Last week I received a request from fellow blogger and tweeter Eden Balfour to explain how we decide whether to start particular crops indoors or to direct seed them into the field. Here's a quick overview.
The first factor determining whether we start transplants indoors concerns how early we can get a crop and what the overall outcome for a crop will be. For example, we start alliums (onions, shallots, leeks) indoors in February. This family needs a long season and is photosensitive, meaning its plants respond to daylight hours to bulb up. It needs to be well established before solstice in order to take full advantage of the season's daylight.
We can get earlier crops of almost everything we grow by doing early plantings indoors. We do this for brassicas (cabbages and broccoli), lettuce, fennel, squash, tomatoes and cucumbers. Many of these crops are seeded every week in order to have a continuous crop or to ensure we have a plant ready to go in the ground when the weather is right. Squash, for example, does not hold well in transplant pots. We seed our crop three times over three consecutive weeks to ensure we have at least one set of healthy plants when the weather is right for transplanting.
In another example, we previously only direct seeded corn. But due to the low spring temperatures, we often didn't get proper germination or an early crop. By doing transplants this year, we found that we could get an early crop of sweet corn with no gaps in the bed space from poor germination. This helped to make the most out of every inch in the bed.
The second factor we consider is the cost of the seed. In the past, we did early fennel plantings indoors and later plantings were seeded directly into the beds. But the cost for 10,000 fennel seeds is now over $300. We weren't getting the germination we desired doing direct seeding and the weeds out performed the fennel in many instances. By doing all of our fennel as transplants we make the most out of our seeds, thus reducing some costs, while getting a better crop in the end.
The third factor concerns weeds. For the vast majority of crops, if you can transplant them, you have a better chance of staying on top of the weeds. We don't use plastic mulch on crops other than cucurbits (squash, cucumbers), so being on top of weeds is crucial. By transplanting, we are able to give the crops a head-start.
Crops such as spinach, dill, cilantro, rutabagas, radishes, turnips, beets, parsnips and carrots are all best done as direct seeding. They generally germinate well and for most, because of their taproots need to have an undisturbed growing environment. For spinach, dill and cilantro, the volume being seeded every week means that direct seeding is most efficient.
When direct seeding, bed preparation is of particular importance. Being able to prepare a bed in advance (up to two weeks before seeding) gives weeds an opportunity to germinate. Prior to seeding, the bed can be weeded (hoed or with a tractor-mounted basket weeder). Alternatively, a few days after seeding, the bed can be flame weeded (i.e. scorching the weeds with a propane torch). This allows the crop to emerge into a relatively weed-free bed, thus having a head-start over future weeds.
The main advantage transplanting provides is control over the crop and generally earlier crops, plus some cost savings in seed. The main disadvantage is scalability (i.e. finding efficient ways of doing transplants for larger crops/operations) and cost of start areas, whether a growing room with artificial lights or greenhouse space.
We have done all of our transplants in plastics trays in the past. This year I tried experimenting with soil blocks, which help to hold plants for longer and reduce transplant shock. What I found, however, is that we will need an entirely different setup to make soil blocks work. We'll try more in the future, but they won't necessarily work for everything and will take more space, time and care to do successfully.
So, if anyone has any other transplanting tips, I would love to hear them. Please share!