Soil Needs for Planting Astrid Muschalla

Astrid Muschalla is coordinator of 1000 Islands Master Gardeners. She is a Master Gardener, a trained volunteer in horticulture.

Astrid highlighted some key planting principles and suggested soil amendments when planting. She also gave tips for dealing with specific plant packaging, planting bare root plants, planting trees, and pruning a young plant.  Finally, there were your questions and a reminder of upcoming events.

Key planting principles

Check the soil temperature

Check soil temperature (using a soil thermometer). For cool season crops soil should be at least 10 C and for warmer season, sun loving crops like peppers, tomatoes and beans, 15 C. If the soil is too cold, the seeds won’t germinate, and plants will be stressed.

Be familiar with the planting location and typical water saturation

Avoid planting in wet and waterlogged soil. Digging leads to soil compaction. 

Tip: Cover the area typically wet in the spring with a plastic layer one month before planting. This will prevent saturation and allow for earlier planting.

Best time of day to plant

Avoid planting in the hot midday. Hot sun and wind quickly dry out the tiny delicate root hairs of young plants. These roots are critical for nutrition absorbtion. 

The planting hole

Dig a hole in the soil twice as wide as it is deep. Width is important not depth. 

Encouraging/stimulating healthy root growth

The aim when planting is to get maximum root establishment before the dry season (July and August). This will allow for greater plant resilience. Plants may go dormant but they won’t die during a drought. Once established, plants need 1/4 inch of water per week to survive. The water keeps the soil alive which in turn keeps the plants alive.

Typically, nursery plants are grown in a medium that is light and may include perlite, vermiculite and/or peat. The soil on your property will be very different, some mix of sand, silt and/or clay.  The growing medium tends to dry out and will wick moisture away from the root ball once planted.  When planting, remove as much of the growing medium as possible from the root ball. Wash this off gently with a hose or place in a pail and dunk a few times to loosen. This will allow you to place your new plants’ roots directly into the native soil, and encourage better root growth. See suggestions for dealing with specific plant containers below.

Soil amendments when planting 

Astrid recommends that you add a mycorrhizal inoculant, otherwise referred to as effective microorganisms (EM). It comes in a light powder and contains beneficial fungi that co-exist and work symbiotically with the plant in its native habitat. The fungi facilitate absorption of phosphorous and other trace nutrients by the plant, and the plant supplies the fungi with nutrition through photosynthesis. Water sharing also occurs. This inoculant is especially helpful if working in degraded, compacted or waterlogged soils. It is the first line of defence against plant disease. Note, the spores of the inoculant are only activated once in contact with the roots. Studies have shown that amending the soil in this way decreases mortality of new plants from 30% to around 6%.

Other recommended amendments include worm castings and seaweed. Such amendments can be used for annuals like geraniums as well as large root ball plants. 

Soak the root ball with compost or seaweed and the mycorrhizal inoculant in water, before planting.  You can also soak your plant in a tea using good quality compost if you don’t have anything else at hand.

For gardens harvested regularly, like vegetable gardens, supplement the soil with volcanic pulverized minerals. This is untreated and crushed and contains small amounts of trace elements. It is only effective where the soil microbiology is good, as this is what makes the minerals available to the plants. Remember, soil microbes need organic matter to survive.  Another option is Azomite. These supplements can be used without soil testing.

If you add commercial supplements like calcium, phosphorous or potassium, a soil test is vital, as the concentration of these elements is high and if applied incorrectly can damage the balance in your soil. 

Sources of supplements:

Kingston Organics & Hydroponics (seaweed and bags of worm castings)

Gardener’s Pantry online

Potters Nurseries

Tips for dealing with plant packaging

  • Peat pots – these are slow to decay and need lots of moisture. This may be too much for your plants and they can rot. The plants can also dry out if the top of the pot sticks up and wicks the water out and away from the root ball. When planting, rip off the top of the pot that will stick up above the ground. 
  • Balled and burlapped plants – Burlap is very slow to decompose and will constrict root growth. Remove all string and burlap. If your plant is heavy, position it in the hole, cut the burlap off the sides of the root ball. Remove as much as possible and what you can’t remove, lay down into the hole. 
  • Wire baskets – usually used for big trees. Remove the cage or the roots will be girdled. As with burlap, remove what you can and lay the rest down in the hole. Note that trees don’t die overnight, they take a long time to show their distress. 
  • Plastic pots – can be root bound.  When purchasing a potted plant, pull it out of the pot to examine the roots. Avoid buying plants with strong large circling roots. That is a strangulation pattern of growth that will not correct itself in your soil. A large plant in a small pot is a clue that this may be a problem.

White roots are active root hairs and will grow. Black ones are dead and can be cut out. You can encourage roots to grow out rather than in a continuous circle as trained in the pot by gently teasing the roots loose. If they are more dense, cut four vertical slits down the root ball, and an X on the bottom of the pot. Flare out the roots to stimulate outward root growth. Use a sharp knife or saw to cut rather than  tear with your fingers. 

General note: Annuals/perennials from nursery stock are started early and tend to be root bound by the time they are sold. Plant as soon as possible after the last frost. 

How to plant bare root plants

Bare root plants are dug out of the field when dormant. Soak 12 to 24 hours before planting. Add seaweed and effective microorganisms (EM) or good compost (if that is all you have on hand) to the water. If you are not ready to plant immediately heel them in i.e. lay the ends in a trench and cover with soil until ready.

Planting trees

When planting trees identify the root flare, a slightly thicker area around the root zone. This must be 1 to 2 inches above the ground. To avoid planting too deep as the soil settles, dig the hole 90 to 95% of the depth of the root ball.  If, once you have planted, you notice too much settling, pull out and add more soil beneath the root ball.  Backfill the hole with native soil and mulch the area. A mulch circle prevents competition for the trees’ feeder roots from weeds and other plant growth. It also protects the trunk from damage from a mower or whipper snipper. Make sure the mulch does not touch the trunk of the tree.

Did you know: Grass around a tree is allelopathic, it can kill small trees. 

In the first two years water the tree carefully.  During this time most of the growth takes place below the surface. In the third and fourth years, you’ll see growth above the ground. 


  • Landscape fabric around trees. It reduces water infiltration and there is no nutrient cycle from mulch.  Fabric is good for hardscaping; bricks or patio stones. 
  • Rocks under tree. Rocks don’t feed the tree and over time weed seeds blow into the crevices. Weeding in rocks in difficult and labor intensive. 

Staking trees

Only use stakes in the following circumstances:

  • Your tree is big and unstable
  • You are planting bare root.
  • In a high wind area
  • Where there is a risk of vandalism (e.g. parks)

Stakes should be flexible and allow 6 to 10 inches of sway. This enables the tree trunk to strengthen. Prevention of sway will weaken the plant. If you are only using one stake, place it upwind (West) of the plant. Ties should be broad and smooth. Do not use rope or wire/wire in rubber tubing. This can damage the plant. Remove all support after two years max.

Pruning a young plant

Prune if you want a bushy plant or more flowers/leaves, such as basil or marigold. Cut with scissors or pinch (if very tender) just before a leaf node of the main branch and the lower branches if they are sturdy. In the case of basil for example, you can encourage more leafing by removing the flowers too. At each point that you prune, two new stems will grow. 

That kind of pruning doesn’t work on all plants – i.e. tomatoes should have a strong main stem so don’t prune the main tip, just prune out the side suckers from the main stem.

For more information on pruning visit the Rideau Thousand Islands Master Gardener website. 


Is it safe to remove rocks from the base of an older more established tree?

The active feeder roots of a tree are at the drip line (the edge of the horizontal tree branches) which extends as the tree grows. The woody roots closer to the tree help stabilize the tree. This means that closer to the tree you can add up to 8 inches of soil and plant Hosta or other shade loving perennials or annuals. It is important not to cover the roots too deeply as air circulation is important. The best however is to add mulch around a tree to the drip line.

Are fertilizer spikes good for mature evergreen trees?

The best fertilizer for trees is leaves. If, however, the tree is in an area where all leaves and twigs are removed every year the soil is most likely sterile. In this case fertilizer spikes will help. Fertilizer spikes tend to be salty and thus harm the fungi in a healthy soil. 

Will hen manure (used to keep squirrels away from the garden) add too much calcium to the soil?

If it is bought already composted it will do no harm. 

When is the best time to correct planting mistakes made last fall?

Correct as soon as possible. Dig a little away from the root ball and gently manoeuvre it up with your hand or a shovel to add soil below if it is planted too deeply. 

When planting bareroot, the depth of the planting is important (root flare). Even if they look dead, don’t remove them yet. Wait a few weeks, they may still be dormant and send a new shoot from a dormant bud at the stem. 

What is the shelf life of mycorrhizal powder?

It lasts about two years. You will find an expiration date on the package. Store in the basement not in the garage where it will freeze.

Can I keep suckers at the base of a Serviceberry tree to have fruit low down?

Suckers don’t form in the same way as natural branches. They tend to be weaker. On a smaller plant like a Serviceberry it would be ok to keep them, but not on a larger tree. 

What is the best mulch for trees and gardens?

Leaves and fresh wood chips. Leaf piles that have sat over the fall and winter make great mulch at this time. Avoid purchasing bark. Rather use fresh arborist wood chips. These are nutritious and can be composted also. 

Are soapsuds effective to get rid of pests eating plant leaves?

Soap degrades the waxy coating on leaves, so while it may initially appear effective over the longer run the plant becomes more vulnerable. Ideally, water and provide good nutrition for the plant and it will be strong enough to deal with the pests itself. You can give your plant a “pick me up” tonic. Soak a good quality vermicompost in water for a half hour and use to water the plant. 

 A row of 15 year old Colorado Blue Spruce are becoming thinner on the bottom especially on the north side – is this normal?

The North side of the tree gets the least amount of sun. It is also usual that the lower needles will brown and drop off.  For a bushier plant: 

  • water with a compost slurry or drink booster
  • prune the new branch tips by half once the tips elongate – usually first week in June or end of May. 

Upcoming events

If you’d like to learn more about vegetable gardening from Janette Haase, author of From Seed to Table: A Practical Guide to Eating and Growing Green,  register for her Monday afternoon coaching sessions on Zoom.

If you’re not already registered, join our next Master Gardener Zoom Q & A on Eventbrite

Thought for the day:

Grow it….Don’t mow it 😊

And plant vegetables instead of flowers this year.

Happy gardening!

Reporting by Colette McKinnon, Master Gardener in Training, Rideau 1000 Island Master Gardeners