Your zucchini seedlings are patiently waiting in their little pots to be transplanted outdoors. They have already developed their first true leaves and you start wondering if the time has arrived to move them to their new location under the sun. Are you indecisive about the timing, the right location or are you simply looking for tips and guidance on how to transfer your seedlings outside? Learn all you need to know about moving your zucchini seedlings outdoors!
Zucchini (Cucurbita pepo) is a type of summer squash from the family of Cucurbitaceae, which also includes cucumbers, melons, squashes and pumpkins. Zucchinis are a very easy crop to grow in temperate climates. In fact, once a zucchini plant starts producing, the harvest can get a bit overwhelming. The young fruits of zucchini are commonly consumed as vegetables but the flowers are also edible.
In my recent blog post, I provided you with a step-by-step guide on how to start zucchini indoors using the zip lock method. It has been a month since then and, believe it or not, the seedlings are now ready to be transplanted outdoors (I told you the zip lock method would speed it up!). In this post I respond to the three most commonly asked questions related to transplanting zucchini seedlings outdoors: When, Where and How.
- When to transplant zucchini seedlings outdoors
- Where in your garden plant your zucchini seedlings
- How to transplant your zucchini seedlings
When to transplant zucchini seedlings outdoors
First, how do you determine that your seedlings are ready to be transplanted outdoors? Once your zucchini seedlings develop two to three true leaves, they are ready to withstand the harsher outdoor conditions.
What are true leaves? True leaves are the second set of leaves growing on seedlings of plants. They are preceded by cotyledons, the first leaves to appear from the germinated seed. While true leaves are essentially a mini-version of the adult leaves, cotyledons have quite a distinct appearance from the adult leaves.
In the plant kingdom, cotyledons occur in two versions: monocots (one cotyledon present) and dicots (two cotyledons present). I previously referred to monocots and dicots in my post on The Science behind Eggshell Fertilizer as a way to classify plants with respect to their calcium needs. Zucchini belong to the class of dicots and as such their cotyledon will appear in a pair, followed by the first true leaf as you can see in the picture above.
Why to wait for a few true leaves before transplanting your seedlings outdoors? Both cotyledons and true leaves contain chloroplasts and allow for photosynthesis, which is the primary source of energy for plants. Cotyledons store nutrients, perform photosynthesis and provide all nutrients needed for seedling growth until the first true leaf becomes a significant exporter of photosynthates.(1) This means it is possible to transplant seedlings prior to their first true leaves appearing. However, once a few true leaves are established, plants are generally less delicate with a developed root ball, which can hold the planting soil together. The true leaves are simply a good indicator of the plant’s maturity and endurance.
Another important thing to consider when transplanting your zucchini seedlings outdoors is the timing with respect to your climate. Living in zone 6, I usually transplant my zucchini seedlings outdoors in the second half of April but this might be way too early for many locations with colder climates. You can check Plant maps, a free online tool that provides a last frost date based on indicated zip code or location.
Since zucchini are a warm season crop, earlier does not necessarily mean better. Even if frost is not an immanent danger, cold temperatures will certainly slow your seedlings’ growth rates. Zucchini should not be transplanted outside until temperatures remain consistently above 15°C (60°F). Keep an eye on local weather forecasts and if serious cold weather is predicted, hold off on transplanting zucchini until temperatures are more agreeable.
Where in the garden to plant your zucchini seedlings
If you have never had zucchini in your garden, you will be surprised how large the plants get and how fast they grow. Hence, your zucchini plant will need quite a bit of space. Choose a spot of at least 60 x 60 cm (2 x 2 ft) per plant. As a reward, you will get your desired zucchini harvest in less than 60 days from planting.
To produce, zucchini need full sun, which corresponds to six to eight hours daily. You should try to avoid planting zucchini near large trees and bushes. They also prefer well-drained but consistently moist soil.
If you already had zucchini in your garden, try to avoid planting them in the same spot as last season. Crop rotation helps to avoid the spread of diseases typically occurring in zucchini, such as powdery mildew. Since every plant has slightly different nutritional needs, rotating your corps will also prevent the depletion of specific nutrients in your soil.
Finally, think of crops that are going to neighbor your zucchini seedlings and try to select good companion plants to grow in their proximity. The idea behind combining crops that grow well together is to allow mutually supporting plants to help each other grow as a community. The best companion plants for zucchini include roots such as beets, onions, lettuce, beans, sunflowers, tomatoes, eggplants, peppers or herbs such as basil, parsley and oregano. You can also check the app From Seed to Spoon to discover more suitable companion plant recommendations for zucchini.
How to plant zucchini plants
This step-by-step guide will guarantee you a great zucchini harvest in no time:
- Prepare your soil: Ideally a few weeks prior to transplanting your zucchini, prepare the soil in the spot that you have chosen to plant your zucchini seedlings. This consists of tilling the soil, adding lots of organic matter in a form of compost and aged, composted manure as zucchini are heavy feeders that thrive in rich soil.
- Harden your seedlings: Although I usually skip this step because I grow my seedlings on a balcony, those who keep them indoors should definitely expose them to the outdoor conditions for a few days prior to transplanting, always for a few hours at a time.
- Measure: As explained earlier, zucchini should be spaced at least 60 cm apart (2 ft) but ideally more. Measure how many seedlings can you fit into your chosen garden patch.
- Transplant: For each seedling, dig a small hole of about 5 cm (2 in) deep. Gently turn over your pots while trying not to disturb the root balls of your seedlings as you transfer your seedings to the soil. Place them in the prepared holes, cover up with soil and press around to secure good contact of the soil and roots.
- Water: After transplanting, water your zucchini seedlings generously. Continue to provide your zucchini plants with consistent moisture, ideally every two to three days. Because disease spreads easily across zucchini leaves, you should always water zucchini by directing the stream at the soil near the stem and not on the leaves.
A small tip Once zucchini start producing, you can get a bit overwhelmed by the amount of zucchini you get from one plant. In addition, zucchini are so easy to grow and the fruits get large and seedy really fast. This is why I do not recommend planting more than five plants per family of four to five people in each season (even then you will still have plenty of zucchini to share with friends and neighbors).
I hope the transplant is a great success and let me know how your seedlings are thriving outdoors in the comments down below.
Sources:
1. Shi Y et al. (2020). Similarities and Differences of Photosynthesis Establishment Related mRNAs and Novel lncRNAs in Early Seedlings (Coleoptile/Cotyledon vs. True Leaf) of Rice and Arabidopsis. Front Genet, 8;11:565006. https://doi.org/10.3389/fgene.2020.565006
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