Organic Greenhouse Clean-out.

Before you clean out your green house this year, please consider the following; there is a very simply procedure to follow for all organic growing areas that will greatly reduce your pest pressure and input of bio-controls in the following season/cycle. This is essential, whether you have 200 acreas or 10 square feet.


The time has come. Plants are removed, heat is reduced the days are short, and just when you hoped for a break, you remember the hours of clean-up required to prep for next season. But don’t be fooled. While you are ridding the area of plant material and old growing media many of the bugs that were in your house will persist. In most cases, mites and insects will be triggered into diapause (insect hibernation) by low light, low temperature or some combination of both. Because so many plants die in the winter or drop their leaves, similarly, many insects have evolved to take to the ground to over-winter.

For example: two spotted spider mite, sensing cooler temps and low light will turn bright red in colour, slow down, and make their way deep into the ground below. They will not penetrate concrete, but will follow drains, heat pipes, pillars and anything else. They will find tears and gaps in plastic and get underneath.

Two spotted spidermite about to diapause and turning red
normal spidermite and eggs

When heat is turned on in the spring, or the light levels increase, many of these insects will return. It is common to find spider mites return to the corner of the house they were particularly bad the year before.

Fortunately, many of the good bugs follow the same behaviour. Some above ground mites will follow the spider mites, eat a few and diapause in the same manner. Some soil mites rely on this seasonal migration and thus their diapause is several weeks later so as to take advantage of the influx of food. You must take advantage of this natural cycle.

So, here is what you need to do at clean-out.

  1. Clean your house. (It sounds simple, but it’s not. The level of cleanliness I will not suggest as I know that the tidiest growers, with spotless floors all year, and a clean-out that sparkles have the same mold/mildew and pest pressure as those who leave the floor a mess. So clean-up as you see fit, or as your own experience suggests).
  2. Avoid using any soaps or detergents and certainly no herbicides, pesticides or fungicides.
  3. Apply stratiolaelaps scimitus to the floor. If you’re already on the ball, these predatory mites were in each pot all year. But as you have thrown out the pots, you’ll need more stratiolaelaps. This time, sprinkle the carrier and mites directly onto your floor. Put extra amounts near heating pipes or anything thing that penetrates the floor (pillars, plumbing..etc) These will eat overwintering spider mites, thrips, and most everything else in the soil before diapause.

Now, here is what to do before start-up.

  1. Grow several beans in a few pots and repeat this every week for 3-5 weeks. (strike is the best variety for this). These will be trap plants so they don’t need to be pretty.
  2. Once beans are large and sturdy, place a pot in the middle of the house or area. Monitor.
  3. Any mottling on the leaves or webbing indicates spider mite. Remove this plant and replace when the next plant is ready. You are literally “sponging-out” the spider mite.
  4. As heat and light increase, be ready to replace bean plants regularly.
  5. When plants remain clean, your house is ready!

Clean-out jpeg

That’s all you need to do. It is not labour-intensive and it is certainly inexpensive. Remember you can get fresh, overnight, stratiolaelaps for as little as $0.50 per square meter. Most growers using this technique are putting 5-10 beans in pots from 6” to 11” in diameter, and only a few pots per clean out. In large houses they may do one bean pot per row. By the second year using this technique most growers are only needing to replace their plants twice.

But wait, there’s more! If you have kept to a great organic pest management program, you will reap many other benefits from a non-chemical clean-up:

  1. Aphidoletes aphidimyza senses low light, eats a considerably greater amount of aphids and take to the ground to overwinter as pupae. When light and heat return in the spring, they too will re-emerge – giving you a free head-start. (aphidoletes diapause with less than 14 hours of light. The smallest amount of light (like a string of led Christmas lights or a solar walkway light is enough to delay this reaction.)
  2. Native Aphidius (wasps that parasitize aphids) will return early in the spring.
  3. All soil pests will be met with high levels of stratiolaelaps.
  4. Native whitefly species that can overwinter on dead plant material will have been consumed.
  5. Natural molds, and fungi will be plentiful, thus occupying space for more damaging molds and fungi to take a strong-hold.
  6. Beetles, like delphastus and stethorus will re-emerge from diapause as adults.
  7. Brown-lacewing, which does not slow down until below 4 degrees celsius (if applied the year before) will have remained in your house and cleaned up anything on the surfaces.
  8. Amblysieus fallacis will return to your new plants almost immediately, and if not they are likely on your plants outside the house creating a buffer against spider mites.

Good luck, and happy clean-out. If you’re wondering how this clean-out fits into the greater picture. Take a look at the bio-control program pictures below.


Initial plantings:

small plant on bench jpeg

During normal growth:

medium plant on bench jpeg

Changes in weather, and other variables may mean the preventative rates were overcome. Consider this as plants are large and a problem becomes evident.

large plant on bench jpeg






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