch is fine. A week of hardening off to acclimate transplants to the outdoor environment is usually sufficient.

Photo credit: Hardening off tomato transplants - Carl Wilson

Holding transplants

• With forty degree nights, growers are in a balancing act between how long transplants of very tender vegetables can be held versus planting and knowing they will be set back by the cold.
  
  Many transplants may be running out of nitrogen as seen on the tomatoes in the top of this photo. These plants are starting to come back with addition of a soluble nitrogen fertilizer when watering. A product that also contains phosphorous is useful to avoid the purple backs of leaves seen with phosphorous deficiency. The tray of plants at the bottom of the photo received regular fertilization.
  
  Don't apply too much fertilizer or you will end up with lanky growth. Of course these plants could be bumped up to pots larger than the 4 inch ones they are in but that is hardly desireable considering planting can hopefully be done in a week or so once nights are at least above 50, preferably 55 degrees F.
  
  What can be done in the meantime while waiting for warmer nights?


• Harden off plants by moving them outdoors on suitably warm days and back in at night.
  


• If tramsplants are very tender cover them with floating row cover fabric while outside. This should prevent sunscalding until they've adjusted to higher light intensity and have hardened off.
  


• Maintain enough fertility to keep transplants growing and leaves from turning yellow.
  


• Remeber that transplants set out too early or transplants running out of fertilizer require recovery time which adds to the days to harvest time.



• Keep blossoms pinched from plants. Now is not the time to set fruit as you want to keep them in vegetative growth, not flowering/fruiting growth.



• Watch the weather forecasts for when night temperatures are predicted to be 50 degrees F or higher.



• Transplant tender (not the very tender) transplants such as cucumber and summer squash that tolerate cool nights as long they are above freezing. Remaining cool season vegetable transplants such as chard, beets, romaine lettuce that will hold up better in summer heat, cauliflower, etc. can be put out (photo).



• Finish any soil prep such as compost additions and build new beds while weather is cool to work.

Photo credit: Held tomato transplants, Planting cabbage, romaine lettuce, Swiss chard - Both Carl Wilson

Spring weather - hardening off transplants and bees

Two things have been frustrating about our spring weather. It’s been hard to put transplants outdoors to harden off. The days when temperatures have been over 55 degrees F or that winds haven’t blown have been few. Exposure to the outdoors helps leaves toughen and some plant movement thickens stems.

Note that there is a marked difference between the light intensity outdoors versus near a window indoors, as much as a hundred fold increase. The plants in the photo went from low indoor light to bright sun. They should have been placed in the shade outdoors as an in-between step. Even outdoor shade is considerably brighter than indoor light. The plants reacted to the bright light by turning white, indicating a breakdown of green chlorophyll (photo-oxidation). Gradually acclimating plants to brighter light is another reason to “harden-off” plants in stages lasting only an hour or two – if the weather allows.

Then there is the poor honey bee. They have gotten off to a rough start. Fall conditions were poor for them to set up stores for surviving the winter. Bloom was late this spring and though it is abundant now, the weather has usually been too cool for foraging. All and all this has been a stressful time for colonies and predictions are that many probably starved out.

In addition to weather, there is the worrisome problem of colony collapse disorder. Nationally, initial results from a survey by the USDA Agricultural Research Service and Apiary Inspectors of America show managed honey bee colony losses of 33.8 percent over the winter. Last year losses were 29 percent. These continued high losses are causing fears of poor crop pollination. Gardeners can do their part by planting bee-attractive flowers and avoiding the use of pesticides particularly during bloom periods when bees are active.

Photo credits: Solarization of tomato, Carl Wilson and Honey bee, Jack Dykinga