I am a firm believer that understanding the “why do” behind the “how to” drives us to become better, more confident gardeners. One of the best people I know to explain the science behind great gardening is Dr. Lee Reich, and on this week’s encore episode I am revisiting an insightful conversation we had a few years back on how expanding our scientific knowledge a little can help our gardens a whole lot.
Lee is a repeat guest and great friend of the podcast with so much knowledge to share. He has a Ph.D. in horticulture, a master’s degree in soil science and a bachelor’s in chemistry. In this conversation, we discuss the interesting facts and valuable advice in his book “The Ever Curious Gardener: Using a Little Natural Science for a Much Better Garden.” Lee’s other books include “Weedless Gardening,” “Grow Fruit Naturally” and “Uncommon Fruits for Every Garden,” and he is also a national gardening columnist for the Associated Press.
Lee lives in New Paltz, New York, on his “Farmden” — more than a garden, but less than a farm — and previously worked in plant and soil research for the U.S. Department of Agriculture and Cornell University before shifting gears to writing, lecturing and consulting. For more details on Lee’s insights from this episode, you can read the show notes from the original airing of our conversation.
Why You Should Never Skip Hardening Off
Plants can get sunburned, start to wilt and even die when they are suddenly moved outside and left in the sun. Tender seedlings and houseplants that were coddled indoors need to be gradually introduced to the new environment in a process known as “hardening off.”
In “The Ever Curious Gardener,” Lee explains the physical changes that happen to plants to acclimate them to full sun and wind. He says plants brought outside should initially be left in dappled shade in an area sheltered from too much wind, and should be brought back indoors if the temperature is expected to drop.
Lee prepares plants to be moved outdoors by giving them a brushing. That’s right — he goes over the tops of the plants with a brush once each day. He does this because of thigmotropism, the phenomenon of plants responding to touch. He says this makes the plants stockier and more prepared for outdoor conditions.
To acclimate plants to the sun, I leave them out for just a half-hour in the sun on their first day outdoors. On the second day, I leave them for an hour. By the end of a week or 10 days, I have increased the time to a full eight hours so they are ready for a full day’s worth of unfiltered sunlight. Hardening off takes patience, which sometimes us excited gardeners are short on, but it greatly reduces sunburn.
Seed Stratification and Scarification
You may be familiar with seeds that require stratification before they will germinate. But do you know why they need stratification, or cold treatment, in order to sprout? Lee explains that these seeds contain abscisic acid, a germination inhibitor that helps them survive the winter. Abscisic acid breaks down when exposed to cold temperatures, so it is ready to germinate in spring. Lee says this can be replicated by putting seeds in a bag of moist potting mix or perlite in the refrigerator for a sufficient amount of chilling hours.
Some seeds delay germination with a hard coat that air and moisture can’t get through. To speed up germination, the seed coats can be mechanically scratched or nicked.
The Unseen Life in Soil
Everything in the soil that is or was living — from plant material and dead bugs to bacteria and fungus — is known as soil organic matter. Good soil is approximately 5% organic matter. Though it’s a small portion, that 5% is fundamental to the ability of the other 95% (water, air and minerals) to sustain plants. Organic materials have a negative charge so they bond with positively charged nutrients. As the organic material slowly decomposes, it releases the nutrients into the soil gradually so plant roots can take them up.
Soil organic matter is always breaking down due to microbial activity and the activity of other living things, like worms, adding fertility to soil. In a well-cared-for garden, organic matter is often added in the form of compost and natural mulch.
Why Organic Fertilizer Beats Synthetic Fertilizer
Nutrients in synthetic fertilizer are designed to be immediately taken up by plant roots — what’s left washes away, polluting water bodies. But organic fertilizers release nutrients at a rate that is proportionate to the maturity and needs of plants.
It is possible to be overly generous with organic matter when amending soil, but an abundance of organic fertilizer will not burn plants easily the way that too much synthetic fertilizer does.
Why Garden Soil Doesn’t Belong in Containers
When we have good garden soil we may be tempted to use it in a container instead of buying potting mix. However, this simply doesn’t work out. Garden soil is too dense for a container and will hold water, causing plant roots — which require oxygen — to drown. Adding more drainage holes to the container will not be enough to change this. The capillary attraction in the soil will be too much to leave room for water to pass through and drain out as it should.
An aggregate like perlite or sand added to soil will make it more porous and reduce capillarity. The aggregate should be mixed in evenly — not just added to the bottom of a container. When rocks or another aggregate is placed in the bottom of a pot before adding soil, it does not improve drainage. In fact, quite the opposite happens. Water collects above the aggregate level, rather than collecting at the bottom of the pot near the drainage holes. This essentially reduces the depth of the pot and puts plants at risk of drowning.
I made a video demonstrating how rocks or other bulky material at the bottom of containers does not improve drainage, and in fact, makes it worse. The video really illustrates the point well.
Why to Avoid Tilling
Tilling is a common gardening practice, but I’ve learned that tilling can disturb the beneficial microbial activity and important organic matter in soil. Tilling destroys soil structure, disrupts mycorrhizal fungi networks and introduces oxygen that speeds up the decomposition of organic matter to a much faster rate than it should be for healthy soil and healthy plants.
Lee points out that tilling also uncovers seeds, exposing them to the sun, which stimulates germination for many weed seeds. Instead, Lee likes to layer paper over the existing vegetable, wetting it down and covering it with compost. He plants directly into the compost and finds that the seeds grow roots down through the wet paper into the turf, which itself breaks down and releases nutrients.
I hope you found my conversation with Lee Reich valuable. If you haven’t listened yet, you can hear this episode now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
What scientific questions do you ponder in the garden? Let us know in the comments below.
Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
joegardenerTV YouTube: How to Get the Best Drainage for Your Container – Why What You’ve Been Taught Is All Wrong
joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.
joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.
joegardener Online Gardening Academy Growing Epic Tomatoes: Tomato expert Craig LeHoullier joins me in leading this course on how to grow healthier, productive tomato plants and how to overcome tomato-growing challenges.
“Weedless Gardening” by Lee Reich
“Uncommon Fruits for Every Garden” by Lee Reich
Disclosure: Some product links in this guide are affiliate links, which means we would get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us. None of the items included in this list have any bearing on any compensation being an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, Milorganite, Soil3, Exmark, Greenhouse Megastore, High Mowing Organic Seeds, Territorial Seed Company, Wild Alaskan Seafood Box and TerraThrive. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.