Greenhouse Canada

Features Crop Culture Inputs

January 30, 2008  By Melhem Sawaya

Time for pre-season tune-up.  A little preventive maintenance now will mean far fewer headaches in the spring

26With preparation for every seasonal crop, a series of steps are required before the actual production time. These steps are commonly called the “tune-up.”

We send our cars for a checkup before a long trip or during intervals of every so many kilometres. Athletes inspect their equipment before competition or a practice, whether it’s their rackets, bows or skates, etc.
I worked on a farm for a couple of years. Mr. Freeman, my boss, would always stress the need to get the machinery well-tuned ahead of the season for two reasons:


• It takes much longer to fix machinery after it breaks than a preventive tune-up requires, not to mention how inconvenient and frustrating it is to deal with equipment that has broken down when you need it most.

• Time and schedules must be met or the crop will suffer. Even in field production, you have a narrow window of opportunity for planting or harvesting. At the farm I worked at, there was a very short period available for planting. One day it might be too wet, the next day would be perfect, and third day it might be too dry. (You guessed it – we worked on clay fields!)

But the timing window for plug production is just as narrow, and preparations should be completed well in advance of actual production. Some of the things to check include the seeder, the germination chamber, the mist lines, the flat fillers, and the seed storage area (hopefully you have one by now and are not storing seeds in your desk!). You should also conduct a practice run with some seed to check the entire process. And most importantly, check to ensure your staff is ready and well trained.

The most important aspect of greenhouse profitability is having no shrinkage! This is not just about heating costs, or labour efficiency, or low prices, though these would all be factors of profitability. But compared to shrinkage, they are minor costs.

So here are some points that could help you with your plug production tune-up, and during actual production.

n Seed storage is very important. Do not open a container until you are ready to sow, and hopefully you will use it all. If you don’t need a large order, use several smaller packages.
Using leftover seed from the previous year is often a waste of time. Sow a small sample of it to give you a good idea of whether it is viable or not. Some seed stores better than others.

n For optimum seed germination and growth, a proper pH of 5.7 to 6.2 is a must. Soluble salts should be in the 0.4 to 0.8 range, a 2:1 dilution. Sodium and chloride levels should each be less than 40 ppm. Phosphorous levels should be in the 8-10 ppm range, or else the plugs will be completely stunted.
Good holding capacity is essential. Testing the media in-house and at a lab before seeding to see if the pH, soluble salts and other nutrients are within their acceptable ranges is the most important factor of plug production. About 90 per cent of plug problems are related to pH and soluble salt issues.

n The physical properties of plug flats are also important. The deeper the cell, the better it is for drainage because of the deeper columns.

Filling flats with the same density throughout the cell is also important to ensure even and consistent moisture levels during the plug-growing period.

The soil should be damp to the touch but not dripping wet. A quick way to check moisture content of the plug media is to grab a handful of it after wetting and squeeze it. If it drips, it is too wet. If it crumbles, it is too dry. But if it stays in one clump, then it is the right media wetness.

n Adjust your seeder so that there are no misses. Maybe it is time to change nozzles, check the drum or have a simple tune-up.

Pay attention to seed placement. Seeds placed near the edge of the cavity could desiccate, especially when we are trying to run the crop on the drier side.

If you are covering seed, never use fine vermiculite because the idea is to create a micro-environment of high humidity, not to bury the seed. Use of medium vermiculite of proportionally sized particles is recommended. Do not use the dusty leftover vermiculite.

If plug flats are passed through a watering tunnel, make sure the flats are evenly watered with gentle irrigation so the seed is not buried. This is especially important with very small seed.

Sown plug flats should not sit in the growing area too long because the minute the germination process starts, it should not be interrupted by a drying period. It is very important to sow the plug flats and have them moved into the germination chamber or propagation area to receive the humidity or water cycles as required.
Sown plug flats should be transported to the propagation area without being severely shaken, as this might bury the seeds more than is desirable.

n Plugs need to be fertilized at early stages, but at a low EC level of .75 mmhos  of total water and fertilizer. This is a recommended starting point, assuming we are starting with a low EC plug media.

Avoid the use of high ammonium fertilizers, especially early in the season when light levels are low. As well, the use of ammonium fertilizers is not recommended if you are trying to cool the plugs.

Many plug nutrition articles recommend to not fertilize with high phosphorous levels. The emphasis with this recommendation should be on the high rather than the not. Maintaining low levels of phosphorous in plug media is as important as any other element. A phosphorous level of 8-10 ppm in the plug media is important in the energy compounds, such as ATP, that the plant needs for synthesis and degradation. At the same time, high levels of phosphorous will cause plug stretch and inhibit the absorption of copper, iron, zinc and boron.

In simple words, moderation is the key. Test your media frequently to know your levels.

n Adjust the environment and treatments to support every plug stage. Do not treat all stages and seeds the same because they are not the same. The KISS (Keep It Simple, Silly) theory has limits before negative consequences occur.

n Many methods can be used to regulate growth, but with our low light levels early in the season, we depend more on chemical growth regulators. Pick the right growth regulator and the right rate to use on your plugs.

The rate and type of growth regulator to use varies with:
Temperature – higher temperatures require higher rates.
Light levels – the higher the light
levels, the less growth regulators are needed, especially if that crop flowers with accumulated light levels. Geraniums are a good example.
The type of grower you are – wet or dry.
Greenhouse environment – glass vs. poly.
Humidity – greenhouses with high humidity require higher rates of growth regulators.
Cultivars – those within the same genus require different rates, for example, red petunia vs. purple.
Varietal selection – this will determine the rate of growth regulator to use, for example fantasy petunia vs. wave petunia.
Light vs. heavy spraying – the rate changes with a grower’s habit of applying growth regulators. This is why we should spray with a pre-determined volume per area.
Plant conditions – if the leaves are wet when we are spraying, then the rate is much less effective, if it is effective at all.
With all these variables in mind, the only way to know what rates to use is by doing your own trials based on recommended rates and judging for yourself.
Please note: many of the label recommendations are based on a very hot and sunny environment, so the rates will be too high for Canada and northern states.

The previous steps are more applicable if you propagate your own plugs. Here are some guidelines if you purchase your plugs:

1  Make sure you calculated your growing correctly and don’t try to grow that extra 5-10 per cent, because this will put the rest of the production into a squeeze. It will
definitely cause a reduction in efficiency and quality.
2  Plan for your plugs to arrive on the week you are planting and not a week earlier, because that extra week will spin into diminished quality and increase the risk of losing them simply from overwatering or, more likely, forgetting to water them for a day.
3  Plant the same week you receive your plugs. Don’t postpone the planting due to shipping or any other reason. What is not done correctly during planting will show its negative impact at shipping.
4 Calculate your labour capacity on how much you can plant in any specific week and order only the amount of plugs that you are able to do in that period. Ordering to a plan different than the growing schedule is only a good idea if you plant on time and space on time.
5  Make sure you do not program your plugs to finish at one date, even knowing you will not sell them all in that week.
6 Warmth-loving crops are badly set back if planted when outdoor temperatures are still below 16ºC-17ºC.
7  Order plugs to extend the season, but only in moderation and only if you have a home for them.
8 Only grow what is ordered. You know from past years what you can sell.
9 Grow varieties that will perform well in the garden. If we do not care about garden performance, we better invest in sod farms or, more likely, concrete or asphalt contracting companies, because your consumers won’t return if you grow varieties that don’t perform satisfactorily, year
after year.

Melhem Sawaya of Focus Greenhouse Management is a consultant and research coordinator to the horticultural industry. Comments on this or any other article
are always welcome by e-mailing him at

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