Season Extension: Moving Your Structure

A significant part of season extension involves moving an intact structure.

This basically allows you to get two (or possibly three) plots of production from one investment.

The idea is to start a relatively cold tolerant crop very early in the season (the timing will be different in different locations).

  1. Once the crop is firmly established in location A, (and it has warmed up) you will move the structure to location B and start another crop.
  2. You will harvest the crop in location A and then after working the soil, plant another crop in location A which is intended for fall harvesting.
  3. After location B is harvested and before frost you will move the structure back to A.
  4. Instead of doing twice in location A you could also choose location C.

A structure can be equipped with wheels which will run over the soil. There is quite a bit of flexibility where you go and the terrain you navigate.

The structure can be equipped with rollers on a track. This will determine where you go and this is usually intended for moving a bigger structure with fewer people.

The most common method of moving is sliding the structure on the soil. The base rail can be wood or steel.

It is critically import to understand the logistics of moving on a structure before you start. It is not hard to move a structure but it is also not hard to do damage.

Having a plan for proper anchoring is very important for a movable structure. Your structure is at a vulnerable state when you release the anchors. Once you start, the job must be completed quickly. You have to be aware that the anchors may not come out or go back in easily so you may need to give yourself some extra time.

One other area of consideration on a movable structure is the ends. There must be some sort of a flap or vent along the bottom so that when a structure is being moved, the ends will not uproot plant material. Generally speaking to have this ability in the ends takes away from the structural integrity, so some extra anchoring may be required.

You can see more information and photos on our movable information page. Please don’t hesitate to call us with ANY questions you may have. This can be a very useful addition to your structure, but must be understood correctly.

Season Extension: Hanley Caterpillar Tunnels

The first area to discuss regarding season extension are those structures that are simple enough to disassemble and relocate to another spot-primarily referring to Hanley Caterpillar Tunnels.

The real lure of these buildings is their low cost and simplicity to move. Generally the area is prepared in advance and then the tunnel is moved over the area when the planting is to be done.

Since the original design specified 6′ hoop spacing, the intent was always to remove the cover before risk of heavier snow fall. More often now, growers are going to 5′ spacing (and sometimes 4′) to allow the covers to remain on longer or even permanently.

By having a smaller hoop spacing, it allows the cover to stay on permanently, which allows for a much earlier start in the spring.

The key to the concept of the Hanley working is in the rope.

  • The back and forth pattern of the rope resembles the way a person would lace up a boot.
  • Typically there is a spring loaded clip at the base where the rope passes through.
  • Once the rope is fully installed, it is important to tighten it through three passes from end to end.
  • If the rope is not tight enough, the wind will create wiggle and movement sideways.
  • When the plastic is tight enough, it also allows the grower to slide the plastic up the hoop to allow ventilation.

Generally the plastic is about 25′ longer then the tunnel.
This allows the installer to bunch up (pig tail style) the extra poly at both ends between a pair of posts.
It is important to get the plastic as tight as possible lengthwise first.
There must also be a rope from the top of the last hoop to the tie off post.

There are a couple of challenges to consider with the hanley tunnels.

  1. One of these challenges is to create a proper entrance. Typically entrance is achieved by slightly lifting the plastic and ducking underneath.
  2. The other are of challenge is the low shoulder height of the structure. This restricts the use to a couple rows of taller items in the middle and a couple rows of shorter plants along the side. The width of the tunnel does lend itself to three regular size beds.

Once you have learned about the nuances of the hanley tunnels, and asked any questions that come up, you will be better prepared to have these efficient season extenders work for you and your application.

Feel free to look at our Hanley Application page for more information and photos, and give us a call with anything else you require.

We are pleased to have many happy customers these structures are working for, and look forward to you being next!

Check out our new book if you want to know more “So You Want to Buy a Greenhouse…Your Guide to Planning a Greenhouse Purchase”

What is and isn’t “proper ventilation”?

Proper ventilation, in a nutshell, equals adequate air changes and movement while maintaining adequate light levels and humidity in a given area. Proper ventilation is about proper balance.

The challenging part of achieving this balance is that there is such a wide range of requirements for different plants. It is important to identify what is ideal for each variety that you are growing. It will not be feasible to have a perfect climate for each variety of plant, but you really should avoid grouping together plants with a wide difference in requirements. That would simply ensure that you are not doing very little properly.

Putting shade cloth over a greenhouse may lower the temperature to an acceptable level for your plants but that does not equal good ventilation. You may be depriving the plants of their critical light requirement plus you are not doing anything to enhance air movement.

Turning on an exhaust fan may create the required amount of air changes or movement, but with a temperature far below the plant optimum, your plants still will not achieve their potential. Fans also draw air in a straight line from intake to exhaust. This does not address “stagnant corners”.

Many times, light equals heat. They go up together and go down together. It is important to understand how and why they are controlled differently and where the overlap on that control is.

Generally speaking, proper air changes equals one air change per minute. Some plants require more and some can get by with less. For this, you will need to know what the air volume is for your building. It is a little trickier to calculate this on a gothic or quonset shaped structure. Using the length x width x 80% of peak height will give you a close enough number in either cubic feet or cubic metres.

With the next 4 posts we hope to create a more thorough understanding of how to achieve a good environment for your plants. This information will be helpful as to research options so that you can balance costs with benefits and return. Especially in the area of ventilation, many times expenses associated with proper ventilation will be offset by exponentially higher returns.

Air Circulation & Humidity Control

Even though many people would consider air circulation and humidity control as totally separate functions, they are closely intertwined.

You may have the proper sized openings to create the proper amount of air changes.

You could still have hot or cold spots in your greenhouse if you do not have proper circulation.

The same can be said about removing humidity.

For a ventilation system to have optimum efficiency and benefit, there must be balance. Having proper air circulation allows you to achieve that balance.

Horizontal air flow (HAF) fans typically come with a cage around the blades, a hanger bracket and a cord with plug. This allows them to be attached or suspended from the frame at the proper location. The motors are rarely more than 1/3 hp.

HAF fans always are installed in pairs and blow in opposite directions. A short greenhouse will have one in the front right corner and in the back left corner. A longer greenhouse will still have one in the front right and back left but also two half way down the length. The one on the right will blow in the same direction as the front right. The one on the left will be blowing in the same direction as the back left.

HAF fans should never be mounted in such a way that allows them to be blowing directly at plants. This would create an uneven drying. Some people will aim the fans slightly in the direction of the cover to ensure maximum air flow along the cover to maintain dry covers.

These fans run continuously to ensure that the temperature and humidity are spread evenly throughout. It also ensures that your thermostat or humidistat are reacting to air or moisture that is representative of what is going on in the greenhouse.

Ventilation is a difficult area of greenhouse production to get perfect. The more attention you pay to the details and modify what you are doing, the greater your production. The tricky part is that with all the variables, no two years will be the same. Carefully consider all your options and the situation you’re dealing with and you will have success!

The Variations of Passive Venting

In a nutshell, passive venting is creating an opening and letting the warm / hot air escape. The simplest form of this is opening a door or window. Just because it is simple does not mean that this method will be effective in cooling your greenhouse.

If your ends face into the prevailing winds, if you can make your doors big enough and if your greenhouse is short enough. That is a lot of “if’s” and you will still be doing a lot of running back and forth to have the correct amount of opening for the amount of ventilating you need to do.

We have already reviewed the most common form of passive ventilation in the roll up sides. It was noted that roll up sides work much better when paired with a high opening to create a chimney effect. It is a fact that hot air rises so the higher you can create an opening, the more effective it will be.

If you are relying solely on gable end windows, either motorized or manual, they will need to be quite large. You will also need to have the benefit of a regularly strong prevailing wind.

The most effective form of passive venting is a continuous roof vent. This will provide a continuous opening in the precise area where the air is the hottest. A roof vent should always be mounted down wind of the prevailing wind. The benefit of being down wind is that the wind creates a vacuum as it goes over the greenhouse and sucks the warm air out.  The air intake for a roof vent is often a roll up side.

A significant down side of a roof vent is the up-front cost. The cost is the same for a narrow and a wider structure. This is the reason they are almost exclusively put on wider buildings. The cost is simply spread out over a bigger area. The effectiveness of a roof vent still makes it appealing in spite of the cost.

Roof vents can be controlled manually with a chain fall opener or with a motorized gearbox. A motorized system can be a simple open / close controller that you set the limit switches or it can have a proportional controller that allows for pre-set stages. It is with an automatic controller that the benefit of the roof vent will really become apparent. Every couple of minutes it will react and adjust to the inside condition of the greenhouse.

All of the expenditures involved with your greenhouse need to be weighed as a cost versus benefit or cost versus return. This process is especially challenging when considering the options of ventilation. Many of the expenses are subtle and hard to measure. The returns are equally hard to quantify since weather is an additional variable. This makes it even more important to keep accurate records and be aware of your options for improvements.

Installing Wire Insert on Multiple Layers of Plastic

In response to a few questions about increased difficulty of installing the wire insert on 3 layers of 7.2 mil plastic. I have done my experiment with zero added degree of difficulty.

I don’t want to leave it just like that. I would like to add a few points.

First of all, the temperature was about 18C when I did this. It will progressively get more difficult because the plastic is less pliable as the temperature gets colder.

I should follow this up with the same experiment when the temperature is below freezing.

For my experiment I put extra screws into the channel simply to increase the chances of interference between wire insert and screws.

I had one instance where it was a little more tricky and had to push a little harder.

I could see that there could be a possibility where you might need to take out the wire insert and start 1 centimeter over.

There are a few things which I wish to point out on logistics and technique. There is a critical thing to remember for the helper who is pulling on the loose plastic.

He/she must be pulling at least 30 cm ahead of where the wire is going into the channel to allow the necessary slack to get the wire into the channel.

The same applies for the person inside the structure who is pulling on the end wall cover.

Inserting the wire insert is very much a wrist action and proper technique is probably even more important when doing 3 layers of 7.2 mil

Your thumb should be on the next equal bump (either up or down) so that you can apply some twisting action to the insert.

Never simply slide the insert up and down as this can abraid the cover.

I hope this helps

Norm