Pricking out (no tittering at the back) is the process of transplanting seedlings from wherever they were sown to their next home. I’ve done a fair bit of reading on this topic recently so forgive me if I go into lecture mode.

When seeds first germinate they typically produce a couple of small leaves, called seed leaves, or cotyledons (Latin for, wait for it…. seed leaf!).

These are temporary leaves that the seedling uses to give a little photosynthesis boost to root growth prior to the proper leaves coming through.  The seed leaves are called that as they exist in an embryonic state in the seed. The seed leaves are a basic affair, similar looking on most plants. Some plants hold on to them, some ditch them once they have some proper leaves. The proper or true leaves develop post embryonically, after germination and usually look very different to the seed leaves. To complicate matters, some plants begin life at germination with a single leaf, like a blade of grass. The differences are explained nicely here.

In the propagation and gardening books I have, there are two schools of thought about when to prick out seedlings.  Some (eg Carol Klein) say that we should wait until the first set of proper leaves comes through, others (including the RHS, Peter Thompson, Christopher Lloyd) that the right time to move them on is as soon as they can be handled, when the seed leaves are out. Others (me) say do it when you have five minutes, but sooner rather than later. Depending on how sausage fingered one is, this can be very soon after the seedlings have appeared and the seed leaves have emerged. There are pros and cons of both approaches (asap vs proper leaves). It’s essentially a trade off between robustness and difficulty of safely untangling the well developed roots of larger seedlings. They can put on roots surprisingly quickly, even when quite teeny.

This one does not have proper leaves yet and is quite small, but does already have a neat little root system. Left for longer those roots and those of the seedling’s neighbours would grow like billio and get tangled up. The risk then is damaging the roots when trying to separate the seedling from the substrate and from eachother. This is particularly true for the sowing method I’m using where 50-odd seedlings are packed into a 7cm pot. In addition, the seedlings allegedly suffer less of a “check” on growth if transplanted as soon as they can be handled. The larger seedlings are also more troublesome to transplant, more roots to damage as they are poked about to get them in the hole prepared for them.

It is easy to get intimidated by the tiny seedlings, they appear to be quite delicate. Even with my large hands, I don’t squish very many. The wee seed leaves are quite strong and provided they are loosened with a dibber or plant label the seedlings come out pretty easily. Another advantage of the vermiculite sowing method is that I’m finding the small seedlings don’t need much encouragement to be free of it, I can almost gently tug them out. Almost.

When transplanted they do look very small and lonely but like wot seedlings do, they soon grow on.

Two in a bed. Small now but they’ll grow on fast.

I had a brief discussion on this topic with Christina and we agreed that it might be interesting to conduct a trial, particularly as the advice is conflicting. More on that in a later post.

Regardless of when you choose to prick out, avoid holding the seedling by anything other than the leaves. I favour a one-leafed grip, but it is also effective to pick up by both leaves by sort of folding them over, I imagine the way you would if you needed to pick up a rabbit by its ears. I’m not sure that you should carry a rabbit like this, probably not. The stem is very vulnerable to fatal damage at this point, easily bruised, and not just from picking it up. When dibbling into the hole it’s important not to poke the roots and stem about too much and not to firm them in too hard, easy does it. Talking of the hole, this can be made with a dibber made for the purpose, a bit of cane, a pencil, a chopstick, a finger, whatever. Make the smallest hole necessary to slip the roots into, which could be quite small.

What to transplant into? Depends how many seedlings there are, how big they are, how much space there is, how much compost you have to spare. This year I have been using half-trays and fitting in 20 or so seedlings evenly spaced. Sometimes I double up and have two varieties in smaller quantities in the same half tray. Occasionally I have used modules and even less commonly, individually in pots, although this is wasteful of both compost and space. I used to prick out all my seedlings into individual pots, and I do like a bench packed with neat rows of individual pots, but I could not propagate in any volume using that method, I just wouldn’t have the space. In the half trays they can grow on a fair bit till ready to pot on, by which time the weather will probably have warmed up enough to start the hardening off process. I may even be able to plant out direct from the half tray, but not really expecting to.

They need watering in, using a very fine rose from above, or by sitting the tray in water for a while. I also like to cover the compost with vermicilite, if I had grit to hand I’d use that, to keep it neat and to make it harder for moss and liverwort to colonise the surface thereby putting the seedlings at risk of damping off and other assaults.

It’s a fiddly process alright, this pricking out, but not difficult or onerous. I find it quite meditative.
I’ll be back, with news of the trial.