Ask a Gardener is a seasonal advice column written by BBG gardener Laura Powell.
What are some natural ways to improve soil fertility without using chemical fertilizers?
Soyan, Staten Island, NY
Dear Soyan,
Investing in your soil is one of the most significant steps you can take to maintain a healthy garden. There are plenty of ways to do so organically.
Whether your gardening space is new or established, a great way to improve soil fertility is to add compost. If you are working in a new space, you can mix the compost into the soil, but if you have an established garden and don’t want to disturb the soil, you can just spread a layer on top. (This is called “top dressing.”) The organisms that live in your soil will move the compost around over time.
Compost can do so much for your garden, including giving your plants a boost of nutrition, improving your soil structure, and improving the microbial activity in your soil. (Composted manure, though sometimes harder to come by, is another option that serves the same purpose.) Top dress in the spring or fall when plants are actively growing. A quarter or a half-inch layer twice a year is a great addition to most gardens.
Mulching is another way to improve soil fertility. The mulch (which can be composed of a variety of materials, including dried leaves and dead plants) will decompose over time, slowly adding nutrients and feeding your soil microbiome. It acts a lot like compost in your garden, just over a longer time period.
If you’re growing annual crops, like vegetables, crop rotation is another option. Different crops have different nutrient needs and rotating crops to different areas of your garden will help reduce the likelihood of your soil getting depleted of certain nutrients. Crop rotation is most effective when used in addition to organic soil amendments like compost.
Finally, consider cover cropping. This method is suitable for an annual garden, because it is done during your off-season. The way it works is you plant a soil-enriching annual crop like winter rye or crimson clover during the time when your soil would usually be bare—generally winter time for vegetable gardens in the Northeast.
These crops are not harvested, but instead are tilled into the soil or just cut down and left as mulch. If you decide to cut it down and leave it as mulch, you can plant into the area as you would in any mulched area, by pulling the mulch back before planting, and then spreading the mulch around the plants after planting. It’s important to cut down your cover crop before it goes to seed, because you don’t want to have a garden full of cover crop seedlings!
I was given a redbud sapling as a gift. Where do these trees grow best, and how should I care for it?
Michele, Acton, MA
Dear Michele,
A redbud tree is a lovely gift!
There are several species with the common name redbud, but the most common one in our region is Cercis canadensis, or Eastern redbud, which is native to the Eastern United States. It is a small tree in the Fabaceae (legume) family with purplish pink flowers in the spring and beautiful heart-shaped leaves all season long. This species has an important legacy of use by Indigenous communities, from food (its flowers and seed pods are edible) to medicines.
As for where these trees grow best, Cercis canadensis is a fairly adaptable plant and will grow in a range of soils from clay to sandy, though it will thrive best in moist, well-drained soil. It will grow in either full sun or partial shade—it will bloom more if planted in full sun, but it will also need to be watered more often. The mature size of Cercis canadensis is 20–30 feet tall and 15–30 feet wide, so wherever you plant it, make sure it has room to grow.
Redbuds are pretty tough plants, and since they are native, they are well-suited to our soil and climate. After planting, water it regularly. How frequently you water will depend on the weather, but make sure to water thoroughly when you do. Apply a 2–3 inch layer of mulch at the base of the tree (taking care not to pile against the trunk) to help conserve moisture in the soil.
Given these conditions and care, your sapling will grow into a beautiful tree, and will likely begin blooming when it is 4–6 years old. Enjoy!
How do I deal with pests and insects without using harmful chemicals?
Rudra, Brooklyn, NY
Dear Rudra,
It is entirely possible for a home gardener to avoid using chemical pesticides.
The first step is to focus on improving the overall health of your plants. Did you know that some herbivorous insects are specifically attracted to plants that are stressed? Healthy plants are also able to weather many threats that harmful organisms present.
A few ways to support your plants’ health:
- Make sure they are planted in the appropriate cultural conditions (for example, plant sun-loving plants in full sun, shade-loving plants in shade).
- Don’t space plants too closely together (proper spacing allows for air circulation, reducing the spread of fungal infections).
- Water properly (remember that overwatering can be as stressful as underwatering for many plants).
- Maintain soil health (see previous question).
Next, include a diverse selection of plants in your gardening space. Diversity can make your garden more resilient, because there will always be some plants that are resistant to a given stressor.
When selecting plants for your garden, be sure to include some plants that attract beneficial insects like ladybugs or lacewings. These “beneficials” feed on aphids, mealybugs, and other common garden pests. Yarrow, dill, and cosmos all attract beneficial insects and are beautiful additions to a garden.
Take the time to learn what the beneficial insects in your area look like. This way, you’ll know which insects on your plants are helping your garden.
Physical protections like row covers can also provide protection from insects and other nibbling visitors. For larger insects like caterpillars, you can hand pick them off your plants instead of spraying chemicals. And removing dead plants and debris promptly can reduce certain pests’ ability to hide and reproduce.
I recommend thinking of your garden as an ever-changing ecosystem. Some creatures that feed on plants, like aphids, are a necessary part of that ecosystem. For example, aphids are food for lacewing larvae and parasitoid wasps.
Which brings us to the most important piece of advice for avoiding the use of harmful chemicals: Let go of perfection. As long as your gardening space is healthy overall, a little bit of damage is normal.
Got a question for Laura? Submit questions for our fall installment of Ask a Gardener using the form below.
