In certain instances such as after a failed seeding, winterkill or in an attempt to thicken thinning stands, producers may be interested in following alfalfa with alfalfa. This practice has met with varied success due primarily to compounds produced by older alfalfa plants, which inhibit the growth of young seedlings. This process is known as autotoxicity. In this Focus on Forage, we will discuss what causes autotoxicity, factors that affect it, and ways to reduce the effect.
Plants produce a wide range of chemicals aimed at defending them from attack by insects and diseases. These compounds are called secondary metabolites, as they have no metabolic function in the plant except as a defensive mechanism. Among these chemicals are some that inhibit the growth of other plant species. The production of compounds by one plant species that are toxic to another is known as allelopathy. The production of chemical compounds by a plant that are toxic to members of the same species is known as autotoxicity. Plants produce these compounds to help “carve out” a space for themselves and reduce competition from other plants for water, nutrients and light. Alfalfa is a plant species that exhibits autotoxicity.
There are a number of potentially autotoxic chemicals produced by alfalfa, one of which is called medicarpin. This compound is present throughout the plant but is more concentrated in top growth than roots. It is a water soluble compound that leaches readily into the soil from both decomposing plant material and growing plants.
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Alfalfa, also known as lucerne, is a versatile and nutritious plant commonly grown for livestock feed. However, alfalfa can also thrive as a houseplant, providing lush green foliage to brighten up any indoor space. As your alfalfa plant grows, it will eventually outgrow its pot and need repotting to support continued healthy growth. Repotting gives the roots more room to spread out and access fresh nutrients. Follow this simple guide to successfully repot your alfalfa houseplant.
When to Repot an Alfalfa Plant
Plan to repot your alfalfa houseplant every 1-2 years or whenever you notice signs of being rootbound, such as slowed growth or roots protruding from the drainage holes. Spring and early summer, during the active growing season, is the ideal time for repotting. This gives the plant time to recover from transplant shock and establish in its new container before winter dormancy. Avoid repotting during the fall and winter months.
Choosing the Right Pot Size
Select a pot that is 1-2 inches wider in diameter than the current container. Gradually increasing pot size allows room for root growth without overwhelming the plant. Ensure the new pot has drainage holes to prevent soggy soil. Terracotta, plastic, ceramic, and glazed pots all work well for alfalfa. Match the pot style to your home décor.
How to Repot an Alfalfa Plant Step-by-Step
Follow these simple steps for stress-free repotting
Gather Supplies
Before starting have these supplies on hand
- New pot with drainage holes
- Trowel or small shovel
- Fresh general purpose potting soil
- Watering can
- Gardening gloves (optional)
Remove the Plant from Its Pot
- Tip the pot on its side and gently slide the plant out. Alternatively, hold the base of the plant and turn the pot upside down, tapping gently to loosen.
- Handle the plant carefully to avoid damaging the stem and root ball.
Inspect and Prune Roots
- Examine the root system, trimming any diseased, dead, or excessively long roots with clean pruners. This encourages new root growth.
- Also remove any circled or matted roots around the edge.
Prepare New Pot
- Place a 2-3 inch layer of fresh, dry potting soil into the bottom of the new container.
Reposition the Plant
- Place the alfalfa plant into the center of the new pot. The root ball should sit level with the soil surface.
- Begin filling around the plant with more fresh soil. Tamp it down gently to remove air pockets.
Water Thoroughly
- Water well until it drains from the base after repotting. This helps settle the soil. Avoid fertilizing immediately after repotting.
Caring For Your Alfalfa After Repotting
- Set the newly potted alfalfa in a spot with bright indirect light. Maintain evenly moist soil.
- Monitor for signs of transplant shock like drooping leaves. Water lightly if needed.
- Resume normal care routines after a week or two once established. Fertilize every 2-3 months during the growing season.
Transplanting Outdoors
For transferring alfalfa into the garden
- Harden off indoor plants for 7-10 days before transplanting outside. Slowly introduce to sun and wind.
- Prepare garden beds with compost and a 10-10-10 fertilizer before planting.
- Space plants 12-18 inches apart in rows set 2-3 feet between.
- Dig holes the depth of each root ball. Place plants at the same level as they were growing in pots.
- Water immediately after transplanting and daily for the first week until roots establish.
With the right care while repotting and after, your alfalfa houseplant will quickly bounce back from transplant shock. Pay close attention in the weeks following to ensure your plant adjusts well. With room to stretch out its roots and fresh nutrients, your alfalfa will continue growing happily in its new home.
How can autotoxicity be reduced?
The best way to avoid autotoxicity is to rotate to some other crop such as corn for at least a year before seeding the same field back to alfalfa. This gives the toxins time to be degraded, leached, or otherwise removed from the soil environment. If alfalfa must follow alfalfa, the best choice is to kill the old alfalfa in the year prior to seeding. The degree of toxicity is directly related to the amount of time between killing the old stand and establishing the new stand.
If alfalfa must be planted in the same year an old stand is killed, a late-summer seeding represents the best option. Planting a crop such as oats, sorghum or other early harvested crop may help in that some of the toxin may be removed through plant uptake. If alfalfa must be planted in spring following a spring killing of an old alfalfa stand, wait at least three weeks before reseeding. In all of the scenarios discussed above except rotating out of alfalfa for at least one year, some yield reduction will likely be experienced. In the case of a spring-kill followed by spring replant, serious yield reductions are possible.
How does autotoxicity affect plants?
Autotoxicity affects the development of the seedling root system. Toxins inhibit the ability of the root radicle to elongate. This results in reduced seedling emergence. Emerged plants are stunted and may show purpling because of their inability to take up adequate amounts of phosphorus. Surviving plants will develop a secondary root system that is shallow and more highly branched than that of an unaffected plant. This smaller root system reduces the plant’s ability to take up water and nutrients. This affect will persist throughout the life of the plant. Stands affected by autotoxicity during the seedling year will have reduced yields not only in that year but in subsequent years as well. Studies in Missouri and elsewhere have documented reduced yields up to three years after stand establishment.
Planting Alfalfa (8/1/20)
FAQ
What type of soil does alfalfa like?
What is the best planter for alfalfa?
Can you grow alfalfa in pots?
When to replant alfalfa?
When should I repot my alfalfa plant?
By the time your plant has depleted the nutrients in its soil it’s likely grown enough to need a larger pot anyway. To replenish this plant’s nutrients, repot your Alfalfa after it doubles in size or once a year —whichever comes first. Alfalfa prefers for the soil to dry out between waterings and should be watered regularly.
Should I test my alfalfa before planting?
Soil testing is recommended before planting to ensure the right conditions. If necessary, lime can be added to increase the soil pH, and organic matter can improve soil fertility. According to a study by Purdue University, alfalfa can tolerate a wide range of soil types, from sandy to clayey.
Is alfalfa good for soil?
Alfalfa is highly nutritious and a natural source of nitrogen. It’s ideal for improving the soil and providing erosion control. Alfalfa’s extensive root system nourishes both plants and soil. The alfalfa plant has been cultivated for generations and growing alfalfa in your garden is easy.
How far do alfalfa roots spread?
Note that alfalfa taproots can drill down more than 10 feet, and the roots close to the surface can spread 20 feet or more. The plants will grow most quickly in well-draining soil, but the taproots can also break up rocky soil, so feel free to pick an area with compacted earth.