Season Extension

What is season extension?  In short, it is providing shelter to plants against the worst of the weather, either before and/or after the main growing season.  The growing season itself is traditionally defined as first and last frost dates in any given area, since that often dictates which plants can or cannot go outside without some form of protection.  However, it's actually quite a bit more complicated than that.  The growing season often dictates what we can grow, our work load during any given timeframe, when we can offer products at market, when we need to harvest, and sometimes even the income we can earn any given year.  So season extension is a way to give ourselves more options.  if we can get started with our growing activities earlier in the year, we can take some of the rush out of the start of the season.  If we can extend the growing season a bit, we can harvest later into the year, and sometimes grow/harvest long-season crops that we wouldn't have time to produce otherwise.  Depending on our location, season extension might be just a week on either side of the first/last frost dates.  In other locations, careful season extension might actually give us several additional months of additional growing time.  

So what kinds of options do we have for season extension?  Greenhouses immediately come to mind as one very common form of season extension.  Ask almost anyone what a greenhouse is, and what it's used for, and they'll be able to tell you even if they've never actually worked in one.  Yet greenhouses are only one form of season extension.  We have hoop houses, germination cabinets, cold frames, hot frames, heating cables, heating tables and various other forms of microclimate modification available to us and our plants.  If we want to take a comprehensive look at how any of these methods fit into "the big picture" of hydroponic growing, we see that they are another set of tools in the toolbox for creating optimal growing conditions.  In that regard, they are not very different from our HID lighting, nutrient solutions, growing media and other elements of soilless agriculture.  So in that sense, greenhouses in particular and season extension in general fit hand in glove with other growing optimization methods.  We address all those other optimization elements elsewhere in the website.  Here, we'll talk about various forms of season extension as a group, and look at their various pro's and con's.

To be sure, season extenders in general offer some very appealing advantages.  The extension of favorable growing conditions can give us extra production for whatever fruits and vegetables we're trying to grow.  Sometimes those extenders give us the chance to grow things which otherwise would never survive in our particular climate.  Perhaps we're trying to grow those crops for our own use, or perhaps we're growing them for sale to others.  In either case, season extenders give us a lot of flexibility in what we grow, when, and how.

On the other hand, any form of climate control has pro's and con's.  Greenhouses can become an oasis for destructive insects, rodents and diseases.  Smaller season extenders such as cold frames and hot frames can suffer from fungal problems due to high humidity and poor air circulation.  Those same small frame can actually heat up too much on unexpectedly sunny days, or provide insufficient protection during colder than expected conditions.  And the physical structures can also present their own complications. Wind loads, snow loads, precipitation drainage, and anchoring all become issues, particularly with the bigger commercial structures. Strut size, covering material, ventilation, humidity control, CO2 supplementation and even electrical or water hookups will bring new complications into the field or garden, which wouldn't be there with simpler setups.  So there are serious considerations before investing in any form of season extender.

Season Extension Pro's and Con's

As with any set of tools, season extension has a list of pro's and con's.  No one method is perfect for every situation.  Thankfully, we have a lot of options, and in some cases either hundreds or even thousands of years worth of collective experience.  We'll be drawing here from soil-based agricultural practices in some cases, which might seem to be taking us off-topic.  However, the vast majority of advantages which season extenders bring to soil-based crops, they also bring to hydroponic crops.  If there are important differences or exceptions, I'll point them out along the way.

Can Season Extension Methods Be Combined?

In a word, absolutely.  That's one of their strengths.  Many season extension methods very naturally work well with each other, or complement other season extension options.  In fact many growers regularly combine different forms of season extension to optimize the cost versus the benefits.  For instance, an un-heated greenhouse may be most valuable as a work environment shielding growers and equipment from the worst of the weather.  Heating that entire space might not be cost effective for the plants themselves.  However, the greenhouse would provide extremely effective protection against wind and precipitation.  The plants themselves could then be heated (often at much lower cost) via root zone heat sources.  Tender seedlings could be sprouted in a germination cabinet within the greenhouse, such that the most vulnerable plants have the greatest amount of protection.  For growing areas without a shell, hardier plants which can tolerate a wider range of temperatures, and may only need floating row covers over them on colder nights to provide a few extra degrees of protection.  So this list of techniques can definitely be considered a mix-and-match collection. 

Also keep in mind that many of these methods offer benefits which go beyond season extension.  For instance, floating row covers will provide a few degrees of frost protection, while also protecting plants from flying insects and birds.  Hoop houses which provide a growing space during the season, can also be used for equipment storage during the off-season.  Many growers pride themselves on finding as many different ways to use any given piece of equipment, in as many different ways as possible.  We'll try to list as many different applications for each method as we know about.  However, the gift of creative thinking will undoubtedly come up with more.

Season Extension Methods

The following table is a summary of season extender methods, ranging from lightweight and/or temporary methods, up to more costly, complex and/or permanent methods. Please see the hyperlinks to read more about each type of protection. We originally put this comparison table together on our parent website, frogchorusfarm.com.  There, we used it to describe how various season extender methods could help with soil-based growing.  Here, we'll modify it to specifically address hydroponic growing.  Whether you're a hobbyist, growing for a farmer's market or CSA, or selling your produce wholesale, it may be cost effective for you to explore one or more of these season extension options.

Season Extension Type	Temp Change (deg. F)	Common Uses	Cost	Complexity	Durability
Floating Row Cover	5	Severe weather protection for cool-hardy crops.	Low	Low	1-3 Years
Cold Frames	10-20	Germination boost and severe weather protection for cool-hardy crops.	Low	Low to Moderate	1-5 Years
Hot Frames	20	Germation boost and severe weather protection for tender seedlings.	Low to moderate	Low to moderate	1-5 years depending on heat source
Soil Heating Cables	5-20	Germination boost and accelerated growing for high value seedlings.	Moderate	Moderate	3-10 years
Low Tunnels	10-20	Early/Late season protection for all crops; allows for all-season harvest.	Low to Moderate	Low	3-5 years
High Tunnels	10-40	Early/late season protection for all crops, with walk-in access and fewer thermal swings; allows for all-season harvest.	Low to moderate	Low to moderate	3-5 years
Germination cabinets	30-50	Germination boost and humidity control for tender seedlings.	Moderate	Moderate to High	5-10 years
Reemay in hoophouses	5	Provides extra buffer against extreme cold snaps.	Low	Low	Indefinite
Unheated greenhouse	10-40	Early/late season protection for all crops, with easier access and fewer thermal swings; allows for all-season harvest.	Moderate to High	Moderate	5-10 Years
Heated Benches	20-40	Germination boost and accelerated growing for high value seedlings.	Moderate to High	Moderate	5-10 years
seedling tray covers	10-30	Germination boost and humidity control for tender seedlings.	Low to moderate	Low to moderate	5-10 years
Heating Mats	20-40	Germination boost and accelerated growing for high value seedlings.	Low to Moderate	Low to moderate	5-10 years
Heated Greenhouse	20-50	Early/Late season protection for all crops, with easier access and fewer thermal swings; allows for all-season harvest.	High	Moderate to High	10-20 years with replacement film
Heated, passively ventilated greenhouse	20-50, ceilings on high temps	Early/late season protection for all crops, with easier access and fewer thermal swings; allows for all-season harvest. Controls buildup of heat and humidity, reduces heat stress and humidity-linked diseases/pests.	High	Moderate to High	10-20 years with maintenance
Heated, actively ventilated greenhouse	20-50, ceilings on high temps	Early/late season protection for all crops, with easier access and fewer thermal swings; allows for all-season harvest. Controls buildup of heat and humidity, reduces heat stress and humidity-linked diseases/pests.	Very High	High	10-20 years with maintenance
Heated, actively ventilated, artificially lighted greenhouse	20-50, ceilings on high temps	Early/late season protection for all crops, with easier access and fewer thermal swings; allows for all-season harvest. Controls buildup of humidity and humidity-linked disease/pests. Supplemental heat and light allows for year-round growing and harvesting.	High	Moderate to High	10-20 years with maintenance

A Work In Progress

As in other areas of this website, this section is a work in progress.  If you'd like to see some method addressed here that we haven't listed yet, or if you know of pro's and con's for any given method which we haven't yet listed, by all means Contact Us and we'll address it.  As we like to say around here, "mo' info, mo' betta!"