From late spring throughout the fall, summer squash can provide a ridiculously-large harvest. This ample producer just keeps churning out more and more produce!
It’s so prolific that there’s a National Sneak A Zucchini Onto Your Neighbor’s Porch day in the USA. Whether it’s pattypan or zucchini, yellow crookneck, or something else, summer squash delivers. And oh, does it keep on delivering all summer long.
Happily, this low-calorie, vitamin-packed food is also delicious. It can be used in salads, as a vegetable side, baked into breads, and even candied. Eaten raw or cooked, it has a mild flavor that works well with both savory or sweet applications.
And did I mention it produces a lot of food? Because oh, does it produce a lot of food. Why spend money at the market when you can simply grow your own? Let’s talk about how to do it!
Good Products At Amazon For Summer Squash Growers:
- Garden Safe Neem Oil Extract Concentrate
- Safer Brand Yard & Garden Spray
- Harris Diatomaceous Earth Food Grade
- AgFabric Floating Row Cover
- Garden Safe Slug & Snail Bait
- Monterey Liqui-Cop
- Surround WP
- Burpee Organic Bone Meal Fertilizer
Summer Squash: Quick Care Guide
|Common Name||Summer squash, zucchini, cousa squash, pattypan squash, scalloped squash, crookneck squash, yellow squash, and many other cultivar names|
|Scientific Name||Cucurbita pepo, Cucurbita moschata, limited number of Cucurbita maxima species|
|Days to Harvest||40-65 days depending on variety|
|Water||Consistent water, at least 1” per week|
|Soil||Rich, well-draining soil|
|Pests||Aphids, cucumber beetles, squash bugs, squash vine borers, snails & slugs|
|Diseases||Powdery mildew, downy mildew, sooty mold, squash blossom blight, cucumber bacterial wilt, cucumber mosaic virus, squash mosaic virus|
Summer Squash Vs. Winter Squash: What’s Different?
The major difference between summer and winter squashes is storability. Summer squash typically has a softer rind and is best eaten when young and fresh. Allowing it to grow to epic proportions and to develop mature seeds makes it less appetizing. We love our summer squashes when they’re tender, not woody.
By contrast, the flesh of winter squash tends to be much firmer, and the rind much more solid. It holds up well to long-term storage. That thicker rind helps protect the fruit from spoilage as long as it’s kept dry and cool.
Summer squash can also be harvested sooner than winter squash. As soon as the fruit is the right size, you can pick it and eat it! Winter squash will achieve its size, but then needs more time to mature on the vine. It slowly develops its natural sugars and flavor.
Botanically speaking, most summer squash is Cucurbita pepo subspecies pepo. There are a few summer squash in Cucurbita moschata and Cucurbita maxima species too. But the latter two species are dominated by winter squash.
Recommended Summer Squash Varieties
Summer squash may all be closely related, but we recognize four distinct varieties. The flavor of all types is similar, but the growth habits vary. Here’s a breakdown of the different types and some recommended varieties!
Ever-present, zucchini is the king of many people’s gardens. Typically green in color, there’s also yellow zucchini and white zucchini. These produce cylinder-shaped fruit which is easy to slice. It’s good raw or cooked.
- Burpee’s Best: 40 days. Spine-free vines create luscious 6-8″ dark green fruit. Good early harvest.
- Chiffon: 42 days. Light yellow zucchini with pale white flesh, very tasty with excellent texture.
- Dunja: 47 days. Dark green, straight zucchini. Intermediate resistance to powdery mildew, mosaic viruses, and more.
- Cocozelle: 48 days. A deep green zucchini streaked with light green stripes. Italian heirloom that can reach 10-12″ long.
- Costata Romanesco: 52 days. Long, ribbed produce with medium-green striped skin, lightly scalloped when cut across the fruit.
- Italiano Largo: 59 days. Deeply ribbed, long and thin fruit. Few seeds even if they get large. Extremely flavorful!
- Green Tiger: 60 days. Beautiful dark and light green striped zucchini with 8″ cylindrical fruit.
- Black Beauty: 63 days. A classic and popular zucchini with dark green skin and white flesh. High in vitamin A!
- Meot Jaeng I Ae: 65 days. Technically this is a Korean summer squash, but it falls into the broad zucchini category. Delicate soft texture.
Yellow Squash Varieties
Bright yellow in color, these yellow squash varieties may be lumpy or bumpy. The neck may be crooked or straight in growth habits, but one thing is for certain: they’re tasty!
- Fortune: 39 days. Smooth, pale-yellow fruit with a 6-7″ eating size. Extremely heavy producer, you’ll have a fortune in squash!
- Dixie Hybrid: 41 days. Smooth-skinned yellow crookneck, bright lemon yellow color. Highly productive.
- Golden Summer: 42 days. A crookneck with character, this warty and bumpy squash turns a deeper yellow as it matures.
- Butterstick: 50 days. This hybrid produces a yellow zucchini-type plant with a straight-neck squash. Bright yellow and firm textured.
- Gold Star: 50 days. Beautiful yellow crookneck squash with high yields. Harvest at 4-6″. Resistant to mosaic virii and powdery mildew.
- Early Prolific Straightneck: 50 days. Uniform lemon-yellow squash. 1938 heirloom with firm flesh and great quality.
Scalloped Squash Varieties
Little delightful discs! Scalloped squash are often called pattypan squash, and they’re almost flower-shaped. These tasty treats are great whether harvested as baby squash or full-size. If you’re looking for a change from traditional squash, these are fantastic.
- Scallop Yellow Bush: 49 days. Flat, round fruit in a bright yellow hue. Good stuffing squash!
- Early White Bush: 50 days. White, scalloped disc-shaped fruit! 1800’s heirloom. Good for patio growers.
- Peter Pan: 50 days. Miniature patty pan type, 1-3″ fruit. Sweet flavor on early-bearing plants.
- Sunburst: 52 days. Cone-shaped patty pan in a bright butter-yellow with a green blossom end. Great as baby squash or full-sized.
- Gelber Englischer: 60 days. Flat-topped fruit with a bulbous base that ranges from lemon yellow to almost pumpkin-orange. Good in cool climates.
- Benning’s Green Tint: 63 days. A pale green scalloped squash. Fruit best at 2-3″ in diameter.
Cousa Squash Varieties
Mideastern squash like Cousa have a shorter but much thicker fruit. These are often called ball zucchini, and may be green, yellow zucchini, or pale white in color. Some of them have streaks along their sides when fully mature. They’re a nice variation from the more slender varieties.
- Desi: 40 days. Pale green baseball-sized fruit with a nutty, rich flavor. Heavily productive!
- Round Zucchini: 45 days. These heirlooms are mid-green with darker streaks and pale speckles. Great at 3-4″ diameter. Flower to fruit in a week!
- Rotem: 47 days. Stocky, marrow-type squash with light green skin. Very robust plant, easy to harvest.
- Cue Ball: 48 days. Pale green fruit with subtle white flecks, very productive with 2-3″ fruit. Resistant to mosaic virii and powdery mildew.
- Magda: 48 days. Sweet and nutty taste. 3-4″ long at harvest, used for stuffing, stir-frying and pickling.
- Ronde de Nice: 50 days. Nutty flavor with tender flesh. Harvest at 2-3″ in diameter. Beautiful mottled green coloring.
- Eight Ball: 50 days. Deep green and perfectly round, shiny fruit. Delicious sliced on a burger. 2-3″ diameter harvest.
- Summer Ball: 50 days. A golden version of eight ball with an open bushing habit. Less prone to blossom end greening.
- Green Eggs: 50 days. 5″ long oval squash, perfect for grilling. Beautiful dark green flesh and very tasty!
- Teot Bat Put: 65 days. Nicknamed avocado squash because of the shape, moschata variety. 4″ wide by 6″ long fruit.
- Tromboncino: 70 days. Unusual Italian summer squash with a long, crooked neck and a bulbous base. Can reach 3 feet long!
Planting Summer Squash
I’ve found volunteer summer squash appearing in the spring in the prior year’s beds. The seeds are packed with lots of vigor and are ready to sprout! Let’s discuss the perfect conditions to inspire healthy plants.
When To Plant Summer Squash
Plant your seeds in the spring after the danger of frost has ended. The soil temperature needs to be 60 degrees or warmer for germination. 70-95 degrees is considered optimal.
You can start your plants 2-4 weeks before the final frost indoors if you’d like. This allows you to use a seedling warming mat to maintain the perfect soil temperature. Once your seedlings are at least 3 weeks old, you can begin to harden them off to the outdoor climate if it’s warm enough.
If squash bugs are a problem in your area, they’re most active in the spring months. You can avoid them entirely by waiting to plant your summer squash until the late spring or early summer. Once the weather begins to warm up, they’ll disappear.
Summer squash can continue to be sown throughout the summer months if you want more plants. Stop sowing seeds about 12 weeks prior to the first expected frost date, though. Your plants may hold up to early frosts and produce a late-season crop, but won’t survive the winter.
Summer squash is a sun-worshipping plant. An area with full sun is absolutely ideal for your plants! While they may still survive in partial shade, they won’t be as prolific in producing fruit.
Be sure the area you select has good airflow, as well. Any area which doesn’t get a good breeze can be risky, as summer squash are susceptible to mildew. Space your plants out to provide plenty of surrounding airflow.
Raised beds and containers do work well for growing summer squash, but be mindful of the plant’s size. Many varieties can spread to reach 2-4 feet in width. You’ll need larger containers than you’d expect, and they can quickly take over a raised bed!
To guarantee you have sturdy root development, plant seeds about 1″ deep. Summer squash seeds will germinate even if they’re shallow. However, the resulting plant may not form as deep of a root system, and may be less productive as a result.
Making hills or mounds for your squash to grow on is a popular technique. The plant sits at the top of the hill, and the sloped surface allows lots of space for growing fruit. You can grow your summer squash on a flat surface as well, but it may be more difficult to harvest produce.
If you plan on saving seeds, avoid having multiple types of summer squash. Cucurbita pepo will easily cross-pollinate. The seeds of cross-pollinated fruit can become hybridized. Instead of having the green zucchini you’re expecting, you may end up with a yellow zucchini! But if you’re just growing them to eat and not planning on saving seeds, this isn’t a problem.
Growing Summer Squash
I’ve had summer squash literally grow themselves. Needless to say, it can be one of the easiest vegetables to grow! But let’s discuss the best conditions you can offer to ensure a bountiful harvest.
Sun and Temperature
Don’t skimp on the sunlight! Summer squash plants love full sun conditions. Their broad leaves will provide the needed shade for their fruit. Be cautious if you prune them, because the fruit does need protection to avoid sun-scald.
Green, white, and yellow zucchini, yellow squash, pattypan, and all the rest will handle the heat. Be sure to provide extra water during the hottest months of the year. When the weather shifts to cooler climates, start keeping a watchful eye on them. Most summer squash dislike temperatures below 40 degrees Fahrenheit.
Water and Humidity
A good general rule for watering summer squash is to aim for an inch of water per week. This is true of most vegetables, but summer squash can be a bit trickier.
Before watering, check the soil at the base of the plant. If there’s moisture about 4″ below the soil surface, you can stall a little longer. If it seems a little dry, go ahead and water.
Not only do you have to keep an eye on the amount of water, but you also should be careful with how you water. Squash in general tends to be very susceptible to various forms of mildew. Powdery mildew is extremely common, downy mildew a little less so.
To prevent these mildews, I recommend watering only at the base of the plant. Keep the leaves dry. A soaker hose or other drip system which keeps the water at soil level is ideal for this. If your plants have enough airflow and dry leaves, they’ll stay healthy longer.
Humidity can also create moisture buildup on the leaves. While your squash can handle the humidity, stay watchful for signs of mildew.
Fertile soil is required for these plants as they are heavy feeders. Start with well-draining soil or a high-quality vegetable potting mix. Blend in lots of well-aged compost prior to planting to boost the fertility, too.
Looser, well-aerated soils seem to be best for most squash plants. While they can handle some compacted soils, hard-packed clay is too tough for their roots. These plants put down one deep taproot and a bunch of smaller tendril roots. If their taproot can’t easily penetrate the soil, there’s a problem.
Sandier soils will work quite well, as long as you’ve worked in an ample supply of compost. The compost will retain moisture and nutrients your plants need.
5.8-6.8 is the pH range you should aim at, with a perfect zone between 6.0 and 6.5. Check your soil pH before planting to ensure it’s in the right range, and amend if you need to.
Fertilizing Summer Squash
It’s essential to work lots of compost and organic material into your soil. As I said above, summer squash are heavy feeders! Fertilizing your plants is going to be a necessity as well.
Too much nitrogen will cause a lot of green, leafy growth and less fruiting. A monthly feeding of a 5-10-10 fertilizer once the plant’s established is good. If you can’t find a 5-10-10, use a balanced fertilizer.
Compost tea fan? I am, too. A healthy application of compost tea below the plant every 2 weeks will work in lieu of other fertilizer. You don’t have to do a foliar spray with it unless you’d like to. If you do opt to spray the foliage, do it early in the morning to provide time for it to dry fully.
Summer Squash Propagation
Since summer squash is an annual, seed’s the only option for propagation. Extremely easy to germinate at soil temps between 70-95, they’ll still germinate up to 105!
If you are only growing one Cucurbita pepo variety, you can harvest seeds. Allow a couple plants to remain on the vine at the end of the season until they begin to yellow. If they’re a yellow variety, wait until you can’t nick the skin with a fingernail and they’re large. You can then cut the fruit open and easily remove the seeds.
Unlike tomatoes or cucumbers, summer squash do not have a gel that surrounds the seed. Simply rinse your seeds off, removing any clinging bits of flesh, and spread to dry. Once your seeds are dried out, you can store them. Drying can take a week to two weeks in a cool, dark, and dry environment.
Summer squash seeds remain viable for up to six years. The older the seed, the more unlikely it is to germinate, so I don’t recommend keeping them for more than that.
Plants which were started in a bed can be tricky to transplant. Those in pots are much easier.
Potted summer squash can be removed from their existing pot, soil and all. Gently loosen the soil at the base, being careful not to damage the roots. Then place at the same depth it was planted before in its new pot or bed.
If you’re transplanting a summer squash from a bed, you’ll need to be careful. These plants put down one thicker taproot and many finer roots. Loosen the soil at the base of the plant carefully to avoid damaging the root system. Then, use a shovel to lift the entire plant and its soil and roots out of the existing location. Move to its new placement and plant at its original depth.
In both cases, give your plant a good watering at its base once the transplant has been completed. This helps the soil to settle around the plant and ensures the roots have the moisture they need to grow.
Pruning Summer Squash
Pruning summer squash is a point of contention. I often hear people advising not to prune the vines as it allows disease to take hold.
In my experience, this is not universally the case. Yes, any exposed opening to the inner tissues of the plant can allow diseases to spread. However, removing already-diseased leaves can allow the rest of the plant to thrive.
Be selective about how and when to prune. It’s best to prune if you have dense foliage growth to thin out the plant and allow airflow. If there are leaves with signs of powdery or downy mildew, remove the leaf and its attached stem near the vine.
Light pruning encourages the plant to focus on fruit production instead of foliage. It can protect the main vine from disease spread, and can be extremely good for the health of your plant. But be sure to use sharp, clean pruning shears when trimming. Sterilize between cuts to eliminate any fungal spores on the shears.
Both male and female flowers grow on your summer squash plants. You can remove excess male flowers to encourage more fruit development. Look at the base of the flower where it joins the stem to identify which it is. A female flower will have a much larger base, as that’s where the fruit will form. Be sure to leave some male blossoms to allow for pollination!
Harvesting and Storing Summer Squash
Harvesting mountains of crooknecks and pattypans couldn’t be easier. Just snip it and it’s ready to eat! But storage is a bit more complex, especially as these are heavy producers. Read on for some ways of making the most out of your squash supply.
Harvesting Summer Squash
Summer squash is best if harvested young. Longer squash varieties should be picked at 6-8″ in length. You can let them grow to 10-12″ if you plan on stuffing and baking them. Rounder varieties should be harvested at 3-6″ in diameter.
Check your plants every other day once they start to produce. They grow much faster than you’d expect!
You’re welcome to harvest your squash earlier if you’d like! Pattypan squash makes an excellent baby squash variety, and can be cooked whole. These are perfect bite-sized morsels as a vegetable side.
The older you allow your summer squash to get, the less viable it becomes. Large squash has a large seed chamber with mature seeds in it, and much less flesh to eat. The outer skin becomes a bit tougher as well. If it’s tough enough that your fingernail can’t score the skin, it’s probably getting too old to eat.
When harvesting, use a knife or sharp pruning shears to cut through the stem. Make your cut about an inch away from the squash if possible. Some squash varieties can also be twisted off the vine, but this can damage the vine. It’s better to cut them free.
If your squash looks clean, dust off any clinging soil and store it as it is. Squash that have dust or dirt on them can be lightly rinsed off. Allow it to completely dry on the surface before storing.
Don’t forget, the squash blossoms themselves are incredible when stuffed with cheese and cooked. If you have extra male flowers, harvest them and use them right away!
Storing Summer Squash
Baby squash or smaller ones can be stored inside the refrigerator. Place them in a perforated bag, but be sure there’s enough airflow to ensure they stay dry. If necessary, you can tuck some paper towels in to absorb excess moisture, but be sure to check them. If the towel gets too damp, remove and replace it. Once they’re in their bag, they can be tucked into the crisper drawer in your refrigerator for up to 4 days.
Store summer squash that’s larger at room temperature as long as it’s cool. Aim for 60-70 degree temperatures. These will last in a dry, cool place for up to a week, but are best used within a few days time. I’ve had particularly large summer squash last on the counter for up to 2 weeks, but they start to lose their flavor.
If any of your summer squash is becoming discolored or is developing soft spots, throw it out. As a general rule, if it’s a week or less since harvest, you can store summer squash just fine. But it’s better not to risk it if there’s any signs of spoilage.
There’s multiple different techniques you can use to prolong the life of your harvest. These methods work well for squash you plan to cook, but are less effective for use in salads or other raw uses.
Freezing is a popular method. If you plan on using your squash within six months, it’s a very simple process. Wash and dry the exterior of the squash, and cut it into 1/4″ thick slices. Place these into a zip-top freezer bag and remove as much air as possible. Once labelled with the date and contents, you can freeze it for no longer than six months.
Shredded zucchini for use in breads can also be stored like this. Once you’ve shredded the zucchini, sprinkle it liberally with salt and place it in a colander. Leave it on the counter for an hour to allow extra juice to seep out of the squash. Rinse out the squash in a strainer to remove the salt, then place it in a kitchen towel or cheesecloth. Wring out any excess moisture in the squash. You can then freeze the resulting zucchini and thaw it right before use.
If you want to store your zucchini for longer than six months, you can blanch the zucchini prior to freezing. This does make it more bland, so I try to avoid doing so if possible.
Dehydrating summer squash is effective, as is freeze-drying it. Both ways extract all the excess moisture, leaving you with a crunchy disc of squash. The thinner you slice your squash, the more like a potato chip it will become.
Using a pressure canner to store away summer squash for longer periods of time is another option. You’ll need to find a good, food-safe recipe to do this, as summer squash is a low-acid food. You can also opt for pickling methods. Summer squash chutneys or relishes can be incredibly tasty!
Troubleshooting Summer Squash Issues
Summer squash practically grows itself. But there are a few conditions we have to monitor for. Pests are an everpresent plague, some diseases may appear. Let’s discuss the best ways to remedy these problems when they show up.
One of the biggest problems that summer squash growers face is poor pollination. If you don’t have many pollinating insects, you may need to pull out a fine tipped paintbrush and pretend to be a bee.
To self-pollinate your plants, first you’ll need to identify male and female flowers. Female flowers have a bulbous mass at the back of the flower’s base. It’s this mass which will eventually become the fruit. Male flowers lack that ovary. Once you’ve found both male and female flowers, dip your paintbrush into the male flower to pick up pollen. Brush the pollen into the female flower, and repeat as necessary.
Do you have lots of leaves but no flowers? Chances are that your soil has too much nitrogen in it. Nitrogen is great to fuel plant expansion, but doesn’t help at all with flowering. Add something which is potassium-rich to kickstart flower development.
Blossom end rot may be more common on tomatoes, but it appears in squash too. This begins with what looks like a bruise on the end of a young fruit. The forming squash will yellow and rot, eventually falling off the plant.
Usually blossom end rot is a sign of calcium deficiency. I like to work bone meal into my soil before planting to give it a calcium boost. If you’re lacking bone meal or eggshells, tuck a calcium carbonate tablet (like Tums) into the soil. As it dissolves, it releases a quick supply of calcium to the plant.
A wide selection of pests may plague your summer squash beds. Let’s go over how to get rid of these invading insects before they can do severe damage.
One of the most prevalent pests are the tiny black bugs called aphids. These may be green or brown as well, and there’s hundreds of varieties. Aphids spread plant viruses and will also suck the sap out of your plants, causing direct damage. Spray a thin coating of neem oil on all plant surfaces to make them less appealing.
If you’re starting to see red and black bugs in the spring, you may be in trouble. Those may be squash vine borer adults. The squash vine borer lays its eggs on the stems of your vines, and the larvae will tunnel inside. Once inside, they’re hard to fight as they eat your plant tissues, so prevention is key. Floating row covers can help prevent the adults from laying eggs on your plants.
Yellowing leaves, wilting vines? Look for flat, brown-black bugs in and around your plants. If you find some, those are likely squash bugs. These shield-shaped flat squash bugs attack all the Cucurbitae family, and they’re disease vectors. Dusting with diatomaceous earth can keep these pests at bay.
Striped cucumber beetles aren’t just predators on cucumber plants. They’ll happily devour your squash leaves too. Their young will burrow down and chew on the roots, leaving them open to fungal disease. Use a pyrethrin spray to put down these pests before they can multiply.
Creeping pests like snails and slugs are attracted to your juicy squash plants as well. These may hide beneath the shelter of the leaves during the daytime. They’ll then nibble your plants into oblivion all night long. Use a quality snail and slug bait to lure them away from your plants and kill them off.
White, dusty-looking leaves are one of the signs of powdery mildew. This fungal disease thrives in moist environments. For prevention, avoid wetting the leaves, or water early in the morning so the leaves can fully dry. Lots of airflow between plants helps prevent it as well, and neem oil will cure light cases.
Another common issue is downy mildew, also called downy mildew. Humidity is the problem here as well, so prevention is just like treating powdery mildew. If it develops on your plant despite your best efforts, use a copper-based fungicide.
Sooty mold may also appear, especially if you have heavy aphid populations. This is actually a dark-colored mold that forms on the honeydew secretions of aphids. The mold itself won’t harm the plant directly, but it can block sunlight from reaching the leaves. Wipe off any visible sooty mold and reduce pest populations.
Flowers drooping and falling off, or developing a whitish mold? You’ve got squash blossom blight, a common fungal disease on cucurbits. This usually develops during periods of warm, humid weather and can go away on its own. Liquid copper fungicides will help here as well.
Cucurbit bacterial wilt will cause pale and wilted sections of leaves. This can progress into complete plant wilting and death. It’s a bacterial infection spread by cucumber beetles. Particularly nasty on squash, prevention is your best bet. Using a kaolin clay powder to dust your plant with, will help repel pests. Killing off the cucumber beetles is essential!
Finally, the cucumber mosaic virus is non-curable, and is often spread by pests as well. This viral infection will cause mottling on the leaves of your plants. Leaves may become crinkled, as well, and the plant may be stunted in growth. As there’s no cure, your best bet is prevention, and the only way to prevent this disease is to prevent pests. Aphids are usually the transmitting culprit here.
Frequently Asked Questions
Q: Is there really a National Sneak Zucchini Onto Your Neighbor’s Porch Day?
A: Of course there is! After a summer of having fritters, quiche, bread, relish, and of course fresh zucchini, it can be too much. A Pennsylvania resident chose the wee morning hours of August 8th as the date to share the wealth. Lay your green, white, or yellow zucchini on your neighbor’s porch or donate your harvest to a local food bank.
Q: Is yellow squash and summer squash the same thing?
A: While many yellow squashes are summer squash, there are plenty of summer squash varieties that aren’t yellow. Yellow zucchini is one of the more interesting yellow types.
Q: What is the difference between squash and summer squash?
A: Along with different harvest times, summer squash is often much more tender-skinned than winter squash.
Q: Is summer squash the same as butternut squash?
A: No. Butternut squash is a winter squash.
Q: Is it OK to eat summer squash raw?
A: As long as it’s fresh and new, rather than woody, you can eat a summer squash raw.
Q: Which squash is most tasty?
A: We at Epic Gardening simply can’t decide! But scallop and zucchini squashes are great.
Q: Do you peel summer squash before cooking?
A: It’s not recommended. Summer squash cooks very quickly, and removing the skin can make it turn to mush during the cooking process.
Q: Is summer squash a Superfood?
A: All squash is considered a super food, packing in vitamins and nutrients into a healthy carbohydrate source.