Lars Lund

08 Sep 2020 14:34

Now it begins – the greenhouse in April

Outside it is spring, but inside the greenhouse it’s summer. The pests are awaking, and the plants do not get enough sunlight.

If you haven’t cleaned the house with lubricating soap, now is the time.

In the greenhouse, it is time to sow carrots, radish, leek and cabbage.

Choose summer carrots that you can sow directly in the soil to get an early harvest. Sowing depth: 0.4 to 0.8 inches. Distance between seeds: 0.8 to 1.2 inches.

You can also sow summer or winter carrots in milk cartons with soil and later cut the carton open to plant out the roots in the kitchen garden.

Leek is sowed in pots or polystyrene boxes with drainage. Fill the pot with soil and organic fertilizer, if not fertilized. Press the soil a bit and drip irrigate. Overseed and sprinkle a thin layer of sand on top. Cover with plastic until the seeds are germinating. Lift the plastic during the day for aeration.

There are both autumn leek and winter leek. Choose winter leek, then you will have vegetables when you miss them the most. Plant out in June, thereby the risk of carrot fly attacks is low. 

White cabbage, red cabbage, brussels sprouts, kale and savoy cabbage are suitable for pre cultivation in April. Cauliflowers already in February. Sowing depth: 0.8 to 1.2 inches. Lettuce can be sowed every third week. Overseed in a pot or a bed in the greenhouse and cover with sand. In the greenhouse lettuce get crispy if watered well.

Vine flourish with small almost invisible flowers and they do not flourish all at once. Usually they are easily pollinated by insects or the wind, but you can shake your vine in April to be sure of a good pollination.

Kiwi, apricot and peach are pollinated by insects. If there are no insects, you need to stand in for the bee and pollinate, by spreading pollen from flower to flower with a brush.


Change soil in the beds in the greenhouse. As in the kitchen garden, greenhouse soil needs crop rotation, otherwise, the plants will get sick. 

You will get the healthiest soil by during crop rotation every year. If you don’t have enough dark compost, you can mix soil from your kitchen garden with compost. You can also buy fertilized soil. Fill the soil in a growbag or directly in the bed. 

A 12 inches deep crop rotation is recommended at least every other year. 

If you haven’t already sowed tomatoes and cucumbers in your window, do it now, especially if the tomatoes should ripe in time. Remember when they germinate, they need as much sunlight as possible. Maybe you should purchase a LED light for the sprouts, they provide sound light and uses very little electricity. 

You can plant out tomatoes in mid-May, while cucumbers require a soil temperature of 23 degrees, which it will be in June. Cucumbers need warmth to germinate well. While sprouting they prefer up to 30 degrees. Tomatoes can manage by 18-23 degrees, but while germinating they need lots of sunlight and 14-18 degrees for a good flower formation.

Om Lars Lund

Lars Lund
Danish horticulturist and journalist
Lars Lund has for many years engaged in the garden and greenhouse. Lars has published many books about greenhouses, and he has participated in many Danish horticultural TV shows. He is a walking garden encyclopaedia, and he has answers for most basic cultivation questions – also the more ambitious ones.  

Get to know Lars Lund