Zucchini and marrow are classified as cucurbit (Cucurbitaceae) vegetables. The cucurbit family includes cucumbers,  summer squash (zucchini), winter squash (hubbard, acorn, spaghetti, kabocha, butternut, buttercup delicata), pumpkins, melons, and gourds.

Since all of these plants share a common ancestor, they all have very similar growing needs and are prone to similar problems.

While they are quite similar, there are some key differences, so to ensure best success so we've broken these into separate articles for easier instruction.

Summer squash nutrient values vary by cultivar but are generally high in vitamin C, B6, folate and riboflavin. Check here for detailed information from the USDA National Nutrient Database for Standard Reference. 

The Canadian Food Guide recommends that roughly half of the food on your plate should be fruits and vegetables.

Zucchini and marrow are a warm season plant that need between 48 and 100 days to maturity, depending on the type. If direct seeding, grow cultivars that mature in 80 days or less. Summer squashes with longer days to maturity should be transplanted.

They can be seeded or transplanted once the soil is warm (at least 18°C).

If you live in the far north, grow zucchini as seedlings. Seedlings can sometimes be purchased from a local greenhouse.

Starting your own zucchini plants from seed

• Zucchini do not like root disturbance from transplanting, so it's important not to start seedlings too early. Seedlings should only be 10-14 days old before planting out (cotyledons have emerged along with only one or two true leaves).  Larger transplants will experience transplant shock when they are planted outdoors. Plants will not grow for several weeks (or at all) depending on the level of transplant shock they experience. See our video below.
• Start seedlings about 2 -3 weeks prior to transplanting out. You can transplant seedlings as soon as daytime and nighttime temperatures are warm at least 18°C, about 2 weeks after your last average frost free date. For example, in Wollaston Lake (northern Saskatchewan) your plant out date is June 5, so start your seedlings around the first of June for planting out around June 20.
• Jiffy-7's are good for sowing seeds because there is less root disturbance when planting. Soak the Jiffy-7's for 20 minutes in warm water to fully hydrate and expand them. Once they are planted, cover with plastic or a dome and do not water. Remove the plastic once seeds have germinated. 
• Another way to reduce root disturbance is to use home-made newspaper pots or peat pots. Fill them with a soil-less mix that contains peat or coir and vermiculite and/or perlite. (Both of these types of pots can be planted directly in the soil, but be sure to bury the rim of these pots. Otherwise the rim acts as a wick and will dry out your seedling.)
• Sow 2 seeds 1 cm deep per JIffy-7 or container and then thin to the strongest plant after they have grown their first set of true leaves. 
• Zucchini and other summer squashes prefer warm soil. At 24°C, seeds will germinate in 5 or 6 days. Use a heat mat if you have one, or place pots in a warm spot like the top of the fridge for germination.
  
• Take care not to over water your seedlings. Soil should be moist like a damp sponge, but not soggy.
• Place seedlings under lights after germination, which is crucial for the growth of healthy seedlings. seedlings require a minimum of 14 hours of light each day.
  
• Leave a fan blowing on your young seedlings as they grow to help to grow heartier plants and to reduce some seedling diseases. Research has shown that stem diameter can be increased by providing seedlings with constant air movement from an oscillating fan – or by lightly brushing seedling tops with a tea towel or stick at least 20 times daily.
• For more details, check out our article on growing your own seedlings.

The ideal zucchini transplant:

• has no more than two sets of true leaves. The first leaves that grow are not true leaves. They are "seed leaves" called cotyledons and are round. All leaves that grow after these are true leaves.
• is dark green in color.
• has a good root system but is not root-bound (tight, hard ball of roots) or has lots of roots growing out of the Jiffy-7.
• has a stem that is strong and sturdy. The internodes (spaces between leaves along the stem) will be small.  seedlings that are too tall will tend to break and dry out more easily once planted out into the garden.
• Fertilizing recently planted seeds or young emerging seedlings is not recommended. Start fertilizing a few days after they have been planted out in the garden using 20-20-20 water-soluble fertilizer once or twice a week. Mix according to label directions.

Harden off seedlings prior to planting out by moving them outdoors into a sheltered, frost-free location at least 3 days prior to transplanting.

Don't forget to label what you planted. It's also helpful to draw a map to help you track planting locations and success each year. This information is critical if you're rotating your crops to help prevent insect and disease issues.

Timing

• Zucchini and other summer squashes may be direct seeded in the garden or planted as seedlings. See our transplants tab for tips on growing or purchasing your own transplants.
• You can transplant seedlings as soon as daytime temperatures are above 18°C. For example, in Wollaston Lake (northern Saskatchewan) your plant out date is June 5, so start your seedlings around the first of June for planting out around June 20. Saskatoon's plant out date is around May 13, so start your seedlings around May 7 for planting out at the end of May or beginning of June.
• Transplants must be hardened off before transplanting outdoors. Winter squashes do not tolerate cool soil or air temperatures.

Direct sow instructions

• One or two summer squashes are usually enough for the average family of four.
• Sow 3-4 seeds 2 cm (1″) deep and 90cm-120cm (36-48″) apart.  Thin to the strongest seedling. 

Planting instructions for seedlings

• When planting, cover the entire transplant “plug” or seed ball with soil to prevent the plant from drying out.  If using newspaper pots or peat pots, make sure they are quite moist before planting and remove the rims of the pots. Exposed rims, peat or coir within the plug will act as a wick, drawing water away from the transplant and drying out the root ball. 
• Try not to disturb the roots when planting.
• Seedlings should be spaced 25 cm apart within the row, allowing 90 cm between rows.
• Water the transplants in with 10-52-10 soluble fertilizer, mixed according to the directions on the label. This is only done once, to encourage good root development. See the "Care Once Planted" tab for how to fertilize for the rest of the growing season.

Cutworm prevention

If you have had cutworm problems in your garden, place a collar around your seedlings right after planting. Make collars out of toilet paper rolls, or any tin can or plastic container such as a yogurt container with both ends removed. Insert the collar at least 5 cm in the ground to prevent cutworms from feeding on the stems of your seedlings.

There are a wide variety of summer squashes which come in different shapes (long and narrow, round, pattypan) and colours (green, almost black, white, yellow, gold). Most of them are 'bush' types. 

• Yellow summer squash - long, thin fruits that can be smooth or warty, straight or crooknecked.
• Zucchini types are also long and cylindrical, often dark green also lighter, yellow or even white.
• Scalloped or patty pan squash like disc-shaped UFOs. Scalloped edges - from greenish to yellow to white.
• Mideast or Cousa fruit is shorter and thicker than zucchini, usually with a pale green skin.

Here are cultivar recommendations from the North Dakota State University Cultivar Trials, as they share a similar prairie climate and soils. You may download their list here:North Dakota State University Vegetable Cultivar Recommendations for 2021

• Crookneck: Gentry, Sundance
• Scallop: Flying Saucer, Sunburst
• Straightneck: Fortune, Multipik, Slick Pik YS 26, Zephyr
• Zucchini: Cashflow, Desert, Easypick Gold, Gold Rush, Green Machine, Green Tiger, Payload, Portofino, Raven, Spineless Beauty.

The following cultivars are recommendations from the University of Saskatchewan vegetable program field trials which were conducted from 1989 through 2016. Although this information is no longer current, some may find it useful.

• Green zucchini: Ambassador, Bobcat, Chongma, Dividend, H.N. Zucchini, Jemmy, Onyx, Payroll, SE 104, Spineless Beauty, Striatod'Italie, Sungreen, Super Select
• Yellow zucchini: Butterstick, Gold Finger, Golden Rod
• Specialty: Alexandria, Basima, Geode

Summer squashes like zucchini should have about 2.5cm of water per week early in the season.  By mid-July, provide 2.5cm of water, twice weekly. Dry soil may result in smaller squashes.

Apply soluble 20-20-20 fertilizer every week prior to fruit set. Increase fertilizing to twice a week after fruit set.

Pick weeds as they appear.

To conserve soil moisture and reduce weeding, apply a thick layer of mulch around your plants, whether in the garden or in a container. Ensure the mulch is not resting against the stems of the plants.

Summer squashes benefit from growing in plastic mulches, supported plastic tunnels or crop covers.  Crop covers and tunnels must be removed as soon as flowers appear so that bees and other pollinators can pollinate flowers.

Cucurbits have both male and female flowers on their vines.  Male flowers are the first flowers to appear on the plant.  It is normal for some of these initial male flowers to fall off – don't be alarmed.  Female flowers appear 7-10 days after the male flowers start to appear.  The female flowers are identified by what looks like a small fruit where the stem meets the flower.  This ‘small fruit’ is missing on the male flowers.

Summer squashes such as zucchini are not suited to fall seeding.

Summer squashes such as zucchini are best grown as transplants in the far north. Direct seed only if the soil is very warm. To pre-warm soil, cover soil with a layer of clear plastic 2 weeks before planting. Secure the edges to keep the plastic from blowing away. Remove the plastic after planting.

Zucchini do well in containers. Black or dark coloured containers help keep the soil and root system warm.

Zucchini benefit from black plastic mulch, row covers and clear low plastic tunnels to keep the environment around the plants warm. 

See our preservation section for more videos.

An early-maturing, compact, bush type of zucchini would work best in a container, such as: Raven,  AAS Peter Pan hybrid, Goldy Organic hybrid, Gold nugget (orange)

Saving zucchini seed is tricky because certain squashes can cross pollinate:

• Delicata, acorn and sphaghetti are related closely enough to zucchini and pumpkin that they can cross pollinate: all are Cucurbita pepo.

All squashes have separate male and female flowers. The female flower requires pollen in order to produce fruit, but the pollen can come from other compatible species of Cucurbita as described above. Pollen is moved by insects such as bees, bumblebee, hoverflies, ants and others.

Here is an example of cross-pollination: If you grow acorn squash in the garden and it is pollinated by a nearby zucchini, this year's fruit will still look like an acorn squash. But if you harvest the seed from that squash, the seed will contain genes from both the zucchini and the acorn squash. If that seed is grown next year, the resulting fruit will look very different – with a combination of characteristics of both parents. This is called a hybrid.

Summer squashes need to be isolated from related Cucurbit species in order to get seeds that will produce the same type of winter squash next year. Commercial seed producers grow acres of different curcubita plants for seed production. What they do is group like with like in very separate areas – with at least 800 or more feet of separation to prevent cross-pollination. This is not feasible in urban areas but there is a solution.

Controlling pollination

If you plan on saving seeds from a heritage or open pollinated summer squash in your home garden, you'll have to control pollination. Here's how:

• It’s best to do this early in the morning as cucurbit flowers open early and before bees and other pollinators are active.
• Use a small brush or cotton swab to dab the center of a male flower – these are the flowers with a large anther in the middle which contains the pollen. The pollen will stick to the brush as it would on a bee.
• Next, transfer the pollen to the centre of one or more female flowers from the same plant. Female flowers lack an anther and have what looks like a small swelling just beneath the flower. Or, you can simply pick a male flower and gently touch the anther to each of the female flowers you want to pollinate. 
• Next, cover the pollinated flower with a muslin or paper bag and secure it so that insects cannot access the flower and accidentally introduce different pollen. The bag can be removed once the fruit starts growing larger. 
• Mark the fruit with a piece of yarn so that you remember which one is the controlled cross.

How to save seeds

Harvest seeds from overgrown and over mature squashes because their seeds tend to be fully mature. Carefully cut the squash in half and scoop out the seeds. Wash seeds well to remove as much of the stringy flesh as possible. Spread on a dish towel on a tray and allow to dry completely. Drying can take up to a week.

 
How to store seeds

Vegetable seeds can keep for several years if you store them properly. Seeds should be stored in a cool, dry, dark place. Moisture, heat and light can cause seeds to sprout or rot.

• Place your seeds in envelopes or make your own envelopes out of foil or waxed paper. Label with name of the seeds and the date (month and year) you harvested them.
• Place your envelopes inside an airtight container. To help keep seeds dry, place about a tablespoon of dry powdered milk in a paper towel or piece of cloth, secured with a twist tie or piece of string. The powdered milk will absorb humidity and keep seeds dry inside the airtight container.
• Put the container in the refrigerator. Do not store seeds in an unheated shed or garage. These places are either too moist and/or too cold for seed storage.

Use a sharp knife or pruners to cut the squash from the stem. Leave at least 3 cm of stem intact to avoid problems with stem end rot.

Be careful when harvesting zucchini and other tender summer squashes. They damage easily.

Zucchini and other summer squashes have a fairly high respiration rate, harvest early in the day and keep them in the fridge until you use them.

Coming soon

• Download entire series here

Common problems include powdery mildew and pollination problems.

An interesting archeological paper about early cucurbit use by Indigenous peoples:

Additional evidence for early cucurbit use in the northern eastern woodlands east of the Allegheny Front

More research:

Organic cucurbit production - Dalhousie University

Managing cucurbit disease - Michigan State University