Robert Pavlis

Growing Streptocarpus: Planting Too Deep

The common advice for growing streptocarpus is to plant fairly shallow. Soil should not go much higher than the top of the root ball, or the plant will rot and die.

However, you are also told that to propagate the plant vegetatively, you should take a leaf or part of a leaf and plant it an inch or two deep. I usually plant these leaves about an inch deep, and they grow just fine.

Streptocarpus are also known to form plantlets from roots, deep in the pot (see image further down in this post). These grow underground for quite a long time before the tips reach above the surface of the soil.

How can all of this conflicting information be correct? Is this another Streptocarpus myth? I decided to test the claim that planting deep will cause Streptocarpus to rot and die.

small plant with three large pink and yellow flowers — Flowering streptocarpus RP193 from Experiment 25

Key Takeaways

Planting deeper will not kill a streptocarpus plant.

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Japanese Knotweed Myths & What Does Work?

Japanese knotweed is one of the most notorious invasive plants in temperate gardens—but it’s also one of the most misunderstood. Let’s bust some myths and explain the latest science on how to control it.

large shrub with light green leaves and dainty white flowers — Japanese Knotweed, source: Depositphotos

Key Takeaways

DIY solutions do not work.
Standard solutions used for other weeds also don’t work.
Herbicide spray works best, but it still takes a couple of years and has to be done correctly.

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Which Form of Nitrogen is Best for Plants

Nitrogen is one of the most important nutrients for plants because it is almost always in short supply. The amount of nitrogen available controls plant growth.

Synthetic fertilizer usually supplies nitrogen as urea or nitrate. Organic fertilizer supplies it as proteins and amino acids, and they claim these forms are better for plants. Which forms of nitrogen can plants use, and which is the best form for gardeners to use for growing plants?

diagram showing the movement of nitrogen from one form to another. — Nitrogen cycle, source: Depositphotos

Key Takeaways

Nitrate and ammonium are the main forms of nitrogen used by plants.
Plants can use urea and amino acids directly.
Plants also seem to be able to digest proteins and then absorb them through roots, probably as amino acids.
Organic gardening techniques don’t seem to significantly alter the amino acids in soil.

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Do Lettuce Seeds Need Light to Germinate?

A lot of specialty seeds need light to germinate, but it never occurred to me that vegetable seeds might need light until a couple of months ago, when I read that lettuce needs light. I have always covered my lettuce seed, and it germinated just fine. How can that be if they need light?

How much light do they need? Does a thin covering of soil allow enough light to reach them?

I decided to do some tests to figure things out, and that just made the picture murkier. Here are my test results and information from a number of scientific studies. The answer is not what you think.

guy planting lettuce seedlings — Planting lettuce seedlings, source: Depositphotos

Key Takeaways

Lettuce seeds can germinate in the dark.
The light requirement for germination depends on the cultivar.

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Fertilizer in Potting Soil – Good or Bad?

In the good old days, commercial potting soil (media) contained no added fertilizer. Today, more and more products contain some fertilizer, either in synthetic or organic form. Gardeners have been led to believe they can fertilize less and skip fertilizing seedlings. Some believe they can stop fertilizing houseplants entirely. But no one seems to discuss the elephant in the room!

How much fertilizer has been added? Should you stop fertilizing? When does the added fertilizer run out? How quickly are the nutrients available to plants? This blog will answer these and other questions about this mysterious fertilizer.

girl repotting some houseplants — Do you need to fertilize potting media source: Depositphotos

Key Takeaways

Potting soil manufacturers don’t provide adequate information about their products.
The fertilizer in these products is too low to grow plants.
Repotted plants, including seedlings, should be fertilized right away.

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Fertilizer PPM Calculator

Gardeners normally talk about “teaspoons” of fertilizer when they make up fertilizer solutions, which leads to all kinds of confusion and misuse of fertilizer. Some of you are using too little, while others use way too much. On the other hand, horticultural professionals don’t make these mistakes because they talk about PPM values instead.

It’s time gardeners change their habits. Start using Parts Per Million (PPM) units instead of teaspoons in your discussions. This will improve online information and reduce your fertilizer mistakes. I discussed the reasons for doing this, along with several examples, in Calculating the PPM of Nitrogen in Your Fertilizer.

To help you use ppm values, I have created this simple-to-use Fertilizer PPM Calculator, which shows you how much fertilizer to use to make up a required ppm solution. It works for both metric and imperial units, and can be used for both solid and liquid fertilizers.

plant in soil while fertilizer is added to the soil — Fertilizer PPM Calculator, source: Depositphotos

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Can Monarchs Smell Milkweed From 2 Miles Away?

Monarch butterflies and milkweed plants share a special bond. Monarchs rely on milkweed to lay their eggs and feed their caterpillars. For gardeners and conservationists wanting to support these beautiful insects, understanding how monarchs find milkweed is key. A common claim pops up: Can monarch butterflies smell milkweed from 2 miles away? Let’s explore what science says about this remarkable relationship.

Monarch landing on the pick flower of a milkweed — Monarch landing on Swamp milkweed (*Asclepias incarnata*), source: Depositphotos

Key Takeaways

Monarchs do NOT smell plants 2 miles away.
They use sight and smell to find milkweed 100-200 feet away.
Monarchs do use their feet to taste plants once they land.

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Does Rainwater Make Plants Greener?

Many gardeners have noticed that grass is greener and plants look healthier after a good rain. They conclude that rainwater is better for gardens than tap water. Is that really true? Is rainwater better than tap water? Does rainwater make our gardens greener? Let’s open that umbrella and find out. Key Takeaways Are Plants Greener … Read More

Does Rain Add Nitrogen to The Garden?

Gardeners claim that nitrogen levels in the soil increase after rain. Water floating down through the air picks up nitrogen and deposits it on and near plants. Lighting adds even more nitrogen to the process. They base their conclusion on the perceived greening of the garden after a rain. In agriculture, it is well understood … Read More

How Much Light is Best For Tomato Seedlings?

How much light should tomato seedlings get? If you give them too little, they will become tall, skinny, unhealthy plants, a condition called leggy. If you give them too much, the leaves will be damaged. How much is the best amount?

The new science of growing tomato seedlings will surprise you.

12 tomato seedlings with several red tomatoes in front. — Tomatoes and tomato seedlings, source: Depositphotos

Key Takeaways

Tomato seedlings grow best with a PPFD of 250 to 300.
A DLI of 10 to 13 works best.
All plant seedlings need 8 hours of darkness.

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Should You Use Drainage in Your Pots?

It used to be very common to add drainage material, such as rocks, Leca, or clay pot shards in the bottom of pots for added drainage. Then it was claimed that this is a myth and it does not work. But then some new science this year upsets everything by showing drainage material may actually work.

Should a gardener use drainage material? What kind of material works best?

lady's hand putting leca beads into a pot. — Leca being added to the bottom of a pot of succulents, source: Depositphotos

Key Takeaways

Drainage material reduces the water in the soil.
It is best not to use drainage material in most cases, but it can be useful in the right situation.

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Does Gravel in Pots Increase Drainage – The Latest Science

Logic would have you believe that adding gravel or pot shards in the bottom of a pot or container will increase drainage and this has been a common practice for a long time. More recently some gardening experts and scientists have declared this to be a myth, claiming that gravel does not increase drainage when placed in the bottom of a pot. That is the current thinking.

New science has now been published that debunks the claimed myth and concludes that drainage material in the bottom of a pot or container does increase drainage.

Does Gravel in Pots and Containers Increase Drainage? source: North Dakota State University

Key Takeaways

New science shows that drainage material in the bottom of a pot increases drainage.
Highly porous soils are affected more.
Sand at 60 mm worked best.

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