When To Plant And What To Do To Protect Against Frost

From September 2012

have been growing a lot of plants indoors since early February. I have sowed seeds regularly since according to my 2020 Planting schedule – Planting times

The exciting thing about this growing season is the successful implementation of my homemade soil blocks. A Soil block is a block of growing medium that has been lightly compressed and shaped by a form. A soil block serves as both a container and the soil for starting and growing seedlings, eliminating the need for plastic pots and trays for transplanted seedlings. Seedlings grown in soil blocks form stronger root systems than those grown in containers due to increased oxygen to the roots and the soil block’s natural tendency to “prune” roots . Plants suffer less transplant shock because they are put directly into the ground rather than being transferred from pots and having their roots all swirled.

In episodes 48 and 69 I provided videos of how to make soil blocks and what the results were. The success of this experiment was better than expected. Green onions, chives, parsley, endive, swiss chard, basil, asters, marigold, hot peppers, eggplant, tomatoes, okra, 4+clocks, oregano, thyme, chamomile, etc. Were all sown in soil blocks. All except chives and marigold had a 100 percent success rate for sprouting and growing. The marigold may have been bad seeds as the seeds I sowed were the second generation and I wonder if they were bred to not produce seeds.

Integral to when plants get sowed is the date I use for the last spring frost. Frost forms in much the same way as dew forms. Frost usually forms when a surface cools through the loss of infrared radiation to a temperature that is colder than the dewpoint of the air next to the surface, AND the temperature of that surface is below freezing (32 deg F, or 0 deg. C). The source of this moisture is water vapor contained in the air. 

Signs of Damage

As with all plants, if the tomato plants are suffering from frost damage, it will be visible very quickly. Wilting and discoloration are the most visible signs. With a light or very short-lived frost, often only the outer edges of the plant are damaged. These areas can be trimmed off without inflicting further damage on the plant. However, if the ground freezes at all the root system can be damaged and this will kill the plant almost immediately.

Last spring frost is the date after which frost is not likely to occur. The dates I sow plants are dependent on the planting guides that I researched in Mel Bartholomew’s SFG and the date I use for the average last spring frost. . The planting guide is an Excel spreadsheet and can be downloaded. I also have a link in the show notes to Victory Garden’s website which lists the average spring and fall last and first frost dates for all states.

For the past 3 years, I have been using the third Friday in April as the last spring frost date. I must say however that there is no absolute fail-safe date for the last frost. If I wanted to be safe I could use the second Friday in May as the last frost date. However, I’ve never been able to wait that long because the plants I start from seed all grow too big and cannot fit under the grow lights anymore by the third Friday in April.

Planting vegetables and flowers in the ground before the last frost can be devastating especially if the plants were started from seed. All the time, hard work and energy spent would come to naught if attention is not given to the weather. If a frost hits while new young plants like peppers, tomatoes, and cucumbers are in the ground unprotected and temperatures go below 41 degrees Fahrenheit they quickly start a freezing process in the cells of the plant due to their high water content. As the water cells freeze, the cell walls begin to burst, and affected sections quickly discolor, curl and these areas will not regenerate. The cellular breakdown does not spread like a virus or bacteria but the plant wastes a lot of vital energy trying to revive the lost growth.

To ensure the growth and protection of young plants I employ two techniques to give them a better chance. First, I harden the plants and get them used to the outdoors by placing them outside for an hour two each day starting two weeks prior to the intended planting date. This is hard to do but I employ my kids in this activity which makes it much less of a chore for me. The time the plants are left outside should be extended as the days progress. Hardening plants is important because if you suddenly put them outside, to face the rigors of nature with wind removing water from the areas near the leaves, making it drier and forcing them to increase transpiration, their tissues are not adapted to drawing in water from the drier soil, they are not adapted to the outside temperatures and their tissues cannot take the buffeting of the wind. The plants will therefore suffer. Some plants will have stunted growth and others will die without the hardening off period.

The other thing I do to protect young plants is to cover them to ward off frost. Covering them can also be useful to protect against insects that like to munch on the leaves of young plants. I have a lot of frost-hardy plants in the ground already such as peas, chard, spinach, and radish and the slugs are doing their best to munch up what they can. I’ve found covering plants the way I do does not protect them much from slugs. For slug protection, I place plastic covers made from water bottles that I cut open. The slugs can’t get to plants that way and the ones they do get are expendable to begin with. 

But the important thing is frost protection. We had an incredibly warm February, A warm March and April started warmer than usual. However, as is typically just after I planted the tomatoes, Okra, 4 o’clock, sunflowers, basil, etc. last week we got hit with 2 solid days of cold hard rain. I knew the rain was coming which is why I wanted to get the plants in the ground but I didn’t anticipate the cold that accompanied it. Or at least the temperature was not predicted to dip below 40 degrees as it did. I did most of the plantings between April 19 and 21 and the rain started an hour after I was finished. It wasn’t bad on Saturday but I awoke to a cold and blustery Sunday. I knew my work would be wasted if I did not take steps to protect the plants that were most vulnerable. Thus I was outside Sunday in the rain rigging up the PVC pipe and 4 mil clear plastic sheeting.

I got this idea from Mel Bartholomew’s square foot gardening a few years ago and it has always served me well for my purposes. Most people advise against plastic sheeting and prefer cheesecloth. However, I need a lot of this stuff and I’ve yet to find cheesecloth big enough to cover my gardens. The potential heat build that clear plastic can cause is really limited to situations in which the covered area would be small with no heat escape and help magnify the sun’s rays greatly. The way in which I set up the PVC domes leaves plenty of space and openings that diminish burning potential.

For a typical 4foot by 4-foot square garden I would take two 10 foot long ½ inch PVC pipes and bend each end into a corner of the garden in a manner that forms a large hooped X over the garden. I then take each of the plastic to drape over the frame and I use whatever is available to hold the plastic down. It’s pretty simple and the photos at Todolisthome depict one of the gardens I protected last weekend. I covered 5 of the gardens in all and protected other at-risk plants with plastic bottles. 

The weather has turned up a little. We still have some rain but the day temperatures are in the 60s and the evenings are just above 40. On a couple of my hugelkulture beds the rains have brought out the slugs and they have mauled some of the sunflowers and peas. The cold rain and my delay in covering the plants resulted in one lost tomato plant so far and 2 others with slight damage on a leaf or two. In the future, I am going to move my last frost date to two weeks later and make it the first Friday in May.

Right now the best thing for me to is to follow Permaculture Principle Observe and Interact –By taking the time to engage with nature we can design solutions that suit our particular situation.

That’s it for today now go and get ready for fall Gardening.


For a four foot by four-foot garden: 2 – 10 foot ½ inch PVC pipes, bend from corner to opposite corners, secure with a zip tie, cover with 4 mil clear plastic or cheesecloth, secure with bricks or branches.

August 18, 2020

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