Direct Sow Like a Pro: How to Get Strong Germination Outdoors
It’s easy to assume that growing food from seed in the garden is a piece of cake. There are no lights or heat mats, no germination domes or pots or potting soil to worry about. Just make a hole, stick a seed in the ground, and water, right? Well….sort of. While some plants are as straightforward as that, others may need a bit more coaxing to germinate in a nice uniform stand. So next we’ll talk about 5 ways you can improve the germination rate of direct-sown crops.
1) Follow the directions. As a kid I’d often try to make cookies or cakes, then complain to my mother when they weren't coming out right. Inevitably her first question would be, “Did you follow the recipe?” and inevitably I would look away and admit that I’d made some adjustments - maybe I didn't have brown sugar, so replaced it with white, or swapped baking soda for baking powder. “It’s chemistry!” she’d always admonish. And gardening is much the same.
Use good ingredients (seeds, soil, compost), follow the directions on the packet, and the plants will largely take care of themselves. This is especially true as regards planting depth. Large seeds need to be planted deeply to ensure good seed-to-soil contact, darkness, and adequate moisture. Small seeds often need to be planted shallowly because light is part of their trigger to germinate. For small seeds like onions, some growers cover them with just a light sprinkling of sand to ensure they are covered but still have access to light.
Timing is important too. If the packet says to direct sow seeds after all danger of frost has passed, wait until that date. Many gardeners have been tricked by unseasonably warm springs, only to feel intense dismay upon hearing of a frost advisory just after planting. Spring is fickle, and a week in the eighties is no guarantee that it will stay that way. Remember that the warmest, clearest, sunniest days are the ones most likely to be followed by frost. Even the hardiest varieties are vulnerable just after germinating, and should be protected with row cover in the event of frost.
2) Ensure constant moisture. Just like transplants started indoors, the soil must never dry out while seeds are germinating. This can be challenging outdoors, as an ordinary day might begin calm, but then be ferociously windy by noon, and calm again by dusk. It’s not uncommon to arrive home from work to find parched seedlings even when it wasn't a particularly hot day. The wind is just as drying, if not more so, than the sun—so it’s best to check the weather every morning, and if it’s forecast to be warm or windy, water thoroughly before you head out for the day.
But there's another side to this coin - keeping the soil wet won't do much good unless you also make sure the seeds are making good contact with the moist soil. Before sowing, rake out the bed so that it forms a relatively smooth and stone-free surface. You don't need to pulverize the clumps of soil (that will make crusting worse) but creating a flat surface will make it easier to form furrows that are the correct depth, while providing fine-textured soil that will make good contact with the seed.
3) Water proportionally. What do I mean? I mean that in order to germinate, different seeds need different amounts of water. It’s always a good idea to make sure the top few inches of soil are thoroughly soaked after planting. But large seeds, like peas, beans, nasturtiums, and squash need a LOT of water to germinate—enough that their entire seed coat can absorb it like a sponge, double in size, and have enough left over to feed the growing roots and shoots. So make sure those large-seeded crops are watered thoroughly and deeply every day that it doesn't rain during germination.
4) Keep it covered. Smaller, more delicate seeds like carrots and lettuce will germinate poorly if any crust forms on the soil surface. One thing I've learned by now is that crust in baking is good, but crust in gardening is bad news. Crusting usually happens when you water heavily initially (which compacts the soil surface), and then it gets hot or windy and this dense layer dries out, with your seeds suspended somewhere inside, unable to break through the hardened soil.
To prevent this scenario, lay a piece of lightweight row cover over the bed right after planting. The row cover will help reduce evaporation from the soil surface, retaining moisture and preventing a crust from forming. As soon as the seeds have germinated, remove or raise the row cover to give them room to grow.
Alternatively, mulch. A bale of straw mulch goes a long way, and will dramatically reduce the time spent weeding on hands and knees. Before direct sowing, mulch to a depth of at least 4”, then make furrows in the mulch and soil below, plant your seeds, and water well. The mulch will serve many useful purposes—preventing a crust from forming over the germinating seeds, keeping roots cool and moist, discouraging weeds, and adding organic matter to your soil.
If you’re planting a cool-season crop like lettuce, kale, spinach, or peas in warm soil, as often happens when planting in midsummer for fall crops, you can use a little trick to cool down the soil before planting. Simply cover the bed with cardboard for a week prior to planting. The cardboard cools the soil by shading it and reducing evaporation. After planting, replace the cardboard over the bed to keep the soil cool during germination, lifting it daily to water and check for seedlings popping up. Be sure to remove the cardboard as soon as the seeds have germinated.
5) Don’t sow too thickly. Many gardeners, even experienced ones, are guilty of sowing too much seed for the available space. It might seem like “crop insurance” – maybe the seed was a few years old, or the conditions seem challenging – so you think “What the heck, it can’t hurt.” Well I’m here to tell you otherwise--sowing too thickly can turn into a major headache.
Thinning is a time consuming task and must be done when seedlings are still very small – think wispy 1” tall carrots that must be distinguished from grass, horsetail, and any other weeds, then carefully culled so that they’re no closer than 1” apart. Proper spacing of carrots and beets is essential for good yields--each root needs room to develop, and foliage needs room to grow thick and lush to support root growth.
But by the time you've finished thinning a 20-foot bed with three rows in it, your back, knees, eyes and fingers will be complaining. So why don’t people avoid this whole situation and simply plant the seeds 1” apart from each other? That part is still a mystery to me. My guess is that it's simply easier to sow seeds thickly. But given the additional work this makes later, I think precision seeding is a better way to go. The lesson is, mulch, take your time and seed like a minimalist—it's more economical and a lot easier than the alternative.