To have a green thumb: to be gifted at caring for plants.
— Common saying
MOST VEGETABLES on our farm begin life as seedlings in a nursery that we set up each year to grow transplants. Given the choice between transplanting a crop and direct seeding it, we always prefer to transplant. The advantages of this method are worth all the effort and expense, especially if intensifying production on a small plot is the goal. The success of our growing operation therefore depends on our ability to start seeds indoors. Failed germination, slow growth, diseases, or any problems at the seeding stage can have disastrous consequences on the production calendar we rely upon for timely harvests. More than at any moment in the season, indoor seeding requires competence and attention to detail.
Having said this, producing transplants is only a small part of what we do in a season, and it is hard to justify investing in the most cutting-edge facilities and equipment just for this. The science of greenhouse horticultural production is very advanced, and mastering the best techniques would be a huge undertaking. In spite of this, we have managed to learn enough about indoor growing to suit our purposes and have developed systems for producing very high-quality transplants in a low-tech setup. For successful market gardening, this balance is important—one needs to develop the skill to produce large quantities of vigorous and healthy transplants without having to become a specialist. Here are the principles we follow at Les Jardins de la Grelinette.
There are many techniques for starting seeds indoors. Most amateur gardeners use open polystyrene flats or individual pots made of coconut fiber. On the commercial side of things, Eliot Coleman has been a long-standing proponent of soil blocking, a technique in which seeds are germinated in blocks of soil created by a press. Having tried this as well as other techniques, we settled for the more common way of growing transplants in cells (also known as plugs), which is an effective and proven technique that I strongly recommend.
Transplanting is the practice of starting seedlings in one place and setting them out later on in the garden.
Cell flats are plastic containers separated into many compartments in which the roots of the seedlings begin to grow. Flats are placed in containers called trays that add support for moving them around. Most flats are 11 inches wide and 21 inches long, an industry standard that allows for uniformity in tables and other nursery equipment, such as harvest carts for transporting transplants.
Advantages of Transplanting
Seeding begins before the start of the frost-free period, thereby extending the growing season considerably.
Germination and growing conditions are controlled in the early stages, when plants are the most vulnerable.
The chances of crop success are improved because seeding density is perfect and crops have a head start over weeds.
It is possible to do succession plantings by starting crops in the greenhouse even before garden space is available.
Planting cells come in a variety of sizes. It is important to select the size of plant cell for the particular type of plant you are growing. A chart of recommended plant cell sizes can be found at the end of this chapter.
Flats have anywhere from 24 to 200 cells, which determines how big the cell size is. You then choose the correct cell size in accordance with the soil volume required by the roots and with the number of days each crop will spend in the cell. Each plant’s root system will develop within its own cell, making it easy to transplant them individually to specific sites or containers (their roots do not become tangled). In our nursery we use flats of 72 and 128 cells, and bigger individual pots of four inches in diameter for seedlings that are potted up.
There are many advantages to working with cell flats: they are easy to handle and fill, drain well after watering, and create clumps of soil that hold together well — which is one of the keys to successful transplanting. They are also durable and reusable, although not entirely indestructible. A few always make their way into the garbage by the end of each season, which is certainly one of their drawbacks. Since flats are used from season to season, you must make sure that they do not become vectors of different plant diseases. In our years of using flats, we have never washed or sterilized them, and have never had any problems. We do, however, always empty ours completely and spread them out to dry in the sun for a few hours at the end of each transplanting session.
Working with the proper soil mix is a very important aspect of growing seedlings in cell flats. Since all basic plant needs (air, water, minerals, etc.) must be met with only a small amount of growing medium, the ingredients of the mix must have specific characteristics (drainage, water retention, aeration, fertilization, salinity, pH, etc.). A soil mix is therefore not something that can be improvised, and for this reason, buying a commercial mix is perhaps a better option than making it yourself. When doing so, it is important to choose a top-quality product and make sure it is not treated with synthetic wetting agents. Most certified organic mixes are suitable.
This being said, preparing one’s own mix is neither difficult nor complicated. Here is an “all-purpose” recipe that we have used successfully for many seasons. (Our buckets have a volume of 4.2 gallons.)
• 3 buckets peat moss
• 2 buckets perlite
• 2 buckets compost
• 1 bucket garden soil
• 1 cup blood meal*
• ½ cup agricultural limestone
These ingredients are found in most mixes, and you can research their origins and characteristics if you wish. There are certain details to note, however:
• Peat moss is the main component of the mix and should be top-quality. Avoid peat moss that is too coarse or too fine.
• Perlite serves as an aggregate and plays a key role in drainage and aeration. In this recipe, it can be replaced with vermiculite, especially when used in larger cells (flats of 72 cells or fewer).
• Compost must not be leached of its nutrients and must be fully mature (i.e., completely decomposed and not warm to the touch) in order to avoid germination problems. We use the same compost for this as we use in our gardens.
In the United States and Europe, coconut fiber is often presented as a green alternative to peat moss, but I have my doubts that importing precious organic matter from the tropics is more environmentally friendly than using a local resource.
• Garden soil is used to “cut” the compost and to lower the salinity. Use a light soil (not too sandy, not too heavy with clay). I prefer to use soil from our garden rather than sterilized garden soil so that living material is introduced to the mix.
• Blood meal supplies the extra nitrogen required by heavy feeders. Feather meal can be substituted for blood meal in this recipe.
• Agricultural limestone is used to raise the pH of the mix, which has a tendency to be low owing to the natural acidity of peat moss.
The mixing can be done directly in a wheelbarrow. For best results, we mix the limestone into the peat moss first. The rest of the ingredients are then incorporated one by one with a shovel. Working with dry ingredients makes for a more homogeneous mix, but it’s also important that in the end the mix be well moistened throughout. We find it best to water it as we go along in the process of mixing all the ingredients.
If you decide to make your own mix, be sure that the recipe you use is appropriate, given that root development will be limited by cell volume. In other words, ensure that the mix is designed specifically for growing in cell flats rather than other types of seeding containers.
The mix must be sifted to remove rocks and other large debris to ensure a consistent product. When watering the flats, uniformity in the cells will make an important difference. We sift our mix using a wooden frame with a metal mesh stretched across it. The holes of the mesh are about half an inch square. All and all, making your own mix is a simple process, but it can be tiring. There are, however, some ways to ease the workload. For example, some farmers use cement mixers to stir their soil mix.
Flats must be filled with the proper technique in order to conserve as much air retention capacity as possible in the soil mix. This makes a big difference with regard to proper root development of the seedling. Our process is as follows.
The first step is to make sure the mix is thoroughly wet. It should be sticky—just before the soil holds together in a ball. If it is not wet enough, we add more water to the mixture, which we stir again with a shovel until it is just right.
The cell flats are then filled to the brim with the sticky mix, and the excess is cleared away with a straight piece of wood or a brush. Once again, it is important that the cells be filled uniformly: those with less soil will dry out more quickly, which makes watering a more difficult job.
The mix is then packed lightly, by lifting the flats about two inches into the air and letting them drop onto a flat surface. Once the cells have been seeded, we cover the seeds with a fine layer of dry soil mix to prevent them from drying out too quickly. In the end, the flats should be five sixths full to ensure enough space for water retention.
For a number of years, we have organized a garden plant sale—to great commercial success. Since our production of transplants has increased so much, we have started using a purchased certified organic soil mix. Once production reaches a certain level, this option becomes very attractive.
The very last step is to arrange the seeded flats in the nursery. It is important that flats with the same number of cells be grouped together to ensure uniform watering.
Certain crops that we want to produce early (e.g., tomatoes, leeks, and onions) must be started as soon as spring arrives to be ready to harvest early in the season. Given how expensive it is to heat a greenhouse during the very cold month of February, it is a good idea to start the seedlings inside your house, in a place that is already heated, where flats can be spread out and watered, and where soil mix can be handled. We refer to this space as a seedling room, and there are many ways to create one. Here are the main factors to consider when planning one.
The main objective of a seedling room is to be able to control growing conditions perfectly. The ideal average temperature for plant growth is 18°C to 23°C (64 to 73°F) in the daytime and 18°C (64°F) at night. The temperature in our seedling room is regulated with baseboard heaters, but any heating system will do, provided that the heat is not blown directly onto the plants. The relative humidity in the room should be 60 to 90%, which is easily maintained with a timer-controlled vaporizer (e.g., this can be set to mist for 10 seconds every 20 minutes). The seedling room should be lined with polyethylene to trap in heat and humidity. A small fan is also helpful to prevent fungal disease resulting from a buildup of stagnant air.
To avoid compacting the cell flats when filling them, make sure they are stacked at alternating angles rather than inserted into each other.
Because the day length in February and March is too short for optimal plant growth, extra lighting is require so that the plants receive 14 to 16 hours of light per day. There are a number of solutions for this, but the simplest and cheapest is to position fluorescent tubes above the flats. In order to provide the plants with the full spectrum of light, you will need both cool white and warm white fluorescent bulbs; the latter produce infrared radiation and are generally designed for bathrooms. To prevent plants from withering, the lights should be adjustable in height and positioned about four inches above the tips of the plants as they grow.
To speed up the procedure when seeding flats, we use a homemade vacuum seeder, also known as a plate seeder. This simple yet brilliant device uses a vacuum to hold seeds onto a flat plate drilled with small holes to match the seed size and pattern of cells in a tray. You then flip over the plate onto a filled cell flat and shut the vacuum off, letting the seeds fall into place.
Most vegetables require a higher temperature to germinate than they do to grow. In order to ensure optimal growth, the seedling room can be equipped with heat mats that plug into a 110-volt outlet. With these mats, the soil temperature is kept at an optimal germination temperature, about 25°C (77°F) day and night. Contrary to popular belief, darkness does not help seeds germinate—but soil humidity does, which is why we water frequently and sometimes keep our flats under floating row cover.
A seedling room is ideal for starting a small amount of indoor production, but once a certain number of seedlings are started, it becomes inevitably necessary to move into a bigger space. A greenhouse dedicated to the production of transplants is therefore essential in any market gardening operation. This requires a major investment in infrastructure, for the building as well as for heating and ventilation equipment.
When we planned our nursery at Les Jardins de la Grelinette, the option we found that made most sense was to set it up in a greenhouse that would also be used for growing crops during the summer season, rather than investing in a smaller permanent greenhouse intended exclusively for producing transplants. Our reasoning was that since we needed a nursery only for about 12 weeks out of the year, having multiple uses for one building made more economic sense. We also liked the idea of using some of the heat provided for the nursery for other early direct-seeded crops as well. Our evolving plant nursery addresses both these objectives.
At the end of the winter, we set up the nursery in part of our large tomato greenhouse, which we section off with a piece of polyethylene film. The partition is clipped to the hoops of the greenhouse, making it easy to move. This allows us to increase the heated space gradually as our transplant production progresses. Since only part of the greenhouse is being used as a nursery, we seed the remainder of the space with early vegetables that we plan to harvest for our first market. All in all, the nursery takes half a day at most to set up. It is simply a matter of laying a geotextile ground cover (to prevent weeds from taking root) and installing movable tables.
As the spring wears on, the outside temperatures get warmer, and some of our inside seedlings are transplanted out into the tunnels and under floating row cover in the gardens. We take this opportunity to reorganize the nursery, reserving a section for the tomatoes that are ready to continue growing in the ground. The polyethylene partition is removed, which allows the greenhouse to warm the tomatoes, the transplants, and the early crops. Once the danger of frost is behind us, we move all of the transplants outside. In our climate, this usually happens around the end of May or the start of June. At that time, we also harvest the greenhouse crops (usually beets and carrots) for the first market, and the rest of the tomato plants are quickly planted over the entire greenhouse space.
All of this involves a lot of handling and planning, but it allows us to use the heated space optimally. Considering how expensive fuel can be, this game of musical chairs is well worth the effort.
Heating and Ventilation of the Nursery
No matter how a nursery is organized, it needs proper heating and adequate ventilation to produce good transplants.
One classic mistake beginning growers often make is to set the greenhouse thermostat lower than the optimal temperature for plant growth (18°C/64°F at night) in an effort to save money. This is understandable considering how often the furnace will run on through the night—but in the end, this amounts to cutting corners. Plants kept at a lower temperature will grow more slowly, which delays production. Given how short our growing season is, we have to make transplants grow as quickly as possible. When it comes to saving on heating costs, it is better to improve equipment (e.g., better greenhouse insulation, more efficient furnace, thermal screens, etc.) rather than adjust the temperature. Especially important is making sure that the greenhouse is shut up tightly at the end of the day to keep out the cold wind at night.
In our house, we use a hallway with south-facing windows as our seedling room. This space is next to the family kitchen, so it is easy to keep an eye on everything.
The wooden seedling tables we use are placed on concrete blocks. These are easy to build and move. To make the best use of the available space in our greenhouse, we have some tables that measure 4' × 8' and others that measure 2' × 8'.
The large tomato greenhouse is divided in two by a piece of polyethylene clipped to the hoops.
Purchasing a furnace for your greenhouse is one place where you don’t want to be cheap. Get a new one (or refurbished) and make sure it has enough BTU to rapidly heat up the space.
Regarding which heating system is better—oil, propane, or gas—they are roughly the same in terms of heating and equipment cost. In my opinion, none of them is environmentally friendlier than the other. Heating with a wood furnace is also an option, but one that I do not recommend. Waking up a couple of times per night to fill the stove is a hardship, and wood furnaces aren’t as easy to keep at a set temperature. With heating systems, the most important thing is to acquire a furnace that is in excellent condition, powerful, and above all, reliable. It’s also important to make sure that the furnace is the appropriate size. A small furnace that takes forever to heat the space will actually burn more fuel than a large one that brings the greenhouse to the correct temperature quickly. It’s also worthwhile to investigate the reliability and speed of the services offered by different fuel suppliers. Some have special rates for farmers, so it is always a good idea to ask. Also, to avoid a fuel shortage, always ensure that your tank has plenty of fuel on nights when you expect frost or very cold weather.
To ensure uniform heat distribution, perforated polyethylene pipes may be used; these are attached to the furnace and installed under tables in order to heat the seedling flats first. The perforations must be calibrated according to the size of the pipes and their spacing inside the greenhouse. Most greenhouse equipment suppliers offer this service.
To cool the nursery on sunny days, different options are possible. We decided to go with natural ventilation in the form of roll-up side walls. While there are a number of forced air fans available that can ventilate more precisely, we appreciate the passive quality of this system that simply uses wind to clear the air. To keep the cold air from touching the transplants too directly, we installed “skirts” along the greenhouse and place our seedling tables below the level of the side openings. This is a very common feature that greenhouse manufacturers can help you set up.
When it comes to regulating humidity, we have gotten in the habit of rolling up the sides for a few minutes very early in the morning to allow any humidity produced through condensation during the night to escape. I also recommend doing so while the furnace is heating the air. This procedure prevents excessive humidity from stagnating in the nursery and works wonders. In all of our years growing, we have had no major fungal disease in our nursery to date.
Finally, one of the most essential tools in any nursery is a thermometer with an alarm that allows you to set maximum and minimum temperatures. In the event of a furnace breakdown, power failure or fuel shortage, our alarm alerts us that our seedlings are in danger. This is particularly important on frosty nights, when a few hours without heating can be fatal to plants. We’ve had such circumstances happen more than once, and fortunately, we had a backup plan. If the furnace breaks down, we have an auxiliary furnace in the greenhouse that we maintain regularly. This second furnace is much less powerful (and less expensive!) than the main one, but it keeps the greenhouse just warm enough until the main one can be repaired. After several seasons of denial, we also reluctantly bought an emergency generator for use if the power were to go out for several days. This was a large expense and will probably never be used, but we would stand to lose if we didn’t have it available as a backup. As my grandfather used to say, “Sometimes you need to wear suspenders with your belt.”
The alarm on our thermometer also warns us if the greenhouse is at risk of overheating during the daytime. Forgetting to roll up the sides when the sun comes out can result in a greenhouse full of dead seedlings in less than two hours! Such a catastrophe would be disastrous for the whole length of the growing season, and therefore this is not a wise place for gambling. An alarm thermometer is absolutely indispensable in the nursery.
Water management is essential for producing successful seedlings. Like an overheated greenhouse, a water shortage can quickly kill plants—but, on the other hand, too much moisture in the soil mix can lead to fungal diseases. The question of when and how much to water is a complicated one, involving the consideration of many factors:
• Watering must be done in a uniform fashion. Every tray of the same cell size should get the same amount of water, so that none of them dry up faster than others. Obviously, pots and trays with bigger cells will require more water. It’s therefore important to organize the layout of the flats accordingly on the tables, i.e., flats of 72 cells together on one set of tables and those of 128 cells on another.
It is a good idea to cover seedlings with a thick floating row cover or even a polyethylene film at night. There are different designs that make it easier to cover and uncover the plants. Thermal screening is an inexpensive way to reduce heating costs.
• It’s important to water in accordance with the location of the trays in the greenhouse. Flats generally dry out faster at the table edges, on the south side of the greenhouse, and closer to the furnace.
• Watering is a task that must always be done twice: once to moisten the soil via capillary action and once to water deep down.
• When watering, it’s important to consider the outside temperature: sunny weather calls for heavy watering, while cloudy weather calls for light watering—or none at all. Devastating diseases such as “damping off” arise in soil mix that stays soggy for too long. Also, plant leaves that remain wet for too long can act as an entry point for various fungal diseases.
Managing all these factors requires special sensitivity that one gradually develops through careful and continuous observation of the growing medium and the appearance of the seedlings. For this reason, it’s a good practice to have only one person do watering inside of the nursery. Having the same person in charge also ensures that this essential task is never forgotten. This person may delegate on occasion, but never for too long. This is a policy I highly recommend.
It is also important to make sure the water used is not too cold, as this will slow the growth of the seedlings. Our solution is to have a large water tank (265 gallons will do), which we fill up every other day. The heat of the greenhouse warms up the water, which would otherwise come directly from our well. To heighten this effect, we painted the reservoir black. This is also a good way of preventing algae formation in the tank. The reservoir is linked by pipe to a pool pump that is equipped with a pressure tank. This allows us to water as much as we need without always having to switch the pump on and off.
Potting up is a technique that consists of transferring seedlings from small cells into bigger ones. This practice gives plants that spend a long time in cells (tomatoes, peppers, cucumbers, and eggplants in our case) the benefit of extra root space and rich new soil mix to further their development.
The procedure is simple yet delicate. The seedlings are fragile and can experience stress if their roots are damaged. When potting up, we make sure to hold each plant by its stem and extract it from its cell by pinching the cell bottom and gently tugging the plant. If plants are potted up at the correct stage, the roots will generally occupy enough space in the cell so that the clump holds together well. To ensure that we grow only the most vigorous transplants, we never pot up weak or sick seedlings—these go into the compost along with their used soil mix.
Watering seedlings is a fine art: finding the balance between watering too much and not enough requires attention to detail.
You must be especially careful when potting up Cucurbitaceae, which do not like it when their stems are buried.
Transplanting into the Gardens
Transplanting is an exciting time. After months of nurturing the seedlings, they are now ready to fill up the garden, which then quickly takes form. However, most of the transplanting also happens during spring rush, when everything needs to be done all at once. Therefore, we try to organize this operation as efficiently as possible.
The first thing we do is prepare the plants for the shock they will have when moved outside. Since they have spent their whole lives up to this point in an ideal, regulated growing environment, they are not yet used to wind, rain, and outside temperature variations. One week before the transplanting date, we put the seedlings on tables just outside the greenhouse and cover them at night with floating row cover. If frost or very cold temperatures are expected, we bring them back inside the greenhouse. The purpose for this is to get the plants accustomed to the elements gradually.
During the hardening off period, we prepare the beds and make sure they are ready to receive the transplants: soil is amended, beds are broad-forked, and plastic mulch and drip irrigation are installed where necessary. We watch the weather forecast very closely at this time in order to seize the most opportune moment for transplanting. We transplant in the morning in cloudy weather and in the late afternoon in sunny weather—but if it is too hot or if the seedlings are transpiring excessively, we postpone the operation altogether.
Once the beds are fully prepared, we make sure to give all transplants bound for the garden a thorough watering. This step is very important, as plants take best when there is already a good amount of moisture in the potting mix: the soil in the garden is relatively dry and tends to draw moisture from the transplanted clumps. Therefore, each flat is watered multiple times in order to saturate the clumps with water. They are now ready to be brought out to the gardens in a harvest cart.
Because of our crop plan (see Chapter 13), all of our transplants are to be set out in a specific location in the garden. To make sure there is no mistake about where everything goes, we make notes resembling the ones shown in the table on page 94. This practice also helps us make sure we are not carrying more trays than needed, or that we bring enough. Like I said, we try to be as efficient as possible because we don’t have time to spare. The devil is in the details.
The way we set out our transplants is fairly simple. Working in pairs (or as a trio, depending on the crop type), we work side by side extracting the plants from the cell flats before planting in the ground. To make sure the transplants are spaced correctly, we plant the seedlings in rows that have been previously traced in the soil with a rake (the same raking technique is used to mark the rows for direct-seeded crops). The fastest person of the two (usually me!) will also space the plant on the row using a ruler as a measure.
When putting transplants into the ground, there are two things we watch out for. First, it’s important to avoid leaving air pockets between the clump and the hole. The transplants need to be firmly rooted by pressing them lightly into the soil. It’s also essential that the clump be buried completely, as it will dry more quickly if left poking out of the soil. By the end of the process, the surface of each clump should be level with the soil surface. These are the instructions we give to everyone who helps us transplant.
For the next few days after transplanting, we make sure the ground stays moist. The plant roots cannot go without water at this stage, or else the crop will be fragile throughout its growth. If the weather forecast calls for sunny or partly sunny conditions, we install an irrigation line to keep the plot watered. Given that crops kept under row cover are particularly susceptible to wilting in excess heat, we take no chances: if it is sunny for the first few days after transplanting, we uncover these crops. This also involves a lot of work, but at this final stage of transplanting, every precaution protects our investment.
At the current time, we are experimenting with a new marking roller that allows us to mark lengthways and crossways at the same time. Clever in its design, this roller can quickly adjust to different spacing. See the tool appendix.
* The number of flats per bed is calculated based on a 100-foot bed length and includes a seeding density 30% higher than necessary. This safety factor is important as it allows us to compensate for losses at the time of planting, or for poor germination in the nursery.
** Crops in the Liliaceae family are broadcast in open trays (without any cells).
* When potting up with this recipe, we double the amount of blood meal.
