Zucchini, summer squash, gourds, baby marrow, corgettes—whatever you call it—pound for pound, nothing produces more cropage than these green beauties. Relatively fast-growing, zucchinis can actually be direct-sown right into your garden in all but the coldest climates.
I always choose to start my zucchini seeds manually indoors due to mild climate. And there’s a couple of reasons why, which we’ll get into today. This is part one of a two-part series where we’ll dive into the wonderful world of the famous summer squash.
Growing Zucchini
Zucchinis are a descendant from squashes, a group of plants that are native to Mesoamerica (Mexico and northern parts of Central America). These exciting new crops were first brought back to Europe by those early colonizers. It wasn’t until the 1800s that zucchinis were first bred in Milan, Italy, and then finally making their way back to America in the 1920s. And although used almost exclusively in savory cooking, zucchinis are actually a fruit—a berry to be exact!
While many seem to think that zucchinis practically grow themselves (and really, they’re not all that wrong), with a little assistance and guidance from the diligent gardener (you and I), these guys can achieve legendary status in our gardens.
Before we get planting though, I do want to touch on why I start my zucchini seeds early indoors when I actually don’t have to. Full disclaimer: you can actually direct sow your zucchini seeds right into your spring garden if that’s your preferred method of planting and you’re in a pinch.
Here's how:
Plant your zucchini seeds in moist, rich compost-infused soil roughly two weeks after your last spring frost. Ideally, your soil temperature should be in the sixties. Plant the seeds about one inch deep, flat, and two to three seeds in close proximity. Then thin to the strongest plant 10 to 14 days after germination, as zucchini plants themselves need about two feet of spacing between each plant and three feet between each row. Water moderately but never let the plants dry out, and of course, grow these guys in full sun. Under those conditions, zucchinis are going to sprout in 7 to 14 days and grow to the size of our transplant within a month to 6 weeks.
Simply put, zucchini plants don’t need that head start that our tomatoes and peppers do, so why bother? Other than being able to harvest zucchini fruit in May instead of July, I actually have two reasons why I start them early indoors. In fact, any crop that I can start from a plug or transplant early, I will. I avoid direct sowing unless it is absolutely necessary (I’m looking at you, carrots and beets).
Now, first sowing separately, regardless of when, buys me time. I look at my garden as a 12-month plan with overlapping planting, crops, maintenance, and harvests. As such, if I can grow a plant for the beginning portion of its life under controlled conditions indoors or in the greenhouse, I can grow something else in that spot until it’s ready to plant. Two crops are always better than one!
Leveling up even further, direct sowing will take your plants right to the end of summer, but planting a head-started zucchini in April could mean your harvest is done in June, allowing you to plant yet one more summer crop after the last zucchini is picked. Most certainly, three crops are better than one.
The other reason, as if we needed one, is selection. By planting and growing more seeds than I need, I can be picky and choose the best of the best when it comes to the plants that make it into the starting lineup. Summer garden space might as well be waterfront property on Mars—its value cannot be readily defined or measured, but most certainly, it’s going to command a higher price than a few seeds and a bit of soil that might cost pennies.
Growing Zucchini Early
So, if you’re still here, it means you want to start your zucchinis early. Let’s dive into it!
Two weeks before your last spring frost, begin to think about planting your zucchini seeds indoors. Zucchinis can be sown in two ways: the standard plug trays (tried and true, never let you down), and they won’t start here. Alternatively, because these guys grow so fast, we can sow them in standard 4-inch nursery pots directly—or better yet, biodegradable paper cups like these ones here, using a technique that I stole from my watermelon obsession.
Planting in paper cups like this is great because transplanting into the garden can be done by directly digging the cup into the soil all in one piece. While this kind of planting is really designed for plants that don’t like their roots disturbed, zucchinis aren’t all that finicky like my watermelons are. Nonetheless, it’s a fantastic way to start them and more than enough room to let them grow until the exact moment that there’s a vacancy in your spring garden.
Pre-soak your soil for about two hours before planting, either way. I should point out that if you used a paper cup or any other non-standard, non-nursery container, you need to make sure the bottom has drainage holes. These zucchinis, like every other plant in our garden, will die if they are left in standing water.
Indoor seeds are planted one inch deep, just like direct seeding. They can be placed inside a suitable depression or right on the surface of the soil and simply pushed down to the desired depth. A suitable seeding mixture should be used for the soil you use; This time of year, it’s easy to find.
Zucchini, like most seeds, have an optimal range for germination (80 to 90 degrees Fahrenheit). Indoors, we can accomplish this by either a low-wattage heat mat or the heat given off by our grow lights from above. In this range, zucchini seeds will sprout within a week and they come up with gusto. As soon as all the seeds emerge, before any trace of true leaves appear, take them off any supplemental heat and give them as much light as possible. Zucchinis grow fast, and the possibility of creating a giant first long internode (becoming long and leggy for you non-plant nerds) is very high. Temperatures in the 60s and 70s with 10 to 16 hours of full-spectrum light is really the goal here.
If you’ve started your zucchini seeds two weeks before your last spring frost, they’re going to have a month or more in your care before you can unleash them in your outside garden. They’re going to need food, which we can actually supply in two ways. The first is to simply liquid feed a general organic balanced fertilizer using a 5-10-10 or a 5-10-5. Seaweed extracts or fish emulsion mixes seem to work really amazing for this, and they’re relatively inexpensive. Not only that, they get diluted a lot, so a little goes a long way.
The second is actually replant your zucchinis into larger pots, which is highly recommended if you went the plug tray route. Replanting these young seedlings gives us the chance to surround them with fresh, new, and rich potting mix. Seedy mixes are quite often nutrient-poor for those delicate seedlings. But just look at these guys now—within a couple of weeks after germination, your young zoos are going to be searching for food.
Amend your standard potting mixes with a granular organic fertilizer or make your own blend with things such as alfalfa meal, canola meal, rock phosphate, Epsom salt, bone meal, and even dried crushed seaweed. Whatever you use, keep it mild and keep it low dose. You can always add more later. Replant your zucchinis using the standard potting methods. I like to fill my pots first, soak them good from below for about two hours, then make a hole for the plant and place it right inside. You can do hundreds of plants in short order this way, and it really does minimize the handling of those delicate seedlings.
Still, keep those new transplants relatively cool, you know, room temperature or even cooler, but give them as much light as possible. If you were buying zucchini starts to directly plant into your garden, we’re roughly at that stage right now. Good stuff!
Stay tuned for part two in this series, where we plant the zucchinis out into our spring garden, setting them up for maximum summer success and, of course, the harvest.
