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Sunday, January 31, 2016

How & When To Pot Seedlings

In my last post, I discussed seed starting.  Once the seeds have germinated, the next step is to re-pot them so that the plants can continue to grow well before you place them in the garden in spring.

The time to re-pot a seedling is when it has grown its first set of true leaves and when its roots have filled most of the cell in the seed starting flat.

Cotyledons vs. True Leaves: Image from:
The first leaves that a plant produces are called cotyledons.  These are usually 2 smooth, oval-shaped leaves that are the first to appear after the seed germinates.  You do not need to re-pot the seedling when you see these.  Instead, wait for the true leaves to appear.  These are the 3rd and 4th leaves that appear after the seedling has grown for several weeks.  These leaves look like the mature plant's leaves, only smaller (because they haven't grown to full size yet.) See diagram above.

To re-pot the plant follow these simple steps:

1. Fill a small pot of diameter 2-4 inches with a 50/50 mix of well-rotted compost (not manure!) and perlite or a good light potting soil. Try not to use plain dirt from your back yard unless you have to.  This is because the soil from your back yard may contain organisms that can damage the young seedling and/or may not contain enough nutrition for the young plant. If you make your own compost,  it is ok to use that mixed 50/50 with perlite or sharp sand.

2. Water the soil so that it is about as wet as a wrung out sponge.

3. Use a pencil or stick to make a hole in the center of the pot that leaves enough space for the root system of the seedling.

4. Hold the seedling by one cotyledon (baby leaf), and use the pencil to loosen the roots from the tray that the seedling was started in.  Be careful not to tear the stem or true leaves.  Be as careful as you can to avoid damaging the roots as well.

5.  Place the roots of the plant into the hole in the new pot.

Special Cases:  
With most plants, you should only place the roots beneath the soil surface, leaving the stem and leaves clear of the soil. This is to avoid rot.  A few plants are exceptions to this rule.  For example, tomatoes and peppers may be buried more deeply.  For these plants, it is a good idea to
bury the roots AND the stem of the plant up to the level of the cotyledons.  This is because the stems of these vegetables are able to grow more roots.  Burying them deeply at this stage will actually help the plant to produce a stronger root system as well as stronger stem.

6. Remember to label your plants! 

 7. Place the newly potted plants in a bright (preferably South-facing) window.  This time of year, in the north, it is a good idea to continue using a grow light since the days are still very short and since most windows do not let in enough light. Continue using your grow light until the spring equinox (when there are at least 12 hours of sunlight a day.)  or until you place the plant in your garden.

8. Water the plant when the soil feels dry when you stick your finger into the pot up to your first knuckle.  Do not leave the plant sitting in a dish of water. Do not over-water.  This can cause root rot. Most plants fail indoors because the gardener "loves them to death." That is, they get over-watered and/or over-fertilized.  At the same time, you shouldn't under water either. Do not wait until the plant has wilted to water it. Check the soil!

9. If you have used good quality compost and/or potting soil, you should not need to fertilize the plant between now and when the plant is placed in the garden in April or May (in Michigan).  Most compost and potting mixes will contain many months worth of nutrition for a typical plant.

10. If you want a plant to be bushy or to have multiple branches (e.g. peppers, basil, most other herbs etc.), wait until the plant has produced around 6 true leaves and pinch or cut off the tip of the plant below the top two leaves at the level of the stem.  This will cause the plant to branch at this level. With some plants you may continue to pinch or even prune the plant periodically so that it will continue to bush.  Herbs especially benefit from this treatment. See image below:
When & where to pinch.  Image from:

11.  Be patient and RTFSP!  That's right! "Read The ____ Seed Packet!"  The seed packet when it is the best time to put the plant out in to the garden, how far apart to space the plants & etc.  Wait for spring and the last frost.  Wait for it..... waaaaaait.....

Friday, January 22, 2016

"RTFSP" & 14 Other Seed Starting Tips

It's that time of year again: SEED STARTING TIME!

I love seed starting time because it reminds me that although the days are still short, and the snow is still on the ground, spring is coming.  It's such a miracle that a tiny thing like a seed can grow into a beautiful, productive plant in one season!

Here are some of my seed starting tips.  I hope you find them useful.

1. RTFSP!!!!!  You've heard of "RTFM" ("read the freakin' manual"), right?  Well this is "Read the freakin' seed packet!!" Seed packets generally provide most if not all of the information that you need to start any given seed. This includes: when to plant the seed, how deep to plant the seed, whether to start indoors or outdoors, etc.  For the few seed packets that do not have directions, you can always google the type of seed and find directions on how to plant it on the internet. You can also use the nifty app that I found created by the folks at Mother Earth Magazine to figure out when to plant: When to Plant App.  This information is vital!  Do not ignore it!

2. Know your growing zone and last frost date.  Most seed packets will recommend when to plant based on what zone you are in. They also instruct you as to when to plant seed outdoors or set the seedling out based on whether the danger of frost is past or not. Therefore, you need to know your USDA zone and last frost date.  If you don't know these, click here: USDA zone and Frost Dates.

3. Fresh seeds germinate better.  If you have some seed packets that have been laying around for 2-3 years, by all means, go ahead and try to plant them. Just be aware that fewer of these seeds (or possibly none) will germinate. Most seeds expire entirely by year 4-5.  Fresh seeds harvested during the last growing season are more likely to germinate well.

4. Do not spread seeds to thickly.  Try to spread the seeds evenly and so there are a centimeter or two of space between them. This will allow enough space for the seedlings to grow and will reduce the number that you need to dispose of later when you thin them out.

This can be difficult with small seeds because they are difficult to see.  There are several ways to alleviate this problem:
    i. Place the seeds in a salt shaker, then sprinkle them over the surface the soil.
    ii. Mix the seeds in with a small amount of sand so that you can see where you are spreading the seed over the soil more easily.
   iii. Place the seeds into the fold of a creased piece of paper and use a pencil or chopstick to push them off the edge of the paper and into the growing medium one or two at a time.

5. Use a grow light. The photo below was taken at 7am on January 21 in zone 5b, Michigan. As you can see from the window, it is still dark out. Most flower & vegetable seedlings need around 12 hours of direct light to grow well.
7am in Brighton, Michigan - Still Dark Outside

If you live in the North, even your brightest window cannot provide enough light in the winter.  The days are simply too short. You can still try to plant the seedlings without a grow light, but they are likely to be "leggy," i.e. tall, scrawny and weak.  If you must start seeds without a light, use a South facing, bright window, and I wouldn't even bother starting them until at least March in order to have a chance for the plants to get enough sun.

Grow lights range widely in price. You can get full spectrum light bulbs from a big box store that may only cost you a couple of bucks and can be plugged in to a clamp lamp that may only cost you around $10.  You can purchase a stand with a light like I show in the picture for around $50.  There are several DIY you tube clips that show how to build your own stand from PVC pipe that may cost you around $30 or so to make -- less if you already have scrap PVC available.  So, please do not be deterred if you Google "grow light" and find units that cost a couple hundred dollars. You don't need those for vegetable seedlings... those are more for growing plants of either a tropical or illegal nature.

6.  Use seed starting medium.  Seeds may start in regular potting soil or soil from your garden, but generally they don't root well have a higher risk "dampening off" or rotting.  Seed starting medium drains better and allows for better root production. As plants become larger, you can transplant them into larger pots containing a more nutrient-dense potting soil.

You can buy ready-made seed starting mix at any big box store.  According to the American Horticultural Society Plant Propagation book, you can also mix your own by combining: "3 parts peat, 1 part fine bark, 1 part perlite.  To each 8 gallons (36L) add 1 1/4 oz (36g) of slow-release fertilizer and 1 1/4oz (36g) of dolomitic limestone."

7. Water gently.  If you run your seeds under a tap or water them with a standard watering can, you are likely to wash the seeds away.  Instead, soak your seed starting mix ahead of time so that is damp like a wrung out sponge and plant into that without watering after.

When the seed mix dries out with time, water it with either a spray bottle or make your own gentle watering can by hammering some holes into the lid of an old plastic bottle using a pin or needle. (Do not use a nail, that will make holes that are too large.)  You simply squeeze the water-filled bottle gently to create a fine spray of water for the seedlings.  Easy!

Be careful not to over water.  Although seeds need to be kept slightly damp to germinate, over-watering can lead to mold growth and/or dampening off (seedling death).  The planting medium should never be wetter than a wrung out sponge. 

8. Temperature matters. Most common vegetable seeds will germinate between 65-75F or at room temperature.  A few will need cooler or warmer temperature. Some even need to be left in your freezer for a number of weeks before they will germinate. RTFSP!! Your seed packet will tell you what temperature the seeds need to germinate!

If your house is too cool for the seeds to germinate, you can buy a seed heating mat.  These can be found on or at various seed companies.  I personally do not use these as they are expensive. Instead, I purchased a personal heating pad at my local drug store (the kind you use when you have a sore back).  These have the disadvantage of being shorter than most seed trays. But they tend to be less expensive and also have a safety feature where they turn off automatically if they get too hot.  This helps relieve my concern over potentially burning the house down. Both options are relatively water proof (but do not submerge them in water - danger danger!!)

9. Label your plants. I know, you have a great memory, right? Believe me, you'll forget which pepper was which by the time May rolls around. So label your plants! I suggest using popsicle sticks as labels. They are cheap, you can buy 500 at a time, and you can compost them when you are finished with them. 

10. Pet your plants.  When your seedlings emerge, remember to pet or tickle them. This is not only fun, but imitates the wind and helps the stems to toughen up. Alternately, you can run a small fan next to them, but that uses more electricity and isn't as fun!

 11. Be patient.  Some seeds take only a few days to sprout.  Some take weeks. Others, a few months. (See tip #1 above.)

12. Only plant what you like.  There is no point in planting beets if you hate the flavor of them.  There is no point planting marigolds if you hate the color orange.  Most of us have either limited space to grow, and/or limited time in which to care for plants.  Use your time and space wisely by growing only the plants that you will use and/or love. 

13. Try a new seed type (or several) every year. There are so many types and varieties of plants out there, and seeds are inexpensive. It is fun to try new varieties to see how well they grow for you, how they taste, or how they differ in appearance. Go for it!

14. Do not fret if seeds or plants do not grow.  Again, seeds are cheap.  If you buy a potted plant at the nursery and it dies, you are out $10-$200.  But even if every seed in a packet dies, you are only out $0.30- $5.00.  So no worries there. Also, plants vary in their climate needs, the freshness of seed, water requirements etc.  If they don't grow, it may have nothing to do with you or your skill.  They just may not like your window, or your climate. So do not decide that you have a "black thumb" based on one packet of seed or even several! Keep trying. Keep learning to improve your growing knowledge.  Some plants will grow. Some will die.  Most will grow. They "want" to live every bit as much as you do!

15. HAVE FUN! :) 
Later in the season, I will post a bit more about prepping your seedling for planting in the garden.  This includes: re-potting the seedlings into larger pots, hardening them off and planting them out. So please keep reading the blog!



Note: I make no claims as to whether one company is better than another.  These are simply the companies where I found my seed this year. 

Terroir Seeds
Ferry-Morse (sold at most big-box stores)
Burpee (sold at most big-box stores)
Dollar Seed
Hart Seed Company (sold at most big-box stores)
Nichols Garden Nursery 
Botanical Interests 

2 Bonus Tips: Organize your seeds by the month you wish to plant them in an old shoebox.  Use note cards to separate them by month. Throw a pencil and some popsicle sticks in the box too so that you remember to label your seeds.


For those of you who really want to nerd-out, or who need a new idea, here is a list of what I am growing this year and when I plan to start the seed for you to read:


Hot peppers: Ancho, Hungarian Sweet, Anaheim, Jalapeno, Orange Scotch, Cayenne

Alliums: American Flag Leeks, Garlic Chives, Common Chives, Golden Grande Onion, Red Burgundy Onion, Sweet Spanish Onion

Flowers: Coconut Geranium, Cherry Pie Heliotrope


Herbs: Costmary, Lime Balm, Fennel

Tomatoes: Box Car Willie, Ace 55, Yellow Plum, Great White, Beefsteak, Roma, Small Red Cherry

Flowers: Evening-Scented Stock, Pot Marigolds, Sweet Peas, Lobelia 'crystal palace', Blue Pimpernel,

Celeric Giant Prague

Vegetables: Pepper Sweet California Wonder, Victoria Rhubarb


Eggplants: Black Beauty, Burpee's Garden Blend

Flowers: Cosmidium Brunete (Chocolate Cosmos), Forget Me Not, Chicory

Herbs: Summer Savory, Winter Savory, Parsley, Cinnamon Basil, Sweet Basil, Fenugreek, Caraway

Brassicas: Kale Blue Vates Scotch, Cauliflower Early Snowball, Broccoli Waltham 29


Flowers: Nasturtiums, Larkspur, Lewis Flax, Flanders Poppy, Columbine Rocky Mountain Blue, Showy Milkweed

Greens: Green Cabbage, Taipai Red Cabbage, Red Acre Cabbage, Corn Mache

Herbs: Chinese Celery, Borage

Root Vegetables: Parsley Hamburg or Turnip Rooted, Rutabaga American Purple Top Yellow, Carrot Danvers 126, Carrot Burpee Kaleidoscope Blend, Seven Top Turnip


Herbs: Common Comfrey, Anise

Flowers: Love in a Mist

Vegetables: Peas Alaska,  Endive Green Curled Ruffec

AFTER MAY 16 (last frost) OUTDOORS

 Flowers: Bachelor Button Blue Boy, Morning Glory Heavenly Blue, Wild Flax Saphyr, Sunflower Italian White, Lupoine Texas Bluebonnet

Greens: Shiso Red, Spinach New Zealand, Swiss Chard Bright Lights, Lettuce Giant Caesar, Lettuce Crisphead Great Lakes

Vegetables: Radish Cherry Belle, Bush Bean Golden Wax

Squash: Acorn, Spaghetti, Buttercup, Butternut, Pumpkin Early Sugar Pie


Grains: Sweet Corn Trinity Hybrid, Sweet Corn Silver Queen

Vegetables: Bush Bean Goldrush, Cucumber Lemon, Cucumber Marketmore, Okra Burgandy,

Squash: Zucchini Black Beauty,  Cocozelle, Yellow Early Prolific Straight Neck, Luffa

Watermelon: Crimson Sweet, Sugar Baby

Herbs: Dill Fern Leaf


Hard Neck Garlic

Wild Leeks

Common Chives

Note: I will likely do another planting in mid-summer and/or inter-plant crops throughout the summer. I will try to post about these plants as I grow them.

Sunday, January 10, 2016

Winter Gardening in Michigan Experiment & 38 Vegetables to Grow in a Zone 5 Winter

This winter, I decided to try growing food outdoors in a cold frame for the first time.  I was inspired to do this by the gardening shows, books and you-tube videos that I've been viewing lately. These included: Elliot Coleman, Alberta Urban Garden, Gardener's World, and One Yard Revolution, among others. Based on watching these folks talk about their gardening experiences, I developed the following...



 If vegetables can be grown in the middle of freakin' Alberta in the middle of the winter, surely I can grow them here in southern Michigan! (Granted, I've never been to Alberta, but I have been to Quebec, and I can safely say that Canadian winters are no joke: they are coooold!  If the plants can deal with that climate, they should be able to deal with this one, right?)



Store-bought cold frame
 I set up 2 cold frames. One, I bought on Amazon. The other, I made out of an old window that my neighbor was throwing out set on top of some bags of peat and wood mulch that I plan to use next spring.  I just arranged the bags of mulch etc. in a rectangle, and set the window on top. Anywhere there were gaps, I covered the area with some small garbage bags filled with compost. It looks kind of trashy, but works.

Home-made cold frame
In mid-September, I planted the seeds for the following: spinach, chard, cilantro, lettuce, radishes, arugula, and carrot. I chose these
plants because they are known to be cold tolerant. (See the bottom of this post for a more complete list of cold-tolerant crops.)  I also put some of my rooted cuttings into the cold frame to protect them through the winter.

In November, I set up some PVC pipe hoop houses over the top of the cold frames.

To cover my home made cold frame I hammered some 2 foot long rebar into the ground.  I cut a 1" diameter PVC pipe into lengths of about 5 foot and arched them over the top of the home-made cold frame, securing the ends by inserting the rebar into the center of the PVC pipe.  I braced the two arches with a 3rd piece of stiff PVC pipe at the top of the arc. I secured the pieces together with zip ties. I then covered the hoop tunnel with 6mil plastic sheeting and
clamped it to the PVC pipe with plastic clamps found at the big box store. I anchored the plastic at the bottom with rocks and bricks.

To cover my store-bought cold frame, I cut a 1" diameter PVC pipe into four, 4 foot pieces, and one 5 foot piece. I connected them at the top with a 3-way PVC pipe connector. Unfortunately, one of the 3 holes for the connector contained a segment that was too small for the top piece of PVC pipe, so I connected that again with pieces of zip-tie. I secured the ends to the ground by inserting the rebar into the center of the PVC pipe. I covered this with 6mil plastic and secured it with plastic clamps from the big box store.  I anchored the plastic at the bottom with rocks and bricks.

(See, not so scientific. I didn't keep track of what type of seed, how much I planted, when it germinated or anything really.  My former biology professors would weep with disappointment. ;) ) 


Several of my vegetables grew and I was able to harvest several winter salads. But, my method needs tweaking.

What Worked:

Spinach, chard, cilantro, lettuce, radishes, and arugula all grew.  The cuttings in their 4-inch pots seem well protected (these included sweet woodruff, rosemary, and gooseberries).  The radishes grew quickly and were harvested before the end of October. The lettuce also grew quickly until October, but then slowed down by December. Even so, I got 2-3 cuttings out of it, including one for Thanksgiving salad. The cilantro and spinach were the BEST. I can never get these two vegetables to grow without bolting in the summer. But in the winter under the cold frame (September - January) they have produced wonderfully and are sweeter tasting than usual! I cut the cilantro about 4 times, and the spinach about 3 times.

What Failed:

There was not quite enough plastic to cover the PVC tunnels.  When it got windy, the plastic would lift up along the bottom of the tunnels, despite the anchoring with rocks and bricks.

Some of the carrots germinated in the home-made cold frame, but did not continue growing past late October.  I think this is for two reasons:

1. I planted them too late. According to the chart in  Elliot Coleman's book, "The Winter Harvest Handbook", I should have started the carrots around early to mid August. Then, theoretically, they would have been ready for harvest around mid to late December.

2. I positioned the home-made cold frame facing East instead of South. I did this for easy access, but it may have decreased the amount of light getting to the carrots.

The arugula grew well in the store-bought cold frame through mid-November, but by mid-December they were frost burned and mushy.  I think this was because they were planted near the edge of the North-end of the cold frame, and thus got hit with frost.  This is somewhat surprising because it has been a rather mild winter for Michigan. We did get a couple of snows, but nothing outrageous. This has caused me to consider what might need tweaking...


I am going to try growing winter carrots again, but next year I will start the seed in August. Hopefully I will have carrots for Christmas 2016.

I will be buying a larger piece of plastic to cover the hoops next year.  I want enough plastic left at the bottom that I can either bury some of it or anchor it more securely with bricks. I don't want the edges kicking up in the wind and releasing the built-up solar heat. 

I am going to use some left-over trex decking boards to build a proper cold frame for the window that I pilfered from the neighbor's trash.  Although the bags of peat insulate well, they look pretty ugly, and I don't plan on buying peat every year. If I have a trex frame I can move it around easily and store it away under the deck in the summer. I will post building instructions for this in the summer after I complete the construction.

 It seems to me that the store bought cold frame needs some insulation despite being double-covered with the plastic tunnel.  (The trex frame may need insulation as well.) This winter has been unusually  mild, with temperatures averaging around 40F - 50F. If we get a true Michigan winter (like the winter of 2013 or 2014), I think that more than just the arugula will suffer.

I am not sure how I will insulate the cold frame next year, but,I have several ideas:

1. I could dig a 1-2 foot deep square, plant the seeds at the bottom of the hole and put the cold frame over that.  My concern with this is that the edges of the hole might crumble and I will end up having to build yet another structure to hold them up.

2. I could fill several milk jugs with water, paint the outside black and line these up along the outer edge of the cold frame to act as heat sinks.  My concern with this that this will take up growing space inside the cold frame. I could line them up between the outside of the cold frame and the plastic hoop structure, but I think this might not hold heat as well.

3. I could pile leaves up between the cold frame and the plastic from the hoop over the top.  My concern with that is it may make a slimy mess on the surface of the cold frame by the time spring gets here.  I could decrease the mess by bagging the leaves in plastic garbage bags, but that is a waste of more plastic.

4. I could get some bubble wrap or styrofoam and line the inside of the cold frame with it. I could re-use that every year.  But would it be thick enough to do the job?

5. I could put some floating row cover over the plants inside the cold frame.  This might help, but I doubt will be enough by itself.  Perhaps if I insulated with styrofoam and applied floating row cover the plants would have enough protection.

If you are reading this and have any better ideas, or ideas that you've tried in the past, please let me know in the comments.  I would appreciate the help!

 I further plan to heat the cold frames next year from below: by building a hot bed.  Hot beds appear to be simple to set up (I have not built one myself yet - another upcoming experiment!) Apparently, you just dig a trench or hole, pack the bottom 12 inches of the hole with fresh horse manure mixed with straw or leaves, and then lay garden soil to a depth of about 5-6inches over the top of that. As the manure decomposes, it will produce a couple degrees of added heat.  I plan to build a hot bed in spring as well in order to assist the watermelon that I want to grow. I will post more about this when I do it.

I will, of course,  post again next winter to let you know what changes I made and how well the crops grew.  For now, I am pretty satisfied with my first attempt.  I got several winter salads and a ton of cilantro out of my little "experiment." I have great hope that I will only improve the process year by year.

BONUS! List of  38 Winter-Hardy Vegetables for Zone 5 Cold Frames:
(i.e. plants that will grow under the protection of an un-heated greenhouse or cold frame in Zone 5 Michigan, according to Eliot Coleman & others.)

If you live outside zone 5, Michigan, please see the chart in  Elliot Coleman's book, "The Winter Harvest Handbook to figure out what you might be able to plant in your zone. 

Arugula - in zone 5, plant between 8/1 and 9/1 to grow in cold frame over winter
Beets - in zone 5, plant between 8/1 and 10/1 to grow in cold frame over winter
Broccoli - in zone 5, plant between 8/1 and 9/1 to grow in cold frame over winter
Brussels sprouts - in zone 5, plant between 8/1 and 9/1 to grow in cold frame over winter
Cabbage - in zone 5, plant between 9/1 and 9/15 to grow in cold frame over winter
Carrot - in zone 5, plant between 8/1 and 9/1 to grow in cold frame over winter
Cauliflower - in zone 5, plant between 8/1 and 9/1 to grow in cold frame over winter
Celery - in zone 5, plant between 7/1 and 8/15 to grow in cold frame over winter
Celeriac - in zone 5, plant between 7/1 and 8/15 to grow in cold frame over winter
Chard/ Swiss Chard - in zone 5, plant between 6/1 and 9/15 to grow in cold frame over winter
Chicory - in zone 5, plant between 7/10 and 8/20 to grow in cold frame over winter
Chinese cabbage / Oriental vegetables - in zone 5, start seeds mid summer to grow in cold frame
Chives - in zone 5, plant between 8/1 and 10/15 to grow in cold frame over winter
Cilantro - in zone 5, start between 9/1 and 10/1 to grow in cold frame over winter
Claytonia - in zone 5, start between 10/1 and 11/1 to grow in cold frame over winter
Cress - in zone 5, start between 9/1 and 10/1 to grow in cold frame over winter
Dandelion - in zone 5, start between 9/1 and 10/15 to grow in cold frame over winter
Endive - in zone 5, start between 8/1 and 9/1 to grow in cold frame over winter
Escarole - in zone 5, start between 8/1 and 9/1 to grow in cold frame over winter
Kale - in zone 5, start between 8/1 and 9/15 to grow in cold frame over winter
Kohlrabi - in zone 5, start between 8/15 and 9/15 to grow in cold frame over winter
Leek - in zone 5, start between 8/1 and 8/15 to grow in cold frame over winter
Lettuce - in zone 5, start between 8/25 and 10/1 to grow in cold frame over winter
Mizuna - in zone 5, start between 8/15 and 11/1 to grow in cold frame over winter
Onion bulb -  in zone 5, start between 9/1 and 10/15 to grow in cold frame over winter
Onion greens - in zone 5, start between 8/1 and 10/15 to grow in cold frame over winter
Parsley - in zone 5, start between 9/1 and 11/15 to grow in cold frame over winter
Parsley root - in zone 5, start between 9/1 and 11/15 to grow in cold frame over winter
Parsnip - in zone 5, start between 8/1 and 9/1 to grow in cold frame over winter
Peas - in zone 5, start between 9/1 and 11/1 to grow in cold frame over winter
Potato - in zone 5, start between 7/25 and 8/20 to grow in cold frame over winter
Peppermint - in zone 5, any time before 9/15 to grow in cold frame over winter
Radish - in zone 5, start between 9/1 and 11/15 to grow in cold frame over winter
Rutabaga - in zone 5, start between 7/15 and 8/15 to grow in cold frame over winter
Sage - in zone 5, any time before 9/15 to grow in cold frame over winter
Sorrel -  in zone 5, start between 8/15 and 10/1 to grow in cold frame over winter
Spinach - in zone 5, start between 9/15 and 11/1 to grow in cold frame over winter
Turnip - in zone 5, start between 9/1 and 10/15 to grow in cold frame over winter

Note: Theoretically, you can also grow things like tomatoes, basil, peppers, cucumbers & melons year round. However, these would require a larger greenhouse due to their size as well as some coddling and extra protection to keep them warm enough.