Every September I start to get emails full of fall gardening questions, and some of them come down to a single decision: do I start these seeds in a seed flat, or do I put them straight in the ground?
It’s a fair question, and the answer has less to do with the season than with how a particular plant builds its roots.
Why some seedlings resent being moved
Plants in the carrot family – carrots, parsley, cilantro, dill, fennel, celery – send down one deep taproot early and fast. The tip of that root is where growth happens. Break it, kink it, or let it spiral around the bottom of a cell tray, and the plant either struggles for weeks or produces the forked, stubby carrot that shows up in every “check out my funky carrots! What happened here?” photo someone sends me.
The UF/IFAS Florida Vegetable Gardening Guide has a column in its planting table that’s easy to skip past: Transplant Ability. Crops are rated I (easily survives transplanting), II (survives transplanting with care), or III (only plant seeds or containerized transplants with developed root systems). Carrots and celery are rated II. Radishes and turnips are rated III. It’s worth a glance as you plan your fall garden.
Root crops are also where the rule gets more interesting than “never transplant a root.” Beets are rated I. They move well if you set them out while they’re small, and their so-called seed is actually a dried fruit holding several embryos, which is why one seed often comes up as a little cluster that needs thinning.
Cilantro and parsley deserve their own paragraph
These two surprised me. Neither one is in the vegetable guide’s Transplant Ability table, and I’d transplanted both for years before I looked closely at why they’re usually recommended as direct-seeded.
Parsley is fairly hard to transplant, so UF/IFAS recommends sowing it where you want it to grow – about a quarter inch deep, sown thickly, then thinned to roughly six inches apart. The other half of the problem is patience. Parsley germinates slowly, and two to three weeks of bare soil is normal. Keep it evenly moist and don’t assume it failed.
Cilantro is best direct seeded for the same taproot reason, and it also has a habit of bolting the moment things warm up. Each cilantro “seed” is a coriander fruit holding two seeds, so seedlings tend to come up in pairs; some gardeners gently crack the husks between their fingers before sowing for quicker, more even germination.
If you do need to start either one in containers – I grow seedlings for programs, so I understand the temptation – use deep cells or biodegradable pots so the whole root ball goes in the ground as one piece. With biodegradable pots, tear off the bottom and any exposed rim at planting, since they break down slower than you’d think. Sow two or three seeds per cell and thin by snipping the extras off at the soil line rather than pulling them, which leaves the survivor’s roots undisturbed. Plant out within about three weeks, before that taproot reaches the bottom and starts circling.
What genuinely does better in a seed flat
Most of the cabbage family transplants easily: broccoli, cabbage, collards, kale, kohlrabi, Chinese cabbage, and arugula are all rated I, as are lettuce and Swiss chard. In early September, that’s a real practical advantage. Our soil is still hot, afternoon storms can beat a seedbed flat, and small seedlings in the open garden get found quickly by insects. Starting these in flats lets you control water and light for the first few weeks, skip most of the thinning, and set out a sturdy plant once temperatures ease off. I grow my fall brassicas indoors under grow lights, though setting them up is a subject for another day.
Where the rule bends
Category III doesn’t mean a crop can never be moved. Read that rating again – it’s saying to sow the seed directly or set out a transplant whose roots have filled the container. It rules out bare-rooting and rough handling, not transplanting itself. Beans, squash, and cucumbers are in that group because their roots are brittle, not because of any taproot, and plenty of us start cucumbers in pots and get a fine crop off them. What makes it work is moving the whole root ball intact – roots knit through the media enough to hold the plug together when you tip it out, but not yet circling the bottom of the cell.
A lot of transplants get hurt before they ever reach the garden. Water seedlings thoroughly about a half-hour before planting, so the media is soaked but drained – dry mix crumbles the moment you tip a plant out of its cell, and the roots come apart with it. Water again once each plant is in the ground to settle soil around the root ball, and check on them daily that first week.
The timing pressure in fall runs opposite to spring. Frost is rarely the limit here – it usually holds off until late November, and most of these crops shrug it off anyway. The squeeze is at the front end, in the heat. A transplant set out in September is trying to build roots while its leaves are losing water fast, and a root ball that got knocked around can’t keep up. Wait out the worst of it or shade new transplants for their first week or two if temperatures are still high.
What to sow directly this fall – and how to keep it alive
Keeping crops well-watered and sheltered from the heat are major advantages of seeding fall crops in containers and transplanting later. So, what about our direct seeded crops, how can we get the season started in the late heat and still have success?
Parsley and cilantro are cool-weather herbs, and that’s the real cue for both. Parsley can go in as soon as the worst of the heat breaks, and it will hold through winter. Cilantro is worth waiting on a little longer, since sown into September warmth it tends to bolt before it gives you much. Once it cools, sow short rows every two or three weeks rather than all at once.
Crops such as carrots, radishes, and turnips can all go in starting in September, but they’ll need help getting through the heat. Germination is the first hurdle – carrots are slow to sprout and need consistently moist soil – and young seedlings can struggle in September heat even after they’re up. A few things that make a difference:
- Sow shallowly and firm the soil so seed makes good contact.
- Water lightly twice a day rather than deeply once.
- Lay a board or damp burlap over the row to hold moisture and check daily so you can pull it the moment sprouts appear.
- Cover your garden with shade cloth – it can help protect newly sprouted fall crops from the late extreme heat.
- Plant a few radishes alongside slower crops. They’re up in a few days and tell you whether conditions are working.
I run both systems every fall – flats of brassicas under lights indoors, carrots and cilantro going straight into the bed. Matching the method to the root is most of the battle.
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