Soil temperature and why it matters

soil thermometer in the ground
Soil thermometer. Photo: A. Bodkins

Sunshine, increasing temperatures, warm rain showers, and the return of migratory birds are all signs that Spring is getting closer. They are all reasons to be excited about Spring and all the possibilities that the new gardening season will hold.  

It’s always tempting to go out and start sowing seeds at the first glimpse of sunshine, but most seasoned gardeners know that patience is the best policy. It takes several weeks of warm air temperatures and sunshine for the soil temperature to get warm enough to signal the seeds to germinate. Mother nature provides mechanisms to protect seeds from germinating too early (called “seed dormancy”) and there are certain requirements that must be met before sprouting occurs. 

Did you know that every seed has an optimum range of soil temperatures for germination? This factor helps determine which seeds are cool-season versus warm-season. Penn State Extension has a great article regarding Soil Temperature and Seed Germination that you should spend a few minutes reading. 

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Worms! – The Garden Thyme Podcast

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In this month episode, we are chatting about the wonderful world of worms. Yes, worms. Although worms are slimy and wiggly, they play a vital role in our ecosystem. Earthworms increase air and water into the soil horizon, and usually, their presence is an indicator of a healthy soil system rich in nutrients and organic matter. Think of them as tiny tillers that incorporate organic matter, air, and water into the soil. 

Timing :
Ecology and Worms:~ 2:25
Vermicomposting: ~ 5:06
Invasive Jumping Worms: ~ 14:26
Native Plant of the month:  Black-eyed Susan’s- Rudbeckia ~ 22:25
Bug of the Month : Fire Flies/ Lightning bugs at ~29:10
Garden Tips of the Month at ~ 36:00

If you have any garden related questions please email us or look us up on Facebook

The Garden Thyme Podcast is a monthly podcast where we help you get down and dirty in your garden. The Garden Thyme Podcast is brought to you by the University of Maryland Extension. Hosts are Mikaela Boley- Senior Agent Associate (Talbot County) for Horticulture, Rachel Rhodes- Agent Associate for Horticulture (Queen Anne’s County), and Emily Zobel-Senior Agent Associate for Agriculture (Dorchester County).

Theme Song:  By Jason Inc

Beach Books for Veggie Gardeners

All right, maybe not the beach. But as we exit spring and enter the “oh maybe I’d rather stay indoors in the AC” season, I’ve got some recently-published books that might encourage you to get out there and make your garden better (but you can read them inside on a hot day and count that as horticultural education). Want to learn how to identify and deal with pests? Want to know if there’s anything to this “companion planting” stuff? And what’s up with “regenerative gardening”—can your soil really feed your plants? Read on!

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A gardener laments lessons hard won

If only I’d known.  How many times have we slapped our forehead at our gardening follies and mumbled that under our breath.  So today, I am paying homage to the lessons my garden has taught me.  

Soil is god. 

Healthy soil grows healthy plants.  So pay attention to your dirt, um, soil.  Feed it lots of organic matter:  compost, chipped leaves, grass clippings.  And be gentle with it.  Tilling destroys soil structure and harms the soil critters that make soil healthy.

Most bugs are good. 

Only one in ten insects is harmful. The rest are good guys that help control bad bugs.  And another thing.  The uglier the bug, the more beneficial it is.  Look up assassin bugs or cicada killer wasps.  Yikes.  

Assassin bug

Chemicals kill bugs good and bad. 

Most grab-and-go chemicals kill indiscriminately.  Do you really want to take out your allies? I think not. Choose less toxic organic products and do things like hand-picking and crop rotation to keep the bad boys at bay.

Right plant, right place. 

Placing plants where they can not only survive but thrive is smart.  Put a water-loving plant in hot, dry clay and it will die.  Guar-an-teed.  Find out what a plant needs and give it just that for great results.  Don’t tempt fate. 

Plant tags lie. 

Many plant tags have good information, but it goes only so far.  So, do a bit of research online or in a good gardening book to confirm what a plant needs as far as light, moisture, soil and space. 
My beautyberry is 4 feet wider and taller than its tag indicated.  

Respect frost dates. 

Yes, I know.  You want the first tomatoes on the block.  But if you plant them early and they get zapped, you have no tomatoes.  So wait to plant tender seedlings. Mid-May is good. Later is better if your area stays cooler longer.

Always lay garden rakes and pitchforks with the tines away and down. 

Enough said.  

Landscaping fabric is evil. 

Advertised as a weed block, this black devil mesh does nothing but give weeds something to sink their roots into.  Weeds grow both up and down through it.  You will spend half your life wrestling it out of your beds.  

Adopting sickly plants is a bad idea. 

There is a reason they look unwell.  Whether they have been watered too much or too little, baked or chilled, had too much or too little light, or beset by bugs or disease, avoid them.  Smart money is on the healthy plants.  

Impatiens with gray mold

What we do in our garden matters. 

From choosing organic bug controls to making compost, picking drought-tolerant plants to planting flowers for pollinators, every action we take has consequences.  Making earth-friendly choices makes our gardens and communities healthier. 

I hope the lessons my garden has taught me help you to avoid some pitfalls.  In gardening there are oh-so-many ways to get it right.  And wrong.  The fun is in the trying. 

By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension. This article was previously published by Herald-Mail Media. Read more by Annette.

Building healthy soil is the key to healthy plants

Healthy soil grows healthy plants.  If you want a vigorous, productive garden, protect and improve your soil.

Soil is made up of minerals, air, water, and organic matter.  This skin of the Earth anchors and grows our food, filters our water, and recycles vital nutrients like carbon.

How do you build healthier soil?  You feed it.

Compost, chipped leaves, untreated grass clippings, and other organic amendments can be turned in or used as mulch.  Cover crops can be planted in the fall and turned into the soil in spring.

This organic matter lightens heavy clay soils.  It improves soil structure.  It helps the soil hold water and nutrients.  It helps to suppress disease and feeds beneficial soil organisms.

Yes, soil is alive.  An intricate community of microbes, fungi, beneficial insects, worms and more lives beneath your feet. Keeping this gang happy helps your plants growing their best.

That’s why we discourage tilling.  When you till, you disturb the soil community, literally turning their world upside down.  You also damage soil structure and bring weed seeds to the surface.

So till less or not at all.  Instead, use a garden fork or broadfork to gently loosen soil, if needed. Broadforks are simply wide forks you rock to aerate soil.

Seedlings in soil

How else can you improve your soil?  Get a soil test.  For $10 to $15 you can find out just what fertilizer your soil needs – and doesn’t need.

Soil tests can save you time and money and keep excess fertilizers out of our waterways.

Getting a soil test is easy.  Download everything you need at the Home & Garden Information Center website.

Next, go deep.  Scoop a few soil samples in your garden, going at least 6 inches down.  Mix the sample and let it dry.  Scoop a cup or two into the bag, box it up, and mail it to a lab.

You’ll have your results in a week or two.  The test will tell you your soil’s pH, nutrient levels, and percent of organic matter.  You’ll also get specific fertilizer recommendations for what you’re growing.

You can also help keep soil healthy by not walking on it, especially when it’s wet.  That causes compaction.  Air, water, nutrients, and roots have a tough time moving through dense soil.

Instead, create paths or strategically place stepping stones so you can walk between rows of plants.

I know you’re eager to garden, but don’t work wet soil.  This also causes compaction.

To test if your soil is dry enough to work, grab a handful of and squeeze it into a ball.  Now, bounce it gently.  If it stays intact, your soil is too wet to work.  If it crumbles it’s ready.

And never, ever till wet soil.  That wrecks its structure and the soil community.  Think Armageddon.

Great gardens grow from the bottom up.  Protect and improve your soil to ensure it rewards you with year after year of productive plantings.

Photo of ornamental garden
Well-tended soil yields beautiful results such as the flowers at the Washington County Master Gardeners’ Boonsboro Library garden.

By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension. This article was previously published by Herald-Mail Media. Read more by Annette.

Planning and budgeting for a new raised bed garden

snowy landscape scene

Even though it is snowing again today, I am dreaming of gardening season and I am working on a budget for a new raised bed garden that will be 8’ x 4’ x 12”. I have always grown vegetables in a traditional in-ground garden, which only requires some tools for preparing the soil, soil amendments, and a suitable location (full sun with good soil). However, I want the advantages of a raised bed:

  1. earlier soil warming; 
  2. more focused usage of growing space (through succession planting and square foot gardening techniques);
  3. less body bending to plant, maintain, and harvest; and
  4. getting to plant cole crops sooner (with my in-ground garden, I have to wait until late May for the ground to be unfrozen and dry enough to run the the tractor tiller).
garden with a fence
Raised bed made from grapevines and a plastic liner.

A lot of inspiration can be found on the internet for building materials, but think about materials that you may already have on hand or something you can find freely or cheaply. More information on raised beds can be found on the University of Maryland Extension website. 

Some things to keep in mind:

  1. Natural materials (stones, logs, untreated lumber, cement blocks, sawmill slabs, bricks, etc.) are safe, affordable, and often can be scavenged/repurposed if you aren’t afraid to ask or do some physical labor. 
  2. What is your skill set? Maybe you can work out a trade with someone who can help you build the raised bed. 
  3. Any time you can buy items in bulk, you will save money.
garden sketch and seed catalogs

After doing some research, I plan to purchase new pine lumber from a local box store (easy to find and within my budget). Pine or softwood lumber should last anywhere from 3-5 years. Using commonly available sizes/dimensions, I will be spending approximately $80 (if it lasts 3 years, that’s $27 a year). Cedar boards would cost double the money but they could last closer to 15 years (cedar was out of stock in a lot of locations I checked).

Most stores that sell lumber will cut the lumber for no extra fee. It is sometimes cheaper to buy a longer board and have it cut into smaller pieces for transport. Be sure to plan ahead.

The most expensive part of creating this garden will be the topsoil, since I don’t have any extra in my landscape to use. The soil is an investment and will be a resource that I can use for many years to come to produce nutritious fruits and vegetables.   

raised bed vegetable garden

I used a free cubic feet calculator to figure out an estimate of how much soil I will have to purchase for my 8’ x 4’ x 12” garden. See the calculations below. 

cubic feet calculations

Soil is expensive and hard to transport and handle. I am prepared to do this step over the course of several days or have some people help me. Bagged topsoil usually isn’t the best quality and can add a lot of expense, but the source can be traced if any issue should arise, and also gives anyone with access to any vehicle type/transportation the ability to create a garden. Bulk topsoil and compost is usually sold by the ton or cubic yard, so the free calculators are helpful for figuring out amounts needed. Soil testing is recommended for raised bed gardens. 

            Soil Type         Price
Bagged Topsoil (43 bags of 0.75 cu foot)$110 
2/3 bagged topsoil, 1/3 bagged compost (45 bags)$145 
Bulk topsoil/compost$65   

The bottom line is that the raised bed could cost up to $225 depending on which option I use for soil. Using bagged soil/compost mixed ($145 + $80 lumber) is going to cost the most $225. If I use the bulk topsoil/compost option and use my own farm truck to haul it, it’s only $145. I’ve also budgeted an additional $40 for a 7ft deer fence and landscape fabric. For my family of 4, I am willing to count this raised bed garden as a worthwhile investment of time and money.

Have you used any interesting materials to create a raised bed garden? Do you have questions about a material that you can use to create a garden this season?  Ask your gardening questions here or share your story in the comments.

By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, Maryland, edited by Christa Carignan, Coordinator, Home & Garden Information Center, University of Maryland Extension. See more posts by Ashley and Christa.

Blueberry success is all in the soil

Farmers and gardeners learn much by daily tending soils and plants. But the winter “off-season” affords us time to dig deeper into topics of interest and learn from co-cultivators and experts in the field. I spent some time in a variety of grower meetings, conferences, and webinars in January and February where research findings were shared. Many gardeners are interested in growing blueberry so in this article I’ll share tips for success including some insights I picked up from presentations by Oregon blueberry researchers David Bryla, Ph.D. (USDA) and Bernadine Strik, Ph.D. (Oregon State U.)

Blueberry background

Highbush blueberry plants evolved to grow in low pH, high organic matter sandy soils with high water tables. These soils contain more ammonium nitrogen than nitrate nitrogen, hence blueberry’s preference for the ammonium form of plant-available nitrogen. The shallow, fibrous root system grows almost entirely in the top 12 inches of soil. Most of the roots are very fine, the width of a human hair, and can’t penetrate or thrive in clayey, compacted soils. The key to success is create garden conditions that mimic those in blueberry’s natural environment.

Blueberry thrives in well-drained, porous soils, high in organic matter (4% – 20%). The soil pH should be in the 4.5-5.5 range.

Soil preparation starts in fall

  • Begin by testing the soil in the late summer or fall prior to spring planting. For gardeners, soil testing labs provide the most accurate pH measurement of your soil, as well as baseline information on organic matter and nutrient levels. pH probes sold to gardeners are generally inaccurate and pH color kits using litmus paper are only accurate to ½ of a pH unit (5.5, 6.0, 6.5, 7.0, etc.

Add organic matter

  • The top 12 inches of soil should be one-third to one-half organic matter by volume. Peat moss (3.0-4.5 pH), plant-based compost (7.0-7.5 pH), and lightweight potting soil, a.k.a. soilless growing media (5.5-6.5 pH) are the materials most often mixed into the soil. Research has shown that adding compost (especially animal manure compost) can increase soil pH.
  • Some Oregon growers incorporate 2-3 inches of aged softwood sawdust into topsoil prior to planting. The benefit is that sawdust has a low pH, decomposes slowly, and increases organic matter levels. For Maryland gardeners, large amounts of sawdust are difficult to come by, but bark fines are readily available. You would need to apply 1.0 lb. of additional ammonium sulfate (21-0-0) per 100 sq. ft. nitrogen for the soil microbes that slowly decompose the bark fines.

Lower soil pH

  • Elemental sulfur is applied (based on soil test results) in the fall prior to spring planting, and incorporated to a 6-8 inch depth.
  • Pelletized and prilled forms of sulfur are easier to apply than powdered sulfur but take longer to lower soil pH.
  • An oxidation process, driven by special soil bacteria, converts the sulfur to sulfuric acid, releasing hydrogen ions that lower soil pH. The bacteria are most active in warm, moist soils. The process takes 6-12 months. Iron sulfate can also be used to lower soil pH but 6 times as much is required, increasing the cost.
  • Re-test soil pH to monitor pH levels and apply sulfur as needed to maintain the 4.5-5.5 range.
  • For container blueberry plants, mix 3 TBS. of sulfur into the top few inches of growing media, for a 15-gallon container, to reduce the pH by one unit (e.g. from 7.0 to 6.0).

Bag of sulfur
Elemental sulfur is available in powdered and pelleted forms


  • Ammonium sulfate fertilizer is recommended because it supplies nitrogen in the ammonium form and helps acidify the soil.
  • Fertilize at full bloom and again three weeks later.
  • Urea is another good nitrogen source, recommended when soil pH is below 5.0 because it is only one-half as acidifying as ammonium sulfate. The nitrogen in urea is converted to ammonia and then to ammonium.
  • Oregon research studies show that feathermeal (12-1-0.5) and soluble fish fertilizers (4-1-5) work well in organic blueberry production. Organic growers prefer to inject fertilizers into irrigation water, known as “fertigation.” Another interesting finding was that there were no significant yield differences between the lowest (20 lbs./acre) and highest (240 lbs./acre) nitrogen fertilization rates.
  • Organic matter and organic fertilizers release ammonium ions with relatively little oxidized to the nitrate form as long as soil pH is in the 4.5-5.5 range. When soil pH is >6.0 most of the nitrogen from decomposing organic matter will be converted to the nitrate form with negative effects on plant growth.
  • Oregon research indicates that organic acids (humic and fulvic) applied in liquid form, increase blueberry root growth while lowering soil pH.

Developing blueberries
Blueberry fruits developing


  • Blueberry root systems need to be kept moist. Plants can tolerate hot weather but not drought. Water your blueberry bed thoroughly and consistently when rainfall is lacking. Soaker hoses and drip irrigation work well.
  • Blueberry grows and produces best when the pH of irrigation water is <7.0. Commercial growers often acidify irrigation water to maintain low soil pH. The pH of municipal water in our region is typically 7.5-7.8 and has a high salts and bicarbonate content. Just be aware that your irrigation water can drive up soil pH.

Blueberry plants in large fabric bags
Blueberry plants in large fabric bags


  • Blueberry roots cannot compete very well with weeds for nutrients and water. Mulch is essential to keep soil cool, improve water infiltration, conserve soil moisture, reduce weeds, and increase organic matter.
  • Use aged wood chips (never fresh), shredded bark, pine needles, or sawdust as a mulch. These materials are low in pH (4.5-5.2) and salts, and decompose slowly.
  • Interestingly, a recommended growing system in Oregon uses strips of heavy-duty weed barrier to cover beds after they have been mulched to further reduce weed growth and moisture loss.

A well-planned and maintained blueberry bed can produce well for 20+ years. Start yours in 2021!


Lowering Soil pH for Horticulture Crops. Purdue Extension

Organic Blueberry Research–

Author: Jon Traunfeld, Extension Specialist