When to Move the Plants Out of the Starter Greenhouse?

The biggest advantage of starting plants in the greenhouse is that a greenhouse provides regulated temperature.


Seedlings often require a narrow temperature range to produce the best possible growth. The walls of the greenhouse also protect the seedlings from other elements of weather such as snow and rain.

greenhouse temperature
A greenhouse is often much warmer than the outside temperature, even when it does not have an artificial source of heat.

The clear ceiling of the greenhouse allows ultraviolet radiation to enter the greenhouse and the plastic material provides insulation, which keeps the heat from escaping the greenhouse.

This effect is most noticeable on a cold, clear day.


  • Keeping a greenhouse at the correct temperature for the starter plants requires frequent maintenance on the part of the gardener.
  • The temperature can be lowered by opening the doors and windows as well as installing fans to improve airflow.
  • The gardener can increase the temperature of the plants by covering the plants with a thin, insulated material known as a frost cover.
  • This material should be able to allow light to reach the plants while still keeping the plants warm.


vermiculite potting soilSoil is often an important factor in growing starter plants in the greenhouse.

These plants are typically grown in containers, so the ingredients in the growing medium can be mixed to exact proportions before it is needed.

Starter plants often require soil-less mediums such as vermiculite or peat moss until they reach a certain stage in their growth.

They may also need a specific type and amount of fertilizer.


plant irrigationThe amount of water to provide seedlings is also a critical factor in their development.

Insufficient water will prevent the plants from growing is fast as they should, while excessive water can cause the roots to rot.

The growing instructions for a particular plant often state that the soil should be kept moist but not wet.


greenhouse ventilationThe contained environment of a greenhouse can restrict the ventilation of the starter plants.

A greenhouse should always have some vents open to prevent the accumulation of oxygen, which can inhibit the plant’s growth.

The gardener must always consider the effect that ventilation will have on the temperature of the greenhouse.


cool climate gardening
Gardeners often grow plants in a greenhouse until they are hardy enough to grow outdoors.

This provides the plant additional growing time outside, which is most helpful when you are in a cool climate.

Gardeners typically start plants in a greenhouse in late winter so that they can be planted outside in early spring.


  • The ideal date for moving plants out of a greenhouse is often related to the last frost of the winter.
  • The unpredictability of weather can make this transplant date a challenge to determine.
  • Moving the plants too early in the year can result in the loss of that crop, while moving them too late can defeat the purpose of starting them in the greenhouse.
  • Plants that are started too early can also become root bound while waiting for the last frost of the year.
  • This means that the roots become tightly constrained by the planting container, which can make the transplant more difficult and less likely to ask succeed.
  • Gardeners often rely on almanacs, which provide the date of the last frost for previous years for a specific location.


greenhouse transplantThe transplant instructions for a particular plant generally provide the information needed to calculate the transplant day.

This includes the minimum amount of time that must pass between planting the seed and moving them outside.

The instruction should also provide the transplant date relative to the date of the last expected frost.

The gardener subtracts the number of days that the plant requires to mature from the last expected frost date to obtain the date the plant should be started in the greenhouse.


planting instructions
Assume for this example that the average date of the last expected frost in your area is historically March 21.

The planting instructions indicate that the plants should grow in the greenhouse for at least six weeks before moving them outside.

These plants should therefore be started in the greenhouse on approximately February 7.

Seedlings are often moved outside gradually.

They may be moved outside temporarily into a shady location during the day, and then moved back into the greenhouse at night.


The plants can be gradually moved to sunnier locations during the day for a week before keeping them outside overnight. This process allows the plants to become acclimated to the outside environment and is known as “hardening” the plants off.

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