Seedling Success – Timing is Everything

It’s that itch, I tell ya, it gets me every time. As soon as the days start getting longer, and the seed catalogues start showing up in the mailbox, I just have to plant something. So, I pull out the storage boxes where I keep my surplus seeds and I look for something that takes 22 weeks to mature. This year it was pansies. Flowers are a good way to scratch the itch.

But when it comes to the vegetables and fruits that we want to grow in our gardens we need to rein in our wild horses and devise a plan. Not everything needs to be started early, and some things need to be started earlier than others. Still others have special fancy requirements to keep in mind (I’m looking at you, artichokes).

After you’ve chosen what you’re going to grow, and you’ve figures out how much of it you’re going to grow, it’s time to decide what, if, and when.

Do or Do Not

Unlike what Master Yoda would have you believe, when it comes to gardening it’s basically all try. But he got the first part right; do or do not is a big question when it comes to starting seedlings. The advantage of starting seedlings is that your plants get a longer growing season than they would if you seeded them directly outdoors, this is important if your season isn’t long enough, or if your planting season doesn’t align well with the need/tolerances of your chosen crop. Tomatoes, for example, transplant well in Ontario in May, but our ground is still much too cold for their seeds to germinate and thrive at that same time. If you planted tomato seed it could be weeks before it even sprouted; if it didn’t rot first.

The flip side of that is nearly all seedlings experience transplant shock when they’re placed in the ground. Some experience it more than others. Tomatoes tolerate transplanting very well and can be transplanted at almost any stage or size and will go on to thrive in the garden. Cucumbers, melons, and squashes, on the other hand, resent their roots being messed with and so require a delicate hand when transplanting. Members of the brassica family (except cabbage) need to be transplanted on time and in the right conditions or they may experience “buttoning”, which results in reduced yields, misshapen growth, or sometimes just no top growth at all. Buttoning can come from spending too long in the seedling stage or from the shock of being planted to early or late in the growing season.

I’m going to start by undercutting my whole premise here by saying that, effectively, you can start anything you want early and transplant it into the garden. Several years ago, I saw corn seedlings for sale at the local nursery and while that sight still perplexes me to this day, it is a doable thing. Also, do not start corn seedlings.

Additionally, most of our root crops – carrots, beets, radishes, parsnips, etc – are not started from seed. They can be, I’ve seen people start and transplant beet seedlings before, but it’s usually not necessary and it adds a level of complication to your early gardening season that I think most people don’t need.

Lettuce seedlings are a doable thing, especially if you’re trying your hand at head lettuces, but again they’re mostly not necessary. The advantage you can gain here is a lettuce that’s a few weeks grown by the time your summer starts to heat up. Balance that with the potential for transplant shock and extra care required for your baby lettuce seedlings.

The obvious dos are nightshades (tomatoes, peppers, and eggplant) and their ilk, as well as everything in the brassica family (cauliflower, cabbage, broccoli, Brussels sprouts, and kale), alliums (onions from seed and leeks), and herbs (including celery, excepting cilantro). And the more do-than-don’ts: the cucurbits (cucumbers, melons, squashes, gourds, and pumpkins), although there’s an asterisk with this one as noted above and below.

The don’ts – as noted above your mileage may vary – are root vegetables, leafy things (lettuces, bok choi, spinach – they just grow so fast), kohlrabi, and sweet corn.

The weirdo-maybes are beans and peas because I see a lot of people doing this, and it’s very, very easy to start them indoors, but I’ve seen no reason to try this myself.

Now

There are some things that you can start very early and get away with it for a long, long time. Alliums – onions and leeks – will keep in the seedling stage for weeks and weeks and wait patiently until you place them in the ground. They are also long growing crops, so they need to be started very early in the growing season if you want them to succeed in the first place.

Next comes herbs. As plants that thrive in a multitude of conditions – including being grown exclusively in pots – herbs can be started very early and can be kept in the seedling stage, or be allowed to progress to adulthood before being planted in the garden. Herbs rarely suffer much from transplant shock (parsley is a slight exception).

Eggplants, then peppers, then tomatoes in that order, about a week or so apart. Eggplants take the longest to germinate and develop and have that highest tolerance for remaining in the seedling stage before being planted out. Then peppers, who also take a long time to grow. And finally, our staple the tomato, the last of the early-earlies and also the fastest to grow. Tomato seedlings should be started about 8 weeks before their plant-out date – somewhere around the third week of March in Southern Ontario – but can be started earlier than that if you’re worried about growing time or prefer larger transplants. Unlike their cousins, however, tomato seedlings don’t hit pause in their seedling tray cells when they reach a certain size. They keep growing, and growing, and growing. They are vines after all. The good thing about this is that if you end up with wild, ranging tomatoes, you can just plant them more deeply in the ground – or even sideways – as tomatoes will sprout roots all the way along their stems.

Ain’t nature grand?

Then

As mentioned before there are some seedlings that don’t like to be messed with, or that are temporally temperamental. These are the cucurbits and the brassicas. With these you need to aware that you’re making a commitment to doing things on their terms when the time comes, or you will suffer the consequences.

Both of these families should ideally be able four weeks old (that is, that’s how long since their first leaves emerged) when it comes time to plant them in the garden. This will put the cucurbits at the stage where they have between two and four of their true leaves (not the cotyledons which are the first two leaves to emerge when they sprout). Any larger than that and transplant shock may set them back significantly.

It should be noted, too, that all cucurbits are not created equally (of course, because that would be simple). Cucumbers and zucchini tend to grow faster than the others – and germinate in cooler soil – so sometimes they can be seeded directly and develop faster than their seedling counterparts. This depends entirely on your climate, so this is where I get to shrug my shoulders and tell you to experiment.

The important thing for the cucurbits when timing their transplantation is soil temperature – not the date of the planting month (though that is in fact true for literally all gardening, in most cases we fudge it). This is another time in which it’s important to know your climate. Your soil should minimally be between 65-75F before planting; the lower end is okay for cucumbers and squash; the higher end is needed for melons.

Brassicas are less worried about the temperature of the soil – frost free is their big ask – but their age is a serious factor. The older they get beyond the four-week mark the more likely they are to experience transplant shock and buttoning. Brassicas also need to be watched very closely when started indoors as they will grow exceptionally quickly – and too much – if exposed to temperatures that are too warm (higher than ~65-70F). This leaves them leggy and brittle and hard to transplant successfully.

As you can see this all adds up to fair bit of planning ahead in order to ensure the success of your chosen crops. This is where a spreadsheet and few minutes of quick math can really help you make the best choices and start your growing season off on the right foot. Below I’ve created the seedling starting schedule that I use – it also includes direct seeding dates and information for the things I don’t start early – it may help you plan this year while you experiment with what works best in your own climate.

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