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8 Common Basil Growing Problems

Common problems in growing basil.

Basil is an herb that is commonly used in a lot of Italian and Mediterranean cooking, but the herb can also be used for a lot of different medicinal and practical purposes around the house.  Basil comes in several different varieties, with each type imparting it’s own unique flavor such as cinnamon basil or spicy Thai basil.

For these reasons, most gardeners like to grow some basil in their indoor or outdoor gardens.  When the plant starts having problems, however, it can really affect the amount of basil that is available to be harvested.  

If the plant dies, it can take about two months to have leaves ready for harvest if you have to restart from seed.  For many gardeners, that’s why it makes sense to try to treat the problems their basil plant is having rather than just pull the plant and restart.  Fortunately, most solutions are relatively easy to implement.

1.  Too few leaves

A leggy basil plants with few leaves.

This is commonly referred to as being too leggy.  The value of growing basil is in harvesting the leaves, which is why a basil that grows very high stems with small leaves might be a healthy plant, but not a particularly useful one.  

The cause of this problem is usually over-fertilization.  Commercial fertilizers are designed to get plants to grow quickly, and in the case of leggy basil, the plant will usually grow to full height in less than a month.  Leaves take time to develop, however, making the plant appear as if the leaves are not growing.  In reality, the leaves are growing as fast as they would have without fertilizer, but the increased size of the plant makes it appear as if the leaves are too small.

The problem here is that the leaves are in fact too small to make enough food to fully support the plant.  The leaves themselves, because they are not fully-developed, will be lower quality leaves with less of the oils that give them their flavor.  Fortunately, there are a few ways to deal with the issue.

a.  Bring down the fertilizer gradually

Completely stopping fertilizer if the plant is in really bad shape can result in a quick die-off of most of the plant, as the leaves will not be able to support the entire plant.  Add about half the recommended amount of fertilizer to continue to support the plant until the leaves are in good enough shape to support the rest of the plant.

b.  Once the leaves are big enough to support the plant, wait a few weeks before harvesting

 When you do harvest, take only the leaves that are damaged.  Leave the healthy ones to support the plant until it makes a full recovery. In the future, do not overfertilize basil.  If you want it to grow faster, mix a high amount of compost into the soil before planting.

2.  Temperature drop

A dying basil plants in a pot.

Basil likes to grow in a warm climate, and it can be particularly sensitive to cold snaps.  If your basil was planted outside and experienced a sudden temperature drop, it likely started dropping leaves fairly fast.  After the leaf drop, it’s not uncommon for the plant to bolt up, leaving you with a leggy basil plant and nothing to harvest.  

To fix this, trim off everything on the plant that is showing signs of frostbite.  This will likely mean that you have to trim the taller stems on the plant.  While this will stunt the growth in the short term, it is a good thing for the plant in the long term.

3.  Not enough sunlight

A dying indoor basil plants in a black pot

In addition to warmer temperatures, basil likes to get at least six hours of full sun everyday.  If your plant is in too much shade, it’s very likely that it is looking sickly.  In truth, the plant is actually sickly, but it is growing towards whatever light it can find.  This often results in a plant that looks very lopsided or leans.  Leaves will only tend to grow on the side that gets enough sunlight.

The most direct way to solve this issue is to transplant the whole plant into a sunnier area.  Otherwise, look for ways to reduce the amount of shade the plant is in, such as trimming back surrounding branches and bushes that are providing shade.

 Once you’ve established the plant in good sunlight, prune back any leaves and stems that are yellow or brown, and consider pruning back any parts that have grown too tall.  This will encourage the plant to grow out and produce more harvestable leaves rather than grow up.

4.  Over Watering

Water is dripping heavily on the basil plants.

Basil tends to react poorly to having too much water around its roots.  Whether you’re over-watering or the soil has poor drainage, basil will be affected by being in too much water with root rot.  

Since you can’t see the roots, the first signs that there is a problem will be when the plant’s leaves and stems start to turn brown and fall off or die back.  This occurs because the plant’s roots cannot get enough nutrition to the upper parts of the plant.

Unfortunately, there isn’t a lot that can be done about overwatering or root rot.  If the plant is just slightly water-logged odds are that it will recover on its own once the soil around it starts to dry.  If root rot has completely set in, however, there isn’t much that can be done.  

Sometimes aggressively pruning back the plant will help, as healthier parts of the roots are able to support a smaller plant, but be prepared to lose the plant.

In particular, snip off any leaves and stems that are already starting to die; these parts of the plants are already unable to receive nutrition, and it will help the plant to remove the diseased parts and focus on building the health of the main plant.

5.  Underwatering

A dry and yellowish basil plants in garden.

If your basil plant hasn’t received enough water, it will likely have issues with leaves turning yellow, then shriveling and turning brown before eventually falling off.  Fortunately, basil is a plant that tends to recover quickly after short periods of drought.

 If you haven’t received enough rain in your outdoor garden, or if you just forgot to water your plant, odds are good that your basil will recover. A few words about watering though. To start, basil tends to do best when the soil around it is watered.

Try to avoid pouring water directly on top of the plant, and especially try to avoid drowning the leaves.  Like many other plants with broad leaves, it is easy for moisture to get trapped inside the curls of leaves and start rotting the leaves.  This is especially the case with basil that is grown in partial shade.  

Keep the soil around your basil plant moist; in fact, it’s a good idea to water the plant as soon as the soil starts to appear dry.  Again, remember to pour the water directly onto the ground, and stop once the soil appears wet.

6.  Lack of Pruning

An overgrown basil plants in garden.

It can seem almost counterintuitive to remove the leaves of a plant in order to get it to grow more, but it really is the best way to get basil to produce more harvestable  leaves.  In the early growth stage of the plant, the common advice is to pick leaves as needed; even on a new plant this should be enough to stimulate growth.

Personally, I find it hard to determine how much to harvest from a plant like basil, so I try to follow the 10% rule.  No matter how often you harvest an herb, never take more than 10% of the plant in a single day.

Following this rule usually ensures that you’ll have enough leaves per day to cook with for your family, but it also allows the plant enough left over leaves to keep the plant healthy.  When following this rule, you don’t have to worry about which leaves to pull. If you clip a single large leaf or several smaller ones, the plant will stay just as healthy as it was before.

In all the years I’ve grown basil, I’ve been able to maintain healthy plants for years by never taking more than 10% of the leaves in a single day. Of course, this can be a very time-consuming rule if you need to harvest your plants for a large meal, to sell the leaves at a farmer’s market, or to dry out the leaves for use later.

While there are plenty of home gardeners who take the time to harvest a few leaves from each plant everyday, then take the time to individually dry everything, it is important to know how to harvest a lot of basil at one time and maintain the health of your plant.

To harvest a large amount of basil, use pruning shears to cut the top stems and leaves off of the plant.  The top tends to be the most recent growth, and the plant will be able to grow out from the leaves and stems that are remaining.  Pull individual leaves off of what you cut off to use in recipes or dry; compost the stems.

Next, remove all of the large leaves from the remaining plant.  Large leaves tend to block sunlight from reaching the smaller leaves, making it difficult for them to be healthy and grow.  The remaining plant will have small leaves, but it will grow quickly (if the plant is healthy) and it should be ready to harvest again within a month.

7.  Over Pruning

A hand pruning a small basil plant in a pot.

If you have never pruned your basil plant before, it’s entirely possible that you trimmed it too far back when you decided to harvest.  Without any leaves, it will take basil a long time to process the sunlight it needs to keep a complex root system going through the stem alone.  

While this will not typically kill the plant, it may take several months for the plant to recover to the point that it can be harvested again.

In general, I recommend the 10% method to new gardeners in order to avoid this problem.  By taking no more than 10% of the leaves on a plant per day, it’s almost guaranteed that you will not have issues with over pruning.  Even if you have already trimmed the plant back too far, this method will ensure that you do not repeat the mistake.

8.  Bolting

An outdoor basil plants with flower buds.

If you allow basil to get too tall, it will start to grow flowers.  The flowers will eventually grow seeds, but once this happens the basil leaves will turn bitter and will no longer be good for cooking.  

To avoid this problem, prune the plant regularly.  Ideally, cut leaves and stems from the top part of the basil. This will encourage the growth of more leaves, and force the basil plant to spread out rather than grow up.  Don’t be afraid to cut the entire top part off of the plant; this is the best way to ensure that the basil does not bolt.

If you are nervous about taking too much at one time, remove 10% of the top part of the plant everyday until the plant is back down to a more manageable size and the danger of bolting is passed.

If you have made the mistake of allowing the plant to form flowers, it’s probably too late to save the existing leaves.  Some gardeners will remove the flowers as soon as they see them, but depending on the exact variety of basil you’ve planted this will have mixed results.  

Sometimes it will stop the production of flowers altogether, other times it will encourage their growth.  My recommendation is to allow the plant to produce seeds, then start all over again with new basil plants. 

The leaves of a basil plant that has bolted will not taste as good as they otherwise would have, but they can still be used for poultices and the oil and leaves can be used as an anti-bacterial agent.

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